Two Dimensional Engineering Drawing Using Microstation V8 CAD

Bryan Attewell 10/08/2005

Introduction These notes introduce the computer aided drawing (CAD) program Microstation, which the University currently uses for two dimensional engineering drawing. By reading through this text and working through the examples, you should become a reasonably competent CAD draughtsperson - a skill that could assist you with your design assignments and your final year individual project. Many companies, particularly smaller firms, continue to use two dimensional drawing. Knowledge of 2D CAD could therefore help in finding a work placement and an eventual full time job. Every mechanical engineer needs to know how to read an engineering drawing. The notes do not cover the basic elements of engineering drawing. An introduction is given elsewhere in the course, but it is strongly recommended that you purchase a reference book that will be useful whenever you have to make engineering drawings. It is “Manual of Engineering Drawing To British and International Standards”. 2nd Edition. C. Simmons. D. Maguire. Edward Arnold. ISBN: 0-7506-5120-2. You can obtain a personal copy of Microstation, this is not essential for on campus students, but you might prefer to have a copy on your own computer. I will be letting you know how you can get a copy during the year. Competence in engineering drawing only comes through practice. It should form a pleasant contrast to the more analytical studies that you cover elsewhere. I hope that you will enjoy working through these materials and get as much pleasure from using the CAD system as I do. Bryan Attewell 02/08/2005

Table of Contents Introduction...................................................................................................................... 0 CAD Lesson 1 - An Introduction to CAD and Microstation V8 ..................................... 3

Good and Bad CAD Drawing ...................................................................................... 5 Units and Resolution.................................................................................................... 7 Starting and Configuring Microstation ........................................................................ 8 Setting up a standard set of levels .............................................................................. 12 Dimension Size .......................................................................................................... 20

CAD Lesson 2 - Basic Drawing Using Accudraw......................................................... 25 Co-ordinates in Microstation ..................................................................................... 26 Absolute Co-ordinates................................................................................................ 26 Relative Co-ordinates................................................................................................. 27 Starting Accudraw...................................................................................................... 28 Erasing Lines.............................................................................................................. 36 Using Snaps................................................................................................................ 37 Using Levels .............................................................................................................. 40 Fillet Radii.................................................................................................................. 42

CAD Lesson 3 – More Accudraw................................................................................. 48 A Return to the SNAP................................................................................................ 48 Drawing with respect to a point Using Accudraw ..................................................... 48 Snappy Drawing......................................................................................................... 52 Locking Accudraw On to an Axis.............................................................................. 54 Locking distances or an angle using Accudraw......................................................... 55 Aligning The Accudraw Compass to Any Line......................................................... 57 Accudraw and Smartline ............................................................................................ 58

CAD Lesson 4 - More Tricks......................................................................................... 66 Drawing Lines Parallel to Existing Lines .................................................................. 66 Trimming and Extending Lines ................................................................................. 68 Extending Elements ................................................................................................... 70 Mirror ......................................................................................................................... 71 Using the view commands ......................................................................................... 73 Copying and Moving ................................................................................................. 75 A Standard Drawing Border....................................................................................... 77 Using the Axis Lock .................................................................................................. 85

CAD Lesson 5 - Projected Views and Ellipses.............................................................. 87 Circles on Sloping Surfaces ....................................................................................... 88 Auxiliary Projection................................................................................................... 88 Drawing arcs and circles to touch particular points on the drawing .......................... 88

CAD Lesson 6 - Arrays, dimensions and tolerances ..................................................... 91 Using the Construct Array command......................................................................... 91 The Rectangular Array............................................................................................... 93 Dimensioning Drawings ............................................................................................ 95 Dimensioning Diameters, the letter ∅ ....................................................................... 98 Applying Tolerances To Dimensions ...................................................................... 104 Limits and Fits ......................................................................................................... 106

CAD Lesson 7 - Cells, Hatching, and Printing ............................................................ 114 Using Cells In Microstation ..................................................................................... 114 Sections and Hatching.............................................................................................. 121 Printing and Plotting ................................................................................................ 125

1

Past Paper ..................................................................................................................... 129 Marking Scheme ...................................................................................................... 131

2

CAD Lesson 1 - An Introduction to CAD and Microstation V8 Introduction This series of lessons introduces the recommended computer aided drawing (CAD) program Microstation. Microstation is a very large and powerful piece of software with thousands of commands and features. It is capable of sophisticated three dimensional modelling, having the ability to produce photo realistic rendered views. We will be merely scratching the surface of this complex program within this unit, and will be concentrating on two dimensional engineering drawing as it applies to mechanical engineering. If you wish to further explore Microstation, the program does have a substantial in-built help system to allow you to have a go independently. You may be more familiar with Auto CAD, which we did use some years ago. The decision was taken to transfer to Microstation as that software was available to students for home use at a lower price than AutoCAD. Microstation provides all of the facilities of AutoCAD, and is in some ways easier to use. It is to your advantage to be familiar with more than one CAD package, so if you have already learned to use Auto CAD, Microstation will be a bonus! Microstation has an international user base; one of its most famous clients is the design firm led by Norman Foster. Some of its more famous applications in the UK include the Jubilee line extension in London and, closer to home, the futuristic new Sage concert hall in Gateshead. In this particular lesson I intend to talk about CAD in general, and then will go on to discuss how to configure Microstation to best meet our requirements. The aim of the lesson is to set up a standard drawing format that can be used in all subsequent work. We will not be doing any actual drawing in this first lesson, be patient, it is necessary to lay a solid foundation before moving on. Aims At the end of this lesson you should be able to :- • understand the advantages of CAD over manual draughting • know what constitutes good practice in CAD • understand how Microstation uses units (e.g. mm, feet etc.) and set up a standard

drawing using appropriate units. • understand how Microstation uses layers and set up a standard drawing using

appropriate layers. Study Advice This series of lessons assumes no previous knowledge of CAD. They do assume that you are reasonably familiar with Windows based software, e.g. that you can confidently

3

open, close and re-size windows and are familiar with pull down menus and the use of a mouse or other pointing device. Microstation can usefully employ a three button mouse or tracker ball, but a two button device can also be used satisfactorily. The two buttons are depressed simultaneously to provide the “third” option. Bentley Microsystems does maintain a useful World Wide Web page which includes the answers to many frequently asked questions about Microstation. If you have access to the internet you should visit http://www.bentley.com, while there are also Microstation newsgroups. Drawing using a computer CAD enables even the novice draughtsperson to produce work of a professional standard. In the days of manual draughting it was customary for beginners to have to spend hours merely learning how to print neatly - while the proper manipulation of the drawing instruments required further hard won skills. It still remains necessary to understand the conventions of BS308 and orthogonal projection however; the CAD user must be able to visualise a 3D object in two dimensions. In some ways CAD makes this process more difficult, as when the full drawing is shown on the screen, the details may be too small to distinguish. Only when the CAD user zooms in on a small section of the drawing is it possible to read the small print, or see the precise way in which the entities have been put together. While never a super skilled draughtsman, I enjoyed working on the drawing board, but I can honestly say that I get more fun out of using a CAD system. There are no real limitations on space, you can amplify the drawing by huge factors, copy bits, move chunks around, and work to an accuracy that would be impossible with manual draughting. Time evaporates when you are putting together an engineering drawing. I hope that you will share my enthusiasm for this work, and get as much pleasure from it as I do. CAD has, to some extent, reduced the need to carry out trigonometric calculations and use basic geometry, but there remain occasions when the CAD user must be able to do this. ITQ When used in a commercial environment CAD has many advantages over manual draughting, can you name some of them?

4

Some of the advantages of CAD include:- • greater accuracy. • clever tools to draw common features e.g. chamfers, fillets etc. save time. • rapid copying of drawings or sections of drawings greatly increases productivity. • libraries of standard parts are available for immediate insertion into drawings. • possibility of sharing the latest designs using a network, essential for concurrent

engineering. • semi automatic dimensioning reduces errors and increases productivity. • interfaces with other company systems, e.g. MRP, CNC machines, rapid

prototyping, finite element analysis etc. Good and Bad CAD Drawing Just as when doing manual drawing, there are good and bad practices with CAD. The lazy CAD user will guess the location of lines, while the dedicated professional will zoom in until it is absolutely clear where the lines are being placed, and then use the automatic detection aids within the program to positively snap onto the required location. This is a theme to which I will be returning - experience of teaching CAD has shown that it is not possible to over-emphasise the importance of care and precision in computer drawing. All CAD programs provide drawing grids to assist the user. Lines can be made to automatically SNAP onto the points on the grid. Novice users tend to use the grid extensively. It is normally preferable, however, to switch the grid off when beginning to draw as otherwise lines will mysteriously snap onto positions that are not required. Similarly, modern CAD programs provide slick windows based drawing aids which encourage inaccurate free hand sketching - this is the road to ruin, be warned !!! The ONLY way to reliably and consistently produce good quality CAD work is to use typed dimensions entered via the keyboard, especially when a new drawing is being created. In the later stages of drawing, when many of the principal lines are in place, it is possible to make good use of the clever drawing aids that do not require co-ordinate data. Now most CAD programs require that you understand the difference between absolute and relative co-ordinate positions. You specify a particular place on your drawing sheet using absolute co-ordinates, and then move relative to that position. For example you specify a point that is 200 mm in from the left hand edge and 100 mm up from the bottom. You can then specify another point, relative to the first, that is 50 mm to the right, and 30 mm higher than that first point. Microstation has a unique data entry system called Accudraw that removes the need for much of this ponderous procedure. While Microstation does support both absolute and relative co-ordinates, and has an appropriate data entry mode, we will only briefly encounter it in this course, and will rely to a large extent on Accudraw. You may or may not have used a drawing board, but you will almost certainly have had to draw a graph. One thing that these two activities have in common is the need to choose and use a scale. Thus manually produced drawings would be made that were

5

perhaps 1/10 th. full size, or maybe 2 x full size, depending upon the circumstances. In CAD it is easier and altogether much preferable to draw to size. If it is 5 m long, draw it 5 m long!

*** Remember, do not scale your drawing - draw everything to size ***

Even if you remember nothing else from this first lesson, please take heed of this advice. You can worry about the eventual drawing size when the time comes to print or plot it out. Normally it is possible to drop a drawing border of the appropriate size onto your masterpiece at the last minute, and, if necessary, scale the drawing border to fit. The CAD program will make everything fit, and you can plot it out to a standard drawing size. Your drawing will have the correct proportions, but may be of an indeterminate scale. If you are trained in manual draughting this no doubt sounds like a heresy, but don’t worry about it. Remember all engineering drawings should carry the legend “Do Not Scale”. Manufacturers should make parts to the stated dimensions, not measure off the drawing. It is also possible to plot a drawing to a precise scale, if required. This may be needed, for example, in the production of a master for an electrical circuit board.

6

Units and Resolution Microstation can handle many different types of units, e.g. feet and inches, metres and millimetres, etc. It is possible to change the settings of the program to accommodate the units that you want to work with. For our purposes the most useful unit is probably the millimetre, but if we were doing civil engineering it might have been the metre or the kilometre. This practical unit is described as the MASTER UNIT. Microstation then allows us to define a SUB UNIT, which is a fraction of the master unit. In civil engineering we might have adopted a master unit of a kilometre with a sub unit of the metre. In our case we might adopt the following:- Master Unit Millimetre Sub Unit Micrometer Having chosen our master and sub units, there is one final choice open to us, that is the resolution that we wish to work with. Now there needs to be some compromise here, as a finer resolution will result in a smaller overall drawing area, but the sizes involved are such that they do not present any realistic obstacles to doing our work. In Microstation V8, the degree of resolution varies over the drawing area, and the resolution that we are able to set is actually the minimum value that exists at the very edges of the virtual drawing plane. That drawing plane can be measured in kilometres, while our drawings, situated within the central area of the plane, will be in measured in millimetres or metres. The actual useful resolution is very much higher than the minimum. Using Levels in Microstation All serious CAD programmes provide the ability to split a drawing into several layers or levels. Levels can be thought of as being analogous to a series of sheets of tracing paper which can be viewed separately or overlaid. Different elements of the drawing can be placed on different levels, e.g. construction lines can be placed on one level, dimensions on another etc. It is very useful to be able to “switch off” the construction lines while drawing, and concentrate on the main view. Levels allow us to bring into play, or remove, different sets of elements at will. You are free to decide how best to use levels within your drawing. In complex projects it would be advisable to use different levels for different kinds of components, e.g. pipe systems, supports, main machinery etc. In the introductory work that we will be doing levels will be associated with different types of lines, rather than different types of components. So we will establish a level for each of the following types of lines:- • main drawing outline • construction lines

7

• hidden lines • centre lines • dimensions It is useful to use different colours for different line types, while hidden and centre lines have particular styles of lines. Further, BS308 requires that we use different line widths, or weights, when producing engineering drawings. Again we will set up a template to define suitable values here. Starting and Configuring Microstation Having considered some of the issues the time has come to switch on the computer and get into Microstation. In this session I hope to show you how to create a standard drawing file that can be used for all future work. It will have the following features:- • suitable units • named levels with various line-types and colours • the grid suitably configured, but switched off • a standard size for text Get into Microstation, by double clicking the V8 Icon on your desktop. A window should appear on the screen entitled “Microstation Manager”. Chose File and then New. A second window appears entitled New, fig 1. Type des1in the empty space provided.

***Do NOT press the Enter key at this stage***

8

Figure 1. The next task is to select a SEED file that will specify the units required. Click onto the Select button in the SEED file window, and then pick the seed2d.dgn file. Choose OK.

Figure 2 This will return you to the New window. Pick OK again, when you will be returned to the original Microstation Manager window. Pick OK a third time when you will finally start up the program.

9

Note that you will normally have to click onto OK, or possibly Apply, in order show Microstation that you have finished making your choices and want to move on. In future I will expect that you will do this automatically. There will be a delay and then the main Microstation drawing screen will appear. If you have bought the academic version of the program that screen may be overwritten by a Restricted Use message. That message box should be dragged off the screen using the mouse. First we will check that the correct units have been selected. Choose Settings followed by Design file. Click on Working units, when the details of the units should be displayed, fig. 3. Change the master units to Millimeters and the Sub units should be automatically changed to Micrometers Remember. Note the USA spelling of meter, rather than metre!

Figure 3 Now select Advanced and, ignoring the warning message, change the resolution to

10

10000 per Centimeter. Click OK to move back to the DGN file settings window. While we have this design file open, it is useful to deal with the grid. While I rarely use the grid, we might as well have a grid that will be useful, and now is a good time to make it so. Click onto Grid. Now adjust the Grid Master to be 1, i.e. a grid spacing of 1 mm, and make the Grid Reference =10. ( Every 10th grid point will be shown highlighted). Finally, if necessary, switch off the grid lock by clicking in the little box containing a symbol annotated Grid Lock. The symbol within the box should disappear, indicating that the lock is off. Click on OK (fig. 4).

Figure 4

11

While we are at it we might as well switch the grid display off. Choose Settings, View attributes when the View Attributes window will appear, fig. 5. Click in the little box adjacent to the word Grid, when the x will go. Finally Apply these settings and close the window by clicking on the X in the top right hand corner. It is occasionally more convenient to have the grid on, in those cases you can quickly undo the previous steps.

Figure 5 Setting up a standard set of levels Next we will set up following levels. • main drawing outline (Default) • construction lines • hidden lines • centre lines • dimensions I suggest that you adopt the following convention regarding line colours and styles:- Level Name Colour Style Width 1 Default White (0) Solid (0) Heavy (1) 2 Construction Blue (1) Solid (0) Light (0) 3 Hidden White (0) Dashed (2) Light (0) 4 Centre Green (2) Chain-dotted (4) Light (0) 5 Dimensions Magenta (5) Solid (0) Light (0) Microstation allows you the freedom to choose any colour or linetype on any layer and to mix different linetypes and colours on any layer, or, if you prefer, to restrict the

12

choice to a given line specification on any one layer. I feel that it is preferable to use layers to effectively select the linetype, so I recommend that you restrict each layer to a given linetype. Once you have decided upon a convention, you can save it and use it with all of your drawings. This makes for an efficient use of your time, e.g. you quickly get used to selecting level 2 for construction lines, and you know that all construction lines will be in blue, and not quite as wide as the main drawing lines. How do you set up a standard for layers in your drawings? To set up the drawing levels in the way we require it is necessary to make some changes to the Design File. Select the Settings drop down menu, and then pick Design File.

When the Design File (DGN File) Settings window appears, pick Element Attributes and set the selections as shown in the illustration below. What we are doing here is to tell Microstation that we are going to select colour, line style, and weight by choosing the appropriate level (ByLevel).

13

Having instructed Microstation to select line attributes by level, and confirmed this, by clicking OK in the DGN File Settings window, we now can move on to specify the particular colours and styles that we require. In order to do this we need to open the Level Manager window. Select Settings, Level, Manager as shown below, when the

Level Manager window will appear as shown below

14

Choose Levels, New, when a New Level will be created.

You can now modify this new level to have the attributes that are required. For example we will set up this new level to represent centre lines. The centre lines will be green in colour and will use a chain dotted line type. Finally we will change the name of the level from New Level [0] to Centre. Left click onto the little square on the New Level line in the Color column. The Level Color window will appear. Pick the green colour which is in the top left hand corner of the matrix, the third little square along from the left.

15

Now move over to the Style column and left click the small section of line shown there. When the Level Style window opens, select the chain dotted line type 4.

Finally right click the name, New Layer and choose Rename. Type in the new name which is Centre.

16

Create further new layers to represent Construction, Hidden and Dimension lines as shown below. Finally change the weight of the Default line style from 0 to 1. You should end up with the Level Manager looking like that shown below.

To select a level as the active level, right click on the required level, and then left click on the Set Active command.

17

Having selected the Centre line type, the next and all subsequent lines will be drawn as centre lines, green in colour and with a chain dotted style. Now let’s try to draw some of the lines. Pick the symbol from the left side of the screen that looks like an electric light bulb.

Hold down the mouse key on the symbol when the contents of the Linear Elements drawing toolbox will be displayed.

Pick the simple sloping line symbol second in from the left on the top row. This then becomes the selected drawing tool.

18

Go anywhere on the drawing screen and use the left mouse button to start and end a line. Use the right hand mouse button to stop drawing that line. Choose each of your line types in turn and draw a single line on the screen to illustrate the use of the different levels as shown below: -

Now there are easier ways to select the required levels than using the Level Manager. Close the Level Manager and use instead the level selection window located at the top of the screen. One left click will select the required level.

Alternatively, and more powerfully, you can use the command Control E (Control and E keys pressed simultaneously) to call up the Level Display window. Now you can pick the required level from the list. A single key press on a level name will toggle between the level being on or off. If the level is off, then the lines drawn in that level are also off, while if it is on, the lines are shown on the screen. If you double left click on any one of the levels, it will become the selected drawing level. The diagram below shows the Level Display window, with Construction as the selected drawing level. Default and Dimensions are switched off, while Centre and Hidden are switched on.

19

Having set up your different levels you can see that the Level Display window allows you to manipulate them quite easily. When you turn a layer off, it does not mean that it has gone for good; merely that it is not displayed on the screen. It can be turned back on again at any time. Make sure that you do not leave until you have turned all of your layers back on, and have selected level 1 as the currently active level. This is the default setting that we will normally be using when starting to draw.

Text Size

We can set a convenient text size by choosing Element, Text Styles, when the Text Styles window appears. I suggest that you select a text Height of 4 mm and a text Width of 3 mm. You will need to click in the Value column to be able to make the required changes.

Dimension Size

Similarly we can set the size of dimension text, which will automatically change the proportions of the dimension settings to suite.

Choose Elements, Dimension

20

and then Text. Click in the Height and Width boxes and apply the values 4 and 3.

Close the Dimension Settings window.

Further Configuring

The figure below shows the screen display that we will achieve after this section of the work. Your screen may already appear like this, depending upon how your software was installed, but in any event I will show you how to set it up.

Pick the Tools drop down window and ensure that Attributes, Primary and Standard are all selected.

21

A couple of final points and we are finished. Many users will prefer to have the small drawing cursor replaced by a pair of cross hairs that cover the entire screen. This is achieved by choosing Workspace , Preferences when the Preferences window (fig. 16) opens. Choose Input, Pointer Size, Full View.

We have finished for now, choose File, Save Settings, Exit.

22

It is important to note that Microstation normally saves every change that you make to a drawing automatically, but it does not automatically save changes to the set up, i.e. levels etc. You must specifically choose to save the settings if you wish keep them for future use.

Bryan Attewell

28/07/2005

Self Assessment Questions

1) By what practical measures do you ensure that your drawings are made accurately, and how do you select a suitable scale when beginning to draw?

2) What are, and what is the purpose of, levels in CAD?

23

Answers to Self Assessment Questions

1) Good practice involves the use of typed co-ordinates to specify sizes and distances. The successful CAD draughtsperson will always zoom sufficiently into a drawing to ensure that it is clear where all features are being placed. Free hand drawing or guessing is the road to ruin!!

It is generally better not to scale when drawing with CAD, all parts should normally be drawn to size.

2) Levels may be thought as being analogous to overlain sheets of tracing paper, each one carrying particular information. Individual levels can be switched on or off, while only one level is normally active at any one time, i.e. it is the level on which drawing is currently taking place.

It is up to the user to decide how to organise levels, and in complex applications they may be used to represent different features of the machinery or plant under consideration, e.g. oil lines, coolant lines etc. In our work we will be using a different philosophy, the layers will hold different linestyles and types, e.g. main drawing, construction, dimensions etc.

Summary Having completed this lesson you should:- • understand the advantages of CAD over manual draughting • know what constitutes good practice in CAD • understand how Microstation uses units and set up a standard drawing file using

appropriate units. • understand how Microstation uses layers and set up a standard drawing file using

appropriate layers.

In addition you should possess a design file called DES1.DGN that can be used as a standard configuration for your future work. In future sessions you can start by loading DES1.DGN, and then immediately save it as a different name - that way you will not inadvertently change it. I will return to this in the next lesson.

As you gain confidence with Microstation you will no doubt develop personal preferences in the use of the software that may be different from mine, there is nothing to stop you from modifying your design file accordingly.

24

CAD Lesson 2 - Basic Drawing Using Accudraw Introduction In the previous lesson you constructed a basic design file called des1.dgn. That file selected the mode of operation that you will subsequently be using for all drawings in terms of units, line types and grid settings. In this lesson we will be loading in that design file, saving it as a different file, and then doing some basic drawing using typed co-ordinates. Basic drawing includes the use of absolute and relative screen co-ordinates, straight lines, circles, and arcs. We will also find out how to snap onto particular points of a drawing and how to erase sections of a drawing. Accudraw is a context sensitive drawing aid. It tries to determine what you intend to do next by tracking the movement of the mouse pointer, and then presents the most convenient way of achieving your intention. More than that, it remembers past settings, and will optionally recall distances and angles for your use. One major advantage is the way in which it can be used to define a new origin with respect to any key point on your drawing. This greatly reduces the need for construction lines and generally speeds up the job. Another useful feature is Accudraw’s ability to optionally provide orthogonal lines. Accudraw significantly assists in 2D drawing, and it is an invaluable aid in 3D. A single key press results in the Accudraw cursor aligning itself with the required 3D plane Take it from me, Accudraw is the “bees knees”. A complete book has been written on Accudraw [1], we don’t have time to spend exploring its every asset on this course, and instead we will be concentrating on the sub set of key attributes that are the most useful in daily use. Aims At the end of this lesson you should be able to:- • understand relative and absolute co-ordinates • use Accudraw to construct simple drawings • draw lines, circles and arcs • erase sections of the drawing • understand and use snaps • use the circular fillet command • use levels for different linetypes Study Advice You should have completed the first CAD lesson before starting this one.

25

CAD can be addictive, don't spend too long in front of the monitor at any one time - a one hour session is quite enough to begin with. Co-ordinates in Microstation If we confine our work to two dimensions we can imagine a flat rectangle of “paper” stretching several kilometres in each direction. Microstation works with the normal convention in that movement to the right (the x direction) is positive while that up the paper (in the y direction) is also positive. Conversely movement left or down is considered negative.

Microstation allows two possible ways to handle co-ordinates, absolute or relative. Absolute Co-ordinates Absolute co-ordinates work in the same way as when you draw a graph. All points are defined with respect to the origin, e.g. it is possible to select a point that is 100 units to the right of the origin and say 50 above. The command is

xy=100,50 A line can be drawn by specifying the start point followed by the end point, e.g. a horizontal line that is 50 mm long and whose start position is 100 mm above and to the right of the origin will be drawn from 100,100 to 150,100. i.e. from xy=100,100 to xy=150,100. Note that the expression above is not a valid Microstation command, don’t try to use it. ITQ If you wanted to draw a vertical line of length 100 mm from a point 50 mm above and 50 to the right of the origin, what would the absolute co-ordinates of the start and end points be? Answer From xy=50,50 to xy=50,150

26

Relative Co-ordinates Absolute co-ordinates require that all positions be specified with respect to the origin. This is possible but normally rather inconvenient. It is much easier to specify lines with respect not to the origin, but rather to some other point on the drawing, i.e. it is easier to specify a line 50 mm long than have to work out the co-ordinates of the end point with respect to the origin. In practice it is rarely worth worrying about where the origin is in CAD. The drawing plane is so large that I have never found myself beginning to fall off the edge, wherever I start to draw. This is another major difference to manual draughting, in CAD you start to draw wherever you fancy, the virtual drawing sheet effectively removes any real restrictions on size or placement. Relative co-ordinates are so useful that Microstation provides two sets, rectangular co-ordinates and polar co-ordinates. In both cases the effective origin is the current cursor position on the drawing. Entities are drawn with respect to the last point that has been defined. The rectangular relative co-ordinate instruction takes the form:-

dl=x_displacement,y_displacement

e.g. dl=30,0 This instruction implies a move of 30 mm to the right of the current cursor position. The d in dl stands for ∆ delta, the symbol normally used to represent a small displacement. The polar relative co-ordinate instruction takes the form:-

di=line_length,angle

e.g. di=50,45

This would move to a point at a radius of 50 mm from the current cursor position and at an angle to the horizontal of 45 deg. The sign convention adopted for angles is positive anti-clockwise. ITQ a) How would you specify a line that ended 100 mm higher and 80 mm to the left of the current position? b) How would you specify a line of length 200 mm at 45 deg clockwise from horizontal?

27

Answer a) dl=-80,100 b) di=200,-45 If you have used another CAD program in the past, e.g. Auto CAD you will perhaps be familiar with these concepts. In fact Microstation has a much better way of drawing than having to work out coordinates. It is called Accudraw, and, believe me, it is the best in the business! You can draw in Microstation using absolute and relative coordinates using keyed in data, but we won’t waste time with further references to this, but rather we will move straight on to enjoy the benefits of Accudraw. Starting Accudraw Load your standard design file des1. You should see a symbol comprising a square containing a small circle. That is the Accudraw toggle button.

If you can’t see the symbol on your drawing screen do the following:- 1. Tools 2. Click in the box adjacent to Primary Tools

If Accudraw is already up and running you should either see two data entry boxes near to the bottom of the screen as shown below, or the Accudraw window on the screen. The Toggle Accudraw button switches Accudraw on and off.

If you can’t see either of the Accudraw data entry windows as above, click on the Accudraw Toggle button. You should then see the message Start Accudraw point input tool at the bottom of your screen, while the Accudraw window should open on your screen as shown above. It won’t necessarily contain the same numbers as those shown.

28

It is convenient when using Accudraw to drag the window down to the bottom of the screen where it will lodge itself out of the way as shown below. Again do not be concerned if the numbers in the boxes are not the same in your example.

I suggest that you File, Save Settings at this point, to preserve this set-up of Accudraw to your des1.dgn file. Now use Save As to save the file again as Accu1 to carry out the exercises that follow. The original DES1.DGN file should be kept as an empty drawing file that can be used to start all of your subsequent work. You should therefore not begin to overwrite it with extra commands. When starting a new drawing, always load DES1.DGN first and then save the file with a different name, before starting to draw. Our first task is an easy one, we are going to draw the object shown in fig. 1 below, without the dimensions.

Figure 1 If you have configured DES1.DGN correctly your drawing should be set up to begin drawing on the main level, the Default level. The level indicator is shown near to the top left hand corner of the screen, below the Edit button.

29

If it shows a layer other than the Default, then click onto the indicator and change it to Default. In order to draw we have to first select the line drawing too. The various toolboxes are located to the left of the screen.

Behind each element in the tool box resides a further set of tools. Holding the left mouse button down on the chosen element will cause the extra tools to slide out. Release the mouse button and they will slide back in again. Try this now, look at all of the available tools, you will find that all but two of the buttons have pull outs. You can select any of the tools on the slide out bar by moving the cursor over to that tool and then releasing the button. That tool then becomes the operative one, and is the tool that is displayed in the main tool box. We want to pick the line drawing symbol, which is a straight line, drawn at an angle. It appears, along with other line drawing tools (linear elements), on the slide out bar behind the symbol that looks like an electric light bulb - in the second row and second column of the tool box. Alight on that using the mouse, hold down the left button and then move the cursor onto the single line symbol shown in below. Finally release the button. The line drawing symbol should now become the default value in the tool box.

N.B. Do NOT use the line drawing symbol with the electric light bulb symbol for drawing, always select the simple sloping line shown above. It is possible to extract the slide out window and display it on your drawing screen as shown below. This is achieved by dragging the window either up or down. I have extracted the line drawing (Linear Elements) window in this way. It can be replaced by clicking in the top right corner in the normal Windows fashion. It is sometimes useful

30

to have a full set of tools available like this while drawing, but most of the time they get in the way.

You should now see a small box appear on the screen marked Place Line

If the box is positioned in an inconvenient spot, drag it out of the way, the top right hand corner of the screen is a satisfactory location. Check to see that the two little boxes to the left of the words Length and Angle are both empty. If either or both of them are not click onto the little boxes to empty them as shown below. You should also see some numbers to the right of the words Length and Angle, but you can ignore them.

figure 4

Before taking the plunge, let’s consider how to retrieve things if you make a mistake. There are at least two ways of correcting errors. The simplest is to use the Undo button at the top of the screen.

Alternatively you can delete any one drawing element (e.g. line) by picking the delete button and selecting the line to be deleted.

Now we can start to draw. We are going to draw the simple component shown below. Start at the bottom left corner and work round in an anticlockwise direction by choosing to draw the horizontal 200 line first.

31

With the place line tool selected and Accudraw activated click the left mouse button (LMB) near to the bottom left corner of the screen. The Accudraw compass should appear as shown below.

Move the cursor so that the line is more horizontal than vertical and press the Enter Key when Accudraw will lock to the horizontal.

Microstation is now expecting you to enter the horizontal length of the line (it knows that you will not be wishing to enter the vertical height as you have constrained the line to be horizontal.)

Note how the cursor is flashing in the X box, while the Y value is locked at 0.0000. Your X value will probably be different to mine.

32

Without having to select the X box just type 200, the length of the line, Microstation works out what you want to do and places that value in the correct place and locks the line to that value.

Press the left mouse button (LMB) to accept the line. Depending upon the scale at which your screen display has been set, you may or may not be able to see the end of the line. In my case the end of the line was off the screen and I could only see part of the horizontal line and another line starting from the end of the line whose length and position is controlled by my mouse cursor.

Accudraw is therefore ready to continue drawing from the end of the previous line, but we cannot see it at present. Let’s put that right. Move the cursor over the screen view controls and select the one that looks like a mountain range, selecting with the LMB, to fit your drawing to the view using Fit View.

Now press the right hand mouse button (RMB) when Accudraw will resume drawing where you left off.

33

Move the cursor vaguely vertical and press Enter when Accudraw will lock to the vertical and Microstation will expect you to type the vertical length of the line; which is 100.

Press the LMB to accept this and then fit to the view again (Mountain symbol). Press the RMB to resume and move off to the left to draw the remainder of the figure.

Draw a horizontal line 50 long, followed by a vertical line 40 long and another horizontal line 100 long. Note the sequence. Move vaguely horizontal or vertical to taste, and press Enter to lock. Type in the required value and confirm using the LMB. When you are finished drawing the RMB exits the drawing command, so don’t do this until you have finished!

Once you have got so far through the drawing you can start to pick up on points on the geometry that have already been defined.

34

At this stage you want to draw another vertical line that is 40 long, and you can pick up that length from the existing geometry to the right. Lock to the vertical using the enter key and then select (LMB) the left end of the short horizontal line that you have already drawn as shown above.

Use the same trick again to fix the length of the 50 long horizontal line by picking the bottom left corner of the view. Finish off by picking the bottom left hand again using the LMB, and then the RMB to exit the line drawing command.

35

Erasing Lines We are going to erase the drawing that you have just created, before drawing it again for practice. There are a number of ways to erase lines. I will show you two methods. First click onto the erase symbol button. Now click onto any one of the lines using the left button, the line should become highlighted in red. At this stage you can either click the left button again to accept that the line should be deleted, or press the right button to reset the command without deleting the line. In this case we will delete the line by clicking the left button.

That method is fine if you want to erase only one or two lines, but a bit tedious if you have a lot of erasing to do. There is a faster way. First we will shrink our drawing a bit. Click onto the Zoom Out button and click at the centre of the screen.

36

What I intend to do is to erect a fence around all of the elements to be erased and then to erase the contents of the fence. Click onto the draw fence button and then position the cursor above and to the left of the top left hand corner of your drawing, click the left button. Now drag the cursor down to below and to the right of the bottom right hand corner of your drawing. Click again. You should now have drawn a fence around the drawing.

Fence Button Now go back to the fence symbol and hold it down until the remainder of the related command buttons slide out. Click on the erase fence button. Now click anywhere on the screen and the contents should disappear. Finally slide out the fence button when a single click on it will remove the fence.

Erase Fence Contents The concept of the fence is used extensively in CAD, you will encounter it again when we learn how to move or copy sections of drawings. Having erased the drawing; try to draw it again. Continue to draw and erase until you can do so without reference to the notes. Using Snaps What is a snap? It is a position to which the cursor will snap to, for example the end of an existing line. It is impossible to over emphasise the importance of using snaps in CAD. They ensure that your drawing is produced accurately, all of the points being where you intend them to be. Resist at all costs the temptation to guess at the starting point for a line or other drawing element.

37

The default snap is keypoint, which is the third symbol in from the left in the figure above. Keypoint will cause Microstation to snap onto the end or midpoint of a line or arc. It will also snap to the centre and four quadrants of a circle. Because Keypoint is the default there is no need to specifically select it, it is normally ready for use. ( If you want to see the range of snaps as in you should click on the Keypoint button which resides near to the bottom centre of the screen, when a menu of the snaps will appear. Then choose Button Bar to obtain the contents.).

Now we will draw a more complex shape, involving a circle, an arc, and radii. The finished drawing is shown below, but we will not be including dimensions in this exercise.

38

First erase your previous drawing. Remember a convenient way to do this is to draw a fence around it and then use the delete fence contents command. We will start by drawing a rectangle 150 long by 100 high. Next we will draw the arc at the right hand end. A construction line will be used to determine the position of the centre of the circle, while Microstation’s automatic fillet radius command will be used to draw the two radii. We will complete the drawing by including the three centre lines.

To draw the arc, choose the arc button shown below.

You will be asked to identify the first arc endpoint. Place the cursor near to the top right hand corner of the rectangle. A cross should appear on the intersection at the corner. Accept this by pressing the left hand mouse button.

You are now asked to identify the centre of the arc. Move to the approximate middle point of the right vertical line and snap to the mid point of the line which is the arc centre.

39

Finally do the same at the arc end point, at the bottom of the vertical line. Your drawing should now look like that shown below

Accept the point with the LMB and leave the Arc command with the RMB.

Using Levels We will now draw a construction line to help determine the position of the circle. If you recall we arranged in the last lesson to use level two for our construction lines. To make use of that facility we must change the active level. At the top left of the screen will be found a small inverted triangle with the name of the current level alongside it. This should indicate that we are currently using the Default level. If we click the mouse onto

40

the triangle and hold the button down we will see a table of the levels appear. The mouse can then be used to select the required level. We want the construction level.

The circle centre is located on the mid point of a line joining the mid points of the two horizontal sides of the drawing. Select the line drawing button and then snap to the bottom mid point, finish the line by snapping to the top mid point. If you used the colours that I advocated in the first lesson this line should be shown in blue.

Now to draw the circle. It will be necessary to first switch back to the default level, as the circle is not a construction line.

Pick the circle drawing tool as shown above. Set the diameter to 60 (or the radius to 30, don’t confuse the two!)

41

It will request that the centre be specified, snap onto the mid point of the construction line to achieve this.

Now erase the right hand vertical line.

If all has gone according to plan your drawing should look like that shown above. Fillet Radii Now for the radii at the two remaining corners. Microstation provides a useful automatic fillet radius tool that makes light work of this. We first have to tell the program what fillet radius we want and then indicate which parts are to be filleted!

42

Select the fillet tool from the Modify section of the main toolbox which is located at the bottom right hand of the toolbox. A further small window should appear entitled “Construct Circular Fillet”. Click into the Radius box and change the value to 20.0000. Next click onto the Truncate box and select Both. To place a fillet radius required two clicks of the left mouse button. You have to select each line in turn when the fillet will be drawn. Click onto the bottom horizontal line, followed by the left hand vertical straight line. Repeat the exercise to obtain the top left fillet. You should now have a drawing that looks like that shown below.

Our next tasks are to switch off the construction line and to draw the centre lines. It is possible to switch the construction line off and switch to the centre line level using the following:- Select the Settings pull down menu, followed by Level, and then Display. Note that this frequently used set of commands can be replaced by the more convenient CTRL E key press (pressing the control and E keys simultaneously).

43

Switch the Construction level off (one click) and make Centre the current level (two clicks). Close the level control window. In order to draw neat centre lines it is a good idea to ensure that they overlap the drawing by a fixed amount on all sides. I have chosen an overlap of 15 mm. It is convenient to draw the centre lines starting from the circle centre (to which the cursor should snap), therefore that to the left will be 75+15= 90 long, to the right 75+50+15=140, and the vertical lines will be 50+15=65 above and below the circle centre.

44

The last centre line to be drawn is the vertical line through the centre of the arc. It will be necessary to locate the arc centre for this purpose, and I will use another snap to do that. First select the Draw Line command and then pick the snap icon at the base of the screen and choose the Centre snap.

Touch the cursor on to any point on the arc, when cursor will snap to the arc centre. LMB to accept and then draw the centreline upwards from the arc centre point. Don’t forget to press the Enter key to lock to the vertical, while the length of the centre line can be picked off the circle centre line as shown below.

Draw the other half of the centre line to finish the job.

45

ITQ You should know the drill by now, erase this drawing and do it again!! Don’t read the instructions unless you get stuck. The Bad News and the Good News The bad news is that there is no short route to competence in CAD - it comes from practice. The good news is that it is quite an enjoyable pursuit, particularly with Bartok or the Beatles on the “phones” and a nice cup of coffee on your desk (but not on the desks in the University computer rooms please!). SAQ 1 Draw the bracket shown in fig. 19. Include centre lines but don’t try to add dimensions.

Figure 19

Hints:- • Use snaps

46

• Draw a vertical construction line from the mid point of the base to the circle centre. • Draw a construction circle of diameter 40 using the end of the vertical construction

line as a centre. SAQ 2 Draw the shape shown in fig. 20. Show the centre lines but not the dimensions. Don’t try to draw the cross indicating the intersection of the top horizontal and right sloping lines.

Figure 20. Summary Having completed this lesson you should be able to:- • understand and use accudraw • draw lines, circles and arcs • erase sections of the drawing • use a snap to accurately locate features of your drawing • use the circular fillet command • use levels for different linetypes Bryan Attewell 02/08/2005

47

CAD Lesson 3 – More Accudraw Introduction The previous lesson introduced basic drawing commands using Accudraw. This lesson extends the use of Accudraw by considering more advanced use of snaps, resetting the drawing origin, and aligning the Accudraw compass to existing lines. A Return to the SNAP In the 2D lessons we learned that the snaps (Keypoint, Midpoint, Intersection etc.) are essential tools for accurate drawing. Microstation defaults to a particular snap mode, normally Keypoint snap. You can change the snap mode for the next operation by bringing up the snap menu and clicking on the required snap. When that operation is completed, Microstation will revert back to the default. It is sometimes useful to be able to change the default and Microstation allows this as well. One method is to change the design file setting. The sequence is as follows:- Open the Settings pull down menu and select Design File.... Now choose Snaps. Choose the snap mode that you want as the new default, e.g. Midpoint, and then select OK. Don’t forget to set it back to Keypoint. Now let’s consider using snaps with Accudraw. Using Accudraw, a single key press will change the snap mode. When the focus is with Accudraw, the snap mode can be changed for the next operation only by typing a single letter at the keyboard. The Centre, Intersection and Nearest snaps can be selected in this way by choosing the C, I, or N keys respectively. In addition, if the default Keypoint snap is chosen, Microstation responds by opening the Keypoint Snap Divisor window - which allows different settings of the divisor to be adopted. We will explore the use of snaps using Accudraw in some of the examples that follow. Drawing with respect to a point Using Accudraw We will begin using Accudraw to draw the cottage depicted below, but, before we start, I suggest that you draw a rectangle about 250 wide by about 200 high, and then fit the view (the button that looks like a mountain range) before deleting your rectangle. This will ensure that you are not running out of screen while learning to use Accudraw.

48

Figure 4

Start by drawing the rectangular outline of the house 150 x 80. The windows are a slightly more difficult proposition. Accudraw allows us to set up a new drawing origin with respect to any other point on the drawing and to start to draw from there. We will snap to the bottom left hand corner of the cottage, and then define a new origin at the bottom left corner of the left hand window. In order to do this you need to use the “Tentative Snap” command. Tentative snap allows you to snap to a point without committing to drawing anything there. When Microstation is shipped the tentative snap is obtained by pressing the left and right hand mouse buttons simultaneously. The computers at the University have been set up differently. As they use a three button mouse, or tracker ball, the tentative snap has been set to the middle mouse button. If you are working at home and have a three button mouse I suggest that you set the tentative snap to the middle mouse button. Use Workspace, Button Assignments. To set a new origin using Accudraw • Choose a drawing tool, e.g. the line drawing tool. • Tentatively snap to a location with respect to which you want to set the new origin • When you are satisfied that the tentative snap is in the correct position press the O

(Origin) key. The Accudraw compass will appear. • Move the cursor in the X or Y direction and key in the required offset in that

direction, do not press the enter key or any buttons • If you have offset X and wish to offset Y, or vice versa, do that now • When you are satisfied that the new origin is defined correctly press the LMB • Accudraw is now set at the new origin and is ready to continue to draw the selected

feature

49

That’s the theory, now let’s put it into practice : -

Tentatively snap to the bottom left corner of the cottage. Press O (for Origin). Accudraw is now waiting for you to define the position of the new origin, which will be 15 units to the right and 30 up. Move the cursor to the right and type in 15 (do not press enter, or a mouse button). Now move the cursor upwards, and type 30, your drawing should look like that shown above. Use the LMB to confirm that you are at the desired origin.

You should have successfully defined the start point of the left hand window, and can go ahead and draw the 30 square window in a similar way to that used for the main body of the cottage - but read the next paragraph first! If you make a mistake the RMB will reset the move, and you can start again. Accudraw remembers your last move !

50

You might have noticed that Accudraw remembers the last dimension used, forming a T shape at the end of the line, and locking onto that distance, when the cursor is in that approximate position. This can be used to advantage in drawing the window, as all of the dimensions are the same at 30 units. Repeat the procedure to draw the right hand window and the door. The roof is slightly more difficult. You will note that the angle that the sloping part of the roof makes to the horizontal is 45 deg. You can also see that the top of the roof is 40 units above the top of the main part of the building. Simple geometry tells us that the left sloping part of the roof must end 40 units to the right of its start point. This makes the central horizontal line at the apex of the roof 150 - 40 - 40 = 70 units long. Again using the Place Line command; snap to the top left corner of the rectangular main block. Use Accudraw to move 40 units to the right and 40 up. LMB to confirm. You will notice that Accudraw has swivelled round to align itself with the sloping line.

This is a handy trait in many circumstances, but not now. Press V, to cause Accudraw to align itself with the current View.

51

You can now continue to draw the roof, 70 across, and then 40 across and down.

Now for the chimney. Snap to the top right corner of the rectangular section of the cottage. Draw a vertical line 40 up, and a horizontal line 10 across to the left. The final vertical line is drawn as follows. Start the line as normal, locking Accudraw onto the vertical axis.

Now press N, to change to the Nearest snap, before moving to any point on the sloping roof line. Confirm with the LMB when Accudraw snaps to the correct point vertically beneath the start of your line. Both the ability to offset the drawing point and the Nearest Snap are very useful drawing tools. Erase your house and redraw it until you can do so without reference to the notes. Snappy Drawing The Nearest and Intersection snaps can be chosen by pressing N or I when the focus is in the Accudraw window. This feature can save you loads of time. If you learn nothing else about Accudraw then be sure that you remember this.

52

Try this. Draw two sloping intersecting lines. Move away from them and start to draw a third line. Press the I key after the Accudraw compass appears. You will have selected the Intersection snap allowing you to snap directly to the intersection of the two lines.

Start another line to the left of your sloping lines and move in the direction of them. Press the enter key, that will lock Accudraw to the horizontal. Now press N for the Nearest Snap and tentatively select one of the lines you are heading for. Press the left mouse button to confirm. You will have drawn a horizontal line that stops precisely at one of the sloping lines.

Don't just read this - do it!

53

Locking Accudraw On to an Axis We have already seen how Accudraw will lock to a vertical or horizontal axis when the Enter key is pressed. If you press Enter a second time the lock will be released, the Enter key toggles the axis lock on and off. You have also seen how you can pick up a dimension from somewhere else on the screen once the axis is locked, but let’s do this again so there can be no mistake. Draw a sloping line near to the bottom of the screen and then start another line somewhere near the top. Use Accudraw and the axis lock to draw vertical and horizontal lines that end at the same vertical or horizontal positions as the ends of the sloping line. The figure below shows what I mean.

Now draw two intersecting sloping lines near the bottom of the screen and repeat the above exercise, but chose the point of intersection as the required x or y co-ordinate position for the end of your horizontal or vertical line. You need to press I to select the Intersection snap.

54

Locking distances or an angle using Accudraw In the four examples that follow, the inverted V shape was drawn first, then the place line tool used to start a new line at the bottom left point of the V shape. The diagrams illustrate the way in which Accudraw can be made to lock onto a distance or angle associated with another point on the drawing, in this case the bottom right point of the V. Use the place line tool to draw an inverted V similar to that shown in the figure below.

Again, using the place line tool, snap to the bottom left hand end of the left hand sloping line. Now tentatively select the bottom right point and then press X. This will select the X lock. The line is constrained to end at the X co-ordinate position of the selected point. The dotted line indicates the locus of the end point of the line.

55

Proceed as before but this time the Distance lock is selected by pressing the D key. The line is constrained to be a radius of length the distance to the selected point. The Accudraw compass has changed from Cartesian to Polar co-ordinate setting, represented by the circular compass.

The Y lock is selected by pressing the Y key. The line is constrained to end at the Y co-ordinate position of the selected point

The angle lock is selected by pressing the A key. The line is constrained to be at the angle subtended by the chosen point.

56

Figure 13

Aligning The Accudraw Compass to Any Line It is often necessary to draw a line at a specified angle to an existing sloping line. You can align the Accudraw compass to any line in order to facilitate this. Draw any sloping line. Choose the Place Line command and snap to one end of your line. Now press R (Rotate) followed by Q (Quick). The Accudraw compass will pivot about the point that you have selected. Snap to the other end of the line. The compass is now aligned with the line, and ready to draw starting at the first point selected.

This is fine if you just want to draw only one line or element, but if you want to change the orientation of the Accudraw compass more permanently you need to use a slightly different approach. Pick the left hand end of the sloping line and then type RA (Rotate Accudraw coordinate system). Snap to the other end of the line. The Accudraw compass is now aligned to the line and will remain so until such time as you press V (align to View).

57

Accudraw and Smartline When you start to draw 3D objects, there is often a requirement to produce a profile of the part in 2D and then project or extrude the profile in the third dimension. A very useful drawing tool that enables you to do this is Smartline. In brief, Smartline allows you to combine lines, arcs, and blending radii in one continuous line to provide a single profile element.

58

Smartline is selected using the button shown and, when selected, displays the Place Smartline window also shown in that figure. For the current job you should check that the Smartline tool is configured such that :- Segment type - Lines Vertex Type - Sharp Rounding Radius - does not matter in this case Join Elements - X You can use Smartline in 2D as well of course, where it can replace, for example, the line and arc tools. You will find, however, that it does not have the same range of snaps available that the simpler tools provide, while not all of the normal line manipulation commands work with it. I would therefore recommend that you stick to the simple Place Line tool for 2Dwork. When drawing with Smartline you can undo the last point placement by pressing the Control (Ctrl) and Z keys simultaneously, this is normally written Ctrl Z. We will now draw the simple profile shown below using both Smartline and Accudraw.

59

We are going to start at the bottom left hand corner, and then draw the features up the sloping line, followed by the vertical line, and finally complete the drawing with the bottom horizontal line. The finished profile will be one complete profile element. Do not press enter, or the RMB, until the job is complete, or you will come out of the Smartline tool. If you make a mistake, use Ctrl Z to undo the last point, and try again. What follows seems a trifle longwinded. In practice it can be done very quickly, and I suggest that you practice until you can do the drawing without reference to the notes. Select Smartline and, after ensuring that Accudraw is active, click the LMB to choose a convenient place to draw the figure. Accudraw normally defaults to the Cartesian co-ordinate system, pressing the space bar toggles between Cartesian and polar co-ordinates. Try this now, and end up with the circular polar co-ordinates version selected. You will see that not only has the Accudraw compass become circular, but the co-ordinate readout now features a distance and an angle, rather than the X and Y of the Cartesian system.

60

Key in the length 50, do not press return. Press the down arrow key. This transfers the focus from the length to the angular co-ordinate in the Accudraw key in window. Type in the angle 30 and confirm with the LMB. Notice that Accudraw has now positioned itself at the end of the sloping line, and that it has aligned itself with the line. Press the space bar to return to Cartesian co-ordinates. Now draw the square cut out by moving the cursor in the direction of the first line, key in 15 and confirm with the LMB.

Now move at right angles in the direction of the next line (fig. 18), Accudraw has remembered the 15 dimension, and will lock onto that dimension when you are near to it. Accept the locked dimension with the LMB. Repeat the process for the third side of the square, and then for the next section of the sloping line. The next task is to draw the semi circle. Go to the Smartline window and change the Segment type from lines to arcs. Now move the cursor in direction of the arc centre and key in 10, the position of the arc centre, accept with the LMB. Move a further 10, Accudraw will lock to 10 when you get near it, and accept the end of the arc. Change back from arcs to lines. Draw the final section of the sloping line, which is also 10 long, accepting with the LMB.

61

Now we want to change the orientation of Accudraw away from that of the line we have been working along and back to that of the view, i.e. normal Cartesian co-ordinates. Press V to change the orientation to that of the current view. The Accudraw compass swivels round to line up with the co-ordinate system of the view. We now have to draw the vertical line, but we don’t know its length. Fear not, Accudraw will assist here. Move the cursor to the bottom of the sloping line and select that as a tentative point. Press Y to tell Accudraw that you have selected the required Y co-ordinate for your line. A little cross should appear alongside the Y co-ordinate in the Accudraw window, and when you move away from the tentative point you should find that your line is now constrained to the required Y position. Move back until Accudraw locks to the vertical position and accept with the LMB. Finally move horizontally back to the start point and use the tentative keypoint snap to lock onto it. Accept with the LMB. RMB to finish the job. Now erase it and draw it again ! Do this until you can draw the figure without reference to the notes. Clever things with Smartline Now change the Smartline Settings such that :- Vertex Type - Rounded Rounding Radius - 5 Draw the figure again and see what you get ! You will note that Smartline has automatically provided circular fillets of radius 5 at the junction of the lines. Figure 19 shows this.

Figure 19

62

I suggest that you spend a bit of time with Accudraw and the Smartline command drawing various profiles, until you feel that you have mastered the technique. Once you are familiar with Accudraw you will not want to switch it off, as it will become an invaluable drawing aid. You may prefer to use Smartline rather than the ordinary place line command, but remember that not all of the commands that apply to the place line tool are available to Smartline. For that reason I would recommend that you do not use it in 2D drawing. Accudraw – Key Points A few key things to remember about Accudraw:- • the space bar toggles between Cartesian and polar co-ordinates • pressing V restores the orientation of the compass to the co-ordinate system of the

view • you can move between the two Accudraw text input windows using the up and down

arrow keys • you can lock onto a co-ordinate position by tentatively selecting it and pressing the

X, Y, D or A keys • to change the Accudraw origin, tentatively snap to a known point, press O and then

enter the co-ordinates of the new origin relative to the known point • You can change the snap, for the next operation only, by typing C, I, N or K when

the focus is in the Accudraw window Summary Having completed the lesson you should be able to:- • Use Accudraw to assist in drawing • Use Smartline to produce complex profiles formed from a single element Bryan Attewell 02 August 2005

63

Self Assessment Questions 1) Draw the figure Q1 using Accudraw Hint - use Accudraw to set the origin of the smaller rectangle.

Figure Q1

2) Draw the figure Q2 using Accudraw

Figure Q2

Hint - Draw the triangle first, then align the accudraw compass with each one of the sloping lines in turn to construct each rectangle. You will have to start in polar oordinate mode and then transfer to rectangular coordinates. 3) Figure Q3 shows the end view of an aluminium alloy extrusion that is to be used as a track for the sliding doors of a fitted wardrobe system. The thickness of the material is 3 mm, while all radii are 1 mm. Draw the profile as a single element using Accudraw and Smartline.

64

Figure Q3

Bibliography [1] K.R. Little. Inside Accudraw. Adage Books. 1997 ISBN 1-885315-33-3 [2] N. Addison. Microstation 3D by Examples 2nd Ed.. Pen and Brush. 1997. ISBN 0 9586831-1-5 [3] Microstation 95. User’s Guide. Bentley Systems. 1995.

65

CAD Lesson 4 - More Tricks Introduction This lesson builds upon the previous one where you learned a few simple drawing commands. In this lesson you will be learn some more useful commands and find out how to produce a print of your work. Aims At the end of this lesson you should be able to:- • zoom and pan into the section of your drawing that you want to see. • draw lines that are parallel to existing lines • trim and extend lines • use more snap commands • mirror, copy and move sections of your drawing • add text to a drawing • divide an element into a series of equal sections • produce a standard drawing border • use the axis lock Drawing Lines Parallel to Existing Lines It is often useful to be able to draw a line or a curve parallel to another one, offset by a fixed distance. Microstation allows you to either move your first line, or copy it to the new location. First find the Manipulate tool bar from near to the bottom right of the main tools menu on the left of the screen.

The move/copy parallel to tool is selected using the button containing two parallel wavy lines as show. Having selected the Move/Copy Parallel tool then a new window should appear.

66

The most frequently used form of this command is copy parallel, and to achieve this it is necessary to click within the Make Copy box. Microstation will invite you to select an element to move/copy. Experiment with this now. You will see that first click of the left mouse button identifies the element to be copied by highlighting it in red, and makes a copy to one side or the other. Moving the mouse from one side to the other causes the copy to move accordingly. When you are satisfied that your copy is in the required position press the left mouse button to confirm. Press the right mouse button to terminate making copies of the selected element. It is most useful to be able to offset elements by a known distance. This is achieved by clicking in the Distance box and entering the required distance, e.g. 20 mm.

Now that the offset distance has been set to 20 you can select which side of the element to offset by moving the mouse. Try that now. You may find that your drawing has been made to such a scale that the 20 mm offset is off the screen, or very close to the original element, in those cases change the distance to a more appropriate quantity. After selecting the element to copy, each press of the left mouse button causes a copy to be drawn, while the right mouse button causes the process to cease.

Original drawing

67

After copying parallel

In the sketch above I have shown the result of offsetting the line and the circle by a fixed amount. Try to do the same. Trimming and Extending Lines

Erase all elements of your drawing and draw that shown above – ignore the characters just draw the lines and circle. We are next going to use Microstation’s trim and extend commands. In the first instance we will trim the two lines intersecting at X so that they no longer extend above X. We will then trim the line through the circle so that it remains as a chord of the circle only.

First choose the Trim Element tool as shown in fig. 10. I intend to trim the line BA first, so the cutting element will be the line CD. Microstation asks for the information, Trim Element > Select Cutting Element. Select the line CD when it will be highlighted in a different colour to that of the active level. The program now asks us to Accept, Identify, Trim Element/Reject. Click onto the part of AB above X. Confirm with a further click of the left button. Repeat the exercise using BX as the cutting element, and trim CD to CX.

68

Finally select the circle as the cutting element and trim each end of the line FG. Your drawing should now look like that below.

It is possible to nominate more than one line as the cutting element. Consider the diagram below: -

We can choose both of the lines BB and CC, and cut out the central section of the line AA. Use the Element selection tool (looks like an arrow head) to select line BB, and then hold down the Control (Ctrl) key while selecting line CC. Both lines should be coloured differently at this stage.

69

Now click on the Trim Elements tool and then pick a point on the central section of AA. The section between the lines BB and CC should be deleted.

Extending Elements Perhaps the opposite of trimming is extending. It is certainly very useful to be able to extend elements in drawing. I intend to demonstrate this by extending the chord of the circle until it touches one of the sloping lines above.

70

First choose the button to Extend an element to intersection, shown highlighted above. You will be invited to select the element to be extended. Do this by clicking on the chord of the circle. Next click onto the lower sloping line, the element that you want to extend to. Finally accept that point when the line will be drawn as shown below.

This extend element to intersection command can also be used to trim lines. Pick the chord within the circle and then the circle itself. The line will be trimmed to the intersection of the chord and the circle.

Mirror We are going to draw the shaft shown below. You will note that it is symmetrical about both the x and y axes. As a result of this we only need to draw one quarter of the shaft, as we can then use Microstation’s MIRROR command to complete the task. The MIRROR command will produce a mirror image of a section of a drawing.

71

Open file des1.dgn and save as shaft.dgn. Start by drawing one quarter of the shaft as shown below. Draw it using straight lines, and then use the circular fillet tool to finish the job. Don’t attempt to draw the diagonal lines representing the flats at this stage.

We are now going to produce a mirror image of this section about the x-axis. The steps are as follows:- • tell Microstation what part of the drawing we want to mirror. In this case all of the

drawing. Choose the draw fence button and draw a fence right round the drawing. • now choose the Mirror tool and select Make Copy and Use Fence in the mirror

window.

72

• make sure that the parameter Line is chosen from the Mirror About selection, and Inside is chosen from the Use Fence selection

• observe the instruction, Mirror Fence Contents About Line (Copy)>Enter First point on mirror line (or reject).

• pick each end of the horizontal centre line in turn, and then press the right button to end the command.

• re-select the draw fence command, which will cause the existing fence to disappear • the result should appear shown below

Now draw the diagonal lines to represent the flats on the left hand end of the shaft, before using the mirror again to draw a mirror image about the right hand vertical centre line. Don’t forget to press the right mouse button to complete the mirror command.

Don’t worry about adding the dimensions at this stage.

Using the view commands The view commands are displayed at the bottom of the drawing window

but you might want to open a larger window showing these commands using Tools, View Control We can use your last drawing to practice some of the viewing commands. It is essential when using CAD to use the view commands to ensure that you always have a large enough image to be sure that you are drawing accurately.

73

The window above shows the complete set of view control commands. I have selected the View Window button. You try that now when you will see the command Window Area>Define first corner point Choose to zoom in on the left hand end of the shaft by picking a point above and to the left of the required area and then a second point below and to the right of it. You should now see an enlarged view of your choice. Pick the Undo View command button (anticlockwise pointing arrow, third button from the right) to return to the original view. Try zooming to different windows. If you get stuck pick the Fit View button (looks like a mountain range) to restore a view of your entire drawing.

You can see an enlarged or reduced view by choosing the Zoom In or Zoom Out buttons - they look like magnifying glasses containing a + or - respectively. Try them now.

Finally we can try the Pan command button. This looks like a large arrow. Using this command you can drag your view in any direction. Try it now.

Restore the view using the Fit View button. When you erase sections of the drawing you may find that some of the elements that you want to remain are partially erased. You can restore the view using the Update View button, it looks like a paintbrush.

74

Copying and Moving It is possible to copy or move either individual elements or groups of elements. The sequence of events is as follows:- • identify an element or elements (using a fence) to be copied or moved • select either the Copy or Move tool from the Manipulate menu (fig. 20) • identify a data point on the element or group of elements to act as the origin • identify a second data point to which the move or copy will be made.

The copy tool is shown selected, the move tool is that to its immediate right.

The drawing above shows a view on a cover plate held in place by four M8 studs, nuts and washers. We will draw this view by following the steps:- • draw the cover plate

75

• draw the centre lines of the studs • draw one nut/washer/stud assembly • copy the nut assembly onto the four positions on the cover plate. Open the file des1.dgn and save as cplate.dgn. Start by drawing the cover plate as a rectangle. Then draw the centre lines - I suggest that you use the Copy Parallel tool to help construct the centre lines. Finally use the Circular Fillet tool to round the corners of the plate. Next you can tackle the nut and washer. I suggest that you draw it off the view of the cover plate. You will find a useful chapter in your Manual of Engineering Drawing entitled Nuts, bolts, screws and washers. In that chapter are given the dimensions of most common fasteners, along with a set of approximate sizes for constructing a generic nut. These last values are very useful as they are adequate for most purposes. Only in the circumstances of having to fit a fastener into a very tight space, or possibly designing a spanner, should you need to consult the detailed tables of exact dimensions. The approximate dimensions are all based upon the nominal thread size D. Thus the hexagon has an across the corners dimension of 2D. We don’t need to know the height of the nut in this case, given as 0.8D. Our nut has nominal size M8 (metric 8 mm), so the hexagon is inscribed in a circle of diameter 16.

Find the Polygons slide out tool box from the main tool box. Choose the Place Regular Polygon tool, specify 6 Edges, a Radius of 8, and the Inscribed Method. Draw the polygon to the side of your cover plate. It is conventional to line the hexagon up with the vertical or horizontal axis.

76

The figure above shows the stages in drawing the nut and washer. You will only be drawing the nut once of course. After drawing the hexagon, choose the diameter button and select to fit by diameter. Pick up the key points that are the mid points of the bottom and top lines of the hexagon to draw the circle inscribed within the hexagon. Next draw the washer at a diameter of 2D or 16 mm, and a smaller circle of diameter 7 mm. Finally draw the arc representing the major diameter of the thread at 8mm.

The next task is to copy the nut assembly to each of the four locations on the cover plate. Draw a fence around the nut and then select the Copy button. Make sure that Use Fence is selected on the copy pull down menu. Pick the circle centre as the origin for the move and then select the intersection of the centre lines for the position of the copied nut assembly (use the Intersection snap). You can copy the assembly to the remaining three positions to obtain a drawing like that shown. Save your drawing. A Standard Drawing Border All engineering detail and assembly drawings should be displayed on a standard drawing sheet that should include a projection symbol, and normally includes the number and title of the part, the material specification, the name of the draughtsperson, and the date on which it was released. A useful addition is a grid system of letters and numbers that allows a small section of the drawing to be defined, perhaps during a phone conversation. Different companies have their own house styles of drawing border, and I have no objection to your using your company standard. BS308 specifies standard sizes of drawing paper as follows:-

A4 210x297 A3 297x420 A2 420x594 A1 594x841

A0 841x1189

We must allow space for the plotting device to grip the paper, a 10 mm border should be sufficient.

77

I will talk you through the drawing of an A3 size drawing frame and it will then be up to you to draw your own for the other sizes. The finished product is shown overleaf as fig 31. 1. Open your des1.dgn file and save as a3.dgn 2. Draw a rectangle 277 by 400. 3. The title block is 80 wide and each section is 20 high. Use the Accudraw and the

copy parallel commands to construct it. Divide the lower section into two. 4. Copy parallel the top horizontal and left vertical lines by 5 to begin to produce the

grid reference boxes. Trim the two offset lines where they cross at the top left hand corner of the drawing.

5. Draw the projection symbol in the bottom right box of the title block. Note that the

relative dimensions of the parts are given as Fig. 4.8 in the Manual of Engineering Drawing. I have drawn a first angle symbol, you may prefer to draw a third angle symbol, it does not matter provided that you are consistent. Draw the projection symbol anywhere on the screen, only when it is complete move it into the space within the title block as shown below.

78

79

6. Now enter the text within the title block. Use the text entry button fig. 25. You will

have to open up the lower section of the Place Text window by clicking on the small arrow head at the bottom right of the window.

Figure 25 I set the text height and width as 3 mm, which seems to be about right for this job. Enter the text in the text editor window (fig. 26) and then place it carefully on your drawing using the mouse. If you are not satisfied with the placement, use the move command to shift the text.

Figure 26

Complete the title block in this way.

80

7. The final task is to complete the reference grid. Microstation provides a useful

command to divide a line into an equal number of sections. It is called Construct Points Between Data Points and the appropriate button is shown in fig. 27. If we accept the default point type, which is a zero length element, then we will not be able to see the points that have been generated. One way round this is to change the level to type Construction before carrying out this command, so that the points will be drawn on a different level, and in a different colour to the remainder of the drawing. I have elected to choose ten points in total, so as to give nine equal sections along the length of the element.

Figure 27

Use this command to divide the top side of the rectangular drawing frame into nine sections. Choose each end of the lower of the two horizontal lines to indicate the element to be divided.

Now switch off the main drawing and centre levels, and use the Fit View button to zoom into the points that you have drawn at the left hand end of the line.

81

Use the Place Line command to draw two 5 mm long vertical lines from each of the leftmost two construction dots. If you set the angle and length of the line as shown it will be a simple matter to draw each line in turn.

Don’t forget to switch off the Length and Angle boxes when you have drawn the two 5 mm lines. Having drawn the two lines, draw a fence around them and use the Change Element Attributes button to change the construction lines to lines on the main drawing level.

The next part of this job is to insert the letters and numbers in the centres of the boxes. I decided to draw a construction line between the midpoint of each of the two 5 mm lines

82

to enable me to fix the centre spot. The letter A can then be entered using Place Text and the default keypoint snap. You may have to change the default angle from 90 to 0 degrees to avoid having the letter lying on its side.

Once the construction line has been erased we can use the copy command to replicate the central character A and the rightmost 5 mm line along the top of the drawing border.

Copy both of these letters in the same way to obtain a total of 4 instances. Then copy the four to give eight, and finally copy the last A only to obtain the full nine. We can now edit the characters to give a series from A through to I using the Edit Text button.

83

Now repeat the operations above to obtain the vertical grid of numbers to the left of the drawing. I used eight points to give seven grid boxes..

We expect that you will always submit engineering drawings enclosed by a drawing frame, although the particular detail of the frame is up to you. N.B. In a later lesson you will learn that it is possible to drop a drawing border onto a finished drawing, scaling the border to fit. Always work this way, don’t start with a border and try to scale your drawing to fit.

84

Using the Axis Lock You might remember that when we configured your drawing DES1 initially we decided to switch the grid lock off. There are other locks, perhaps the most useful of them being the axis lock. When the axis lock is selected all of the elements that you draw will line up with the horizontal or vertical axes. The axis lock comes into its own when you are drawing orthogonal views and want to project lines between the views, it is also useful if you want your nuts and bolt heads to be aligned etc. The most convenient way to access the axis lock is by the little lock symbol normally found near to the bottom of the screen. Now there are occasions when this symbol is overwritten by Microstation, but it can always brought back into play by a mouse click in its approximate location.

Try it now, you should see a pop up menu which includes the Axis and Grid locks. Select the Axis lock by clicking on the word Axis. The menu will disappear and a little message Locks= AX, should appear. .

Click in the position of the lock symbol and switch the Axis lock off, but remember this useful feature for future reference. Self Assessment Questions 1) Produce an A4 sized standard drawing frame. I would suggest that you use the same size of title block etc that were used in the A3 example in the text. You might decide to provide fewer grid positions. If you have access to a CAD plotter able to accommodate larger sizes of paper then it might be a good idea to draw some larger borders as appropriate. 2) Draw the shaft shown in fig. Q2. Do not try to include the dimensions.

85

Fig. Q2

Hints:- • Use the Help command to determine how to automatically Construct Chamfers. • Use the mirror command where possible. • Assume that the minor diameters of the 10 and 20 mm threads are 8 and 17

respectively Summary Having completed this lesson you should be able to:- • zoom and pan into the section of your drawing that you want to see. • draw lines that are parallel to existing lines • trim and extend lines • mirror, copy and move sections of your drawing • add text to a drawing • divide an element into a series of equal sections • produce a standard drawing border • use the axis lock Bryan Attewell 02/08/2005

86

CAD Lesson 5 - Projected Views and Ellipses

Figure 1 Figure 1 shows the basic use of construction lines in producing four views. Note that a different layer has been used for the construction lines. Using a separate layer for construction lines has three advantages: - 1. The lines can be of a different colour and thickness to the main drawing lines, so

you are unlikely to confuse the two sets of lines. 2. It is possible to switch the construction line layer off when the time comes to plot

the drawing. 3. You can isolate the construction line layer, which means that construction lines can

be easily deleted, without fear of erasing the main drawing lines. In the example above, the proportions of the top left view have been obtained entirely by the use of construction lines. Note the use of a line drawn at 45 degrees to turn the lines from the plan view into the end elevation.

87

In many cases it is quicker to avoid using construction lines, but you should be aware of the technique for those occasions when there is no alternative. Circles on Sloping Surfaces Circles only appear truly circular if viewed head on. A circle projected onto a sloping surface will appear distorted in the direction of the slope and has to be drawn as an ellipse. Referring to figure 1 above, in the plan view and end elevation the semi circular cut has to be drawn as an half ellipse. The width, height, and centre of the feature are defined by construction lines while the ellipse feature of the CAD program takes care of the rest. Auxiliary Projection Note that the only true view of the semi-circular cut occurs on the projection of the sloping surface at 90 degrees to the surface as shown in the top right view. This is termed an auxiliary projection. Rather than use construction lines for auxiliary projections you can make use of the Accudraw Rotate Axis command – demonstrated in an earlier lesson. In order to obtain accurate dimensions off features on sloping surfaces it is normally necessary to draw an auxiliary projection. Drawing arcs and circles to touch particular points on the drawing It is often necessary to draw arcs between particular points, and construction lines can be used to assist in this process. If you know the radius that you want to use, then the following simple rules should be followed: - • If the arc is to pass through a point, then the centre of the arc will lie on a circle

whose centre is at the point and whose radius is equal to the arc’s radius • If the arc is to touch a line, then the centre of the arc will lie on a line drawn parallel

to the original line whose perpendicular distance from the line is equal to the arc’s radius.

• Given that the arc must touch two points, if we draw the construction circles or lines as appropriate, then where the two constructions intersect, we have an arc centre point that satisfies the requirements of both points.

A few graphical examples should make this clear: -

88

Figure 2 In figure two it was necessary to draw an arc which went through the intersection of the short horizontal and vertical lines, and was tangential to the long horizontal line. The arc radius was chosen to be 20. Two constructions were drawn, one a line parallel to the horizontal line and offset by 20, and the other a circle whose centre is at the intersection, and whose radius is also 20. There are two possible centres for our arc, only one of which is shown, at the intersection of the two construction elements. The required arc could be drawn as a circle, centre that intersection, and radius 20 and then trimmed to leave the arc, or the arc drawn directly tangential to the longer horizontal line.

89

In the figure above we have a line and a large circle. It is necessary to draw radii blending the circle to the line. A radius of 10 has been chosen for the blend radii. Two construction elements are drawn, one a straight line, the other a circle. They are both obtained by offsetting by 10. The blend radii have centres at the intersections of the construction elements. The drawing is then trimmed to provide the blend radii. You might also try the fillet command!

Figure 4

In figure 4 we have two circles radius 10 and 20. They could represent the pitch circles of gear wheels. It is necessary to draw a third circle, mutually tangential to the first two. The radius has been chosen as 10. Construction circles are drawn offset by 10 and the intersections give two possible locations for the centre of the third circle. Conclusion Construction lines can assist in CAD drawing. You don’t have to use them if you can think of an alternative way of getting around the problem, but in some cases they are essential. In many cases Accudraw provides a faster alternative. It is usually better to use a separate layer for construction lines, using a different colour to the main drawing lines. Don’t forget the CAD commands that avoid the use of construction lines, for example the FILLET command that will automatically provide a fillet radius between two elements of your drawing.

90

CAD Lesson 6 - Arrays, dimensions and tolerances Introduction You should now be reasonably confident at two dimensional drawing using Microstation. There are a few useful techniques remaining to be mastered, and I will be expecting you to make more independent use of the built in Help system during this lesson. It is frequently necessary to make numerous copies of a component or sections of a component, e.g. to represent a series of fastenings around a part. Microstation provides the ARRAY command to handle this. This command can handle either circular repetition, e.g. the spokes of a wheel, or linear, e.g. sleepers on railway track. This lesson introduces the array command. So far you have relied upon me to provide all of the dimensions. In this lesson we will explore some of Microstation’s dimension commands, and find out how to apply tolerances to dimensions. Aims At the end of this lesson you should be able to:- • use the array command to generate multiple copies. • dimension components • apply tolerances to dimensions Using the Construct Array command Use the help system to look up the Construct Array command. Determine the difference between polar and rectangular arrays. We will use the Construct Array command to draw the railway wheel shown in fig. 1. First draw the five circles representing the hub, rim and flange. Next draw the top vertical spoke. I drew a construction line between the top quadrants of the inner and out circles to represent the centre line of the spoke, then used the Move Parallel command to copy each side of the spoke at a distance of 15 mm. The spoke was completed using the Construct Circular Fillet tool. Note that the fillet at the top is of a larger radius than that at the bottom. The time has now come to use the Construct Array command in order to copy the spoke around the wheel. Fig. 2 shows the relevant command button, and the corresponding pop up window. Now the spoke consists of a collection of elements, two lines and four radii. We need to indicate that they are the components to be copied by the array command. This is achieved by drawing a fence around them. Do that now, be careful to ensure that your fence does not include any other complete element.

91

You should also ensure that the correct parameters have been picked and entered into the Construct Array window, i.e. • Array Type - Polar • Items - 15 • DeltaAngle - 24.0 • Rotate Items - x • Use Fence - x It is unfortunately necessary to tell Microstation not only how many items will be in the array, but also the angular distance between them.

Figure 1

92

Figure 2 Now pick the array button, and select the centre of the circle as the point that will be the centre of the array, and Voila - there are 14 copies of your original spoke. You will appreciate that this is a very powerful and useful command, note in particular that the number of Items chosen includes the original; it does not make 15 copies, only 14. I would suggest that it would be useful for you to un-do that last command (anti-clockwise facing arrow at the top of the screen) and try it again. The Rectangular Array As well as providing a polar array, Microstation also has available a rectangular array. I have used a drawing of a wooden banister spindle to illustrate this. Draw the spindle as shown in fig. 3. Being an old hand now you will realise that the component is symmetrical about the x and y axes and that you will only need to draw one quarter of it. The only tricky bit is the elliptical form of the centre section, and that is easily dealt with using Place Quarter Ellipse, see fig. 4.

Figure 3

Figure 4

Having finished the drawing of the spindle you can now rotate it (fig 5) before constructing a rectangular array (fig 6). You will need to draw a fence around it for both of these operations.

93

Figure 5

Figure 6

The finished drawing is shown in fig. 7. Lines have been added to the top and bottom to represent the floor and top rail.

94

Figure 7

Dimensioning Drawings Microstation provides a wide range of dimension commands, as illustrated by fig. 8. One very useful feature is that of associative dimensioning, where, if the size of component is modified, then the resulting dimensions will automatically change with it. For the work that we will be doing, only a sub set of the commands will be needed. Perhaps the most frequently use one is Dimension Size With Arrow, as shown selected in fig. 8.

Figure 8 Note that in fig. 8 I have set the Alignment to Drawing. This is the most generally useful setting, but you might experiment with the other options.

Setting Text Size

95

Before starting to dimension it is wise to set the text size to an appropriate value. The actual size chosen will depend both upon the size of the component drawn and the size of the eventual hard copy. If we could be sure that all our drawings would be plotted at a scale of 1:1, then a text size of 3 mm would be satisfactory, but if we wish to scale the drawing when plotting - the most common situation in my experience, then different sizes will be needed. Consider a drawing of a lamppost that is 7 m tall. If we were to draw that to size, chose a text height of 3 mm and then plot the drawing on A4 paper, the dimension text would be too small to read. In that instance a more sensible size might be 15 or 20 mm. On the other hand if we were drawing the circuit detail for an in the ear speaker, then we would want to amplify the drawing to allow it to be read, the selected text size should be 1 mm or less. To change the text size do the following:- • pick the Element pull down menu • select Dimension • select Text in the Dimension Settings window (fig. 10) and adjust the text size

accordingly. Microstation recommends that, for best results, the Width should be set to three quarters of the Height, but this is not critical and perfectly acceptable text is produced if they are both set to the same value.

Figure 10 OK now lets try to dimension a drawing. Load in the drawing of the shaft that you made in lesson 2, shown as fig. 11.

96

Figure 11

Let’s do the easy bits first. The key horizontal lengths are all taken from the vertical centre line, with sizes of 60, 42 and 18 mm. Use the Dimension Size with Arrow command with settings as shown (fig. 8). Now do this:- • Select level 5, the dimensions level. • Use tentative snap to select the top left corner of the rectangular square at the left

hand end of the shaft. Confirm your selection. • Move the cursor sufficiently high above the shaft to show where the 60 mm

dimension will be placed. Press the left button. • Tentatively snap and then select the top end of the vertical centre-line If all has gone according to plan you should see the 60 mm dimension correctly in place. How, you may ask, does Microstation differentiate between vertical and horizontal dimensions? Consider, for example, the simple case of a sloping line. It is possible to dimension the projection of the length onto both the vertical and horizontal planes. Microstation is guided as to the particular dimension required by the position that you decide to input when asked to Define the length of the extension line. This may be made clear if we remember the compass and point accordingly:- • horizontal dimension line above the view - move North • horizontal dimension line below the view - move South • vertical dimension line to the left of the view - move West • vertical dimension line to the right of the view - move East The software will invite you to enter a string of dimensions. If, as is usually the case, you do not want to do this, it is necessary to reset the command with the right mouse button. Try this now for yourself, draw a line sloping at about 45 deg., and provide four dimensions, above, below and to each side.

97

Back to the shaft in fig. 11. You can now dimension the width of the raised collar (4 mm), and the height of the end rectangular section (12 mm). Dimensioning Diameters, the letter ∅ Now for something a little different. It is necessary to dimension the circular parts of the shaft, and the British Standard requires that the dimensions of diameters are preceded with the Greek letter ∅. Microstation will automatically insert a ∅ if a full diameter is shown on the screen, and we choose a dimension diameter command. In the case of our shaft that view is not shown. We therefore have to instruct the programme to insert a ∅ when dimensioning the circular sections. For this purpose we need to refer again to the Dimension Settings window, and select the Tool Settings option.

Figure 12

Note that in fig. 12 that the Prefix option has been set to a ∅. Now dimension the ∅18 and ∅26 diameters at the right hand end of the shaft. Don’t forget to switch the Prefix ∅ setting off before drawing any more dimensions. Conventional Diameters and Radii These features are handled easily using the Dimension Radial command as shown in fig. 13. You can set the Mode to Radius or Diameter, with internal or extended dimension lines.

98

Figure 13 Now dimension the two radii on the collar, one at 2 mm and the other at 1 mm. Changing the style of dimensions If you find that the applied dimension is not to your liking, it is possible to change it to represent the latest settings in the Dimension Settings window.

Figure 14

Fig. 14 shows the Change Dimension to Active Settings button selected. The technique is as follows:- • make the necessary changes to the Dimension Settings window • select the Change Dimension to Active Settings button • pick the dimension to be changed. You may find that the dimension lines for the ∅18 have been drawn outside the projection lines, and so cut through the projection lines for the ∅26 dimension. It is possible to force the program to use dimension lines on the inside of the projection lines. Use the Dimension Settings window and choose the Terminators option. The

99

default condition calls for the Automatic placement of the terminators, but you can change this to Inside. Now apply Change Dimension to Active Settings and click onto the ∅18 dimension when it should change to internal dimension lines. Reset the Terminators option to Automatic placement. Circles and Leader Lines Draw the circular cover plate shown in fig. 15. You can either use the array or copy commands to place the nuts and washers into position. A lazy, but intelligent, person might revert back to the exercise in lesson 3 and draw this cover plate alongside the rectangular one drawn then, and so avoid having to draw the nut again.

Figure 15

In figure 15 I have experimented with the dimension commands and set-up to obtain different styles of presentation. The 80 mm diameter dimension has been obtained using the standard Dimension radial tool, but with the Mode set to Diameter Extended. The style of the 60 mm dimension is a little more tricky to obtain, here I used Element, Dimensions, Location, Manual, rather than the default Automatic. I have also toggled the Axis lock to allow me to write the dimension text horizontally, after positioning the text in the approximate required position without the axis lock. Don’t forget to reset the dimension setting to Automatic, if you try this. The 4 x M8 nuts and washers message was placed at the end of a leader line. To apply a leader line use the Place Note button as shown in fig. 16.

100

Figure 16 When this has been selected both the Text Editor and Place Note windows should appear (fig. 17). Set up the Place Note window with Type set to Multi Line, and the Generate Leader box selected. Type the message “4 x M8 nuts and washers” into the Text Editor window. If all has gone according to plan you should see the message:-

Place Multi-line Note>Define start point Tentatively select a point on one of the four nuts, and then select where you want the message to go with the mouse.

Figure 17 You may find that an unpleasant + sign, together with an unwanted number, has appeared on your drawing, overwriting part of your message. If that is the case click once in the top left hand corner of your current view window and select View Attributes, fig. 18. Switch Text Nodes off, and Apply. Get rid of the View Attributes window.

101

Figure 18

Leader Lines Pointing to Messages Containing Symbols The section on leader lines and messages above is fine if your message contains only standard alphabetic or numeric characters. It is often a requirement to incorporate symbols however, e.g. • 6 Holes equally spaced ∅10 • Machine taper at an included angle of 15° We have therefore to find a way to insert the frequently used symbols ∅ and °. Unfortunately this is not a trivial task in Microstation. The standard Engineering Font does not incorporate the ∅ symbol, so we must change Font to carry out this exercise. Font No. 100 ANSI_SYMBC does contain the symbols, but does not offer lower case characters. Therefore to insert symbols it is necessary to write the message in upper case characters. To change font select Element, Text, when the window shown in fig. 19 will appear. If you click on the font name you will be presented with the range of possibilities, select 100-ANSI_SYMBC.

102

Figure 19

Draw the plate shown in fig. 20.

Figure 20

To incorporate the message “12 HOLES ∅8” it is necessary to use the place note tool (fig. 16), and to use a trick within the text editor. If you type your text in the editor in lower case all will appear well until such time as you place the text on the drawing when it will appear as a string of symbols. This is because in Font No. 100 the lower case characters have been replaced by symbols. You must therefore type all alphabetic characters in upper case. When you want to insert a symbol it is necessary to inform the program by typing a backslash \, followed by the ASCII (numeric) code of the symbol. The code for ∅ in font No. 100 is 110, so \110 produces a ∅.

103

Fig. 21 shows how to enter the message “12 HOLES ∅8”

Figure 21

Arguably the three most useful symbols are °, ∅ and ±. The relevant ASCII codes corresponding to the ANSI and Engineering fonts are:- ° ∅ ± ANSI 94 110 126 Engineering 94 - 127 You may prefer to use upper case characters throughout in your engineering drawings when you might adopt font 100 as your standard. Font number 106 INT_ISO_EQUAL offers both upper and lower case characters and has available the three useful symbols, unfortunately it does lack some of the clarity of the two fonts previously discussed. In that font the mapping is as follows:-

° 176 ∅ 180 ± 177

Actually the drawing standard prefers that upper case letters be used, so that text remains readable when drawings are reduced, but it does not exclude the use of lower case characters. Personally I find a combination of lower and upper case characters much more user friendly.

Applying Tolerances To Dimensions Tolerances can easily be applied to individual dimensions by selecting Element, Dimensions when the Dimension Settings window appears, fig. 23. Select Tolerance then switch on Tolerance generation by clicking in the box. Set Attributes Type to Limit and key in the Upper and Lower limits. The use of any linear dimension

104

command will now result in the BS preferred form of tolerance showing both the lower and upper sizes.

Figure 23

Try this now by applying a toleranced dimension to the spacing between the outer and centre holes in your drawing of a plate (fig. 24).

Figure 24

Of course it is good practice to apply an overall tolerance to a component, to avoid having to tolerance each dimension separately. An appropriate note should be added to the drawing as in fig. 25. Here the Place Text tool is used (fig. 24, lesson 3), and the clever trick of inserting an ASCII code described above is employed to obtain the ± character.

105

Figure 25

Try this now. Be sure to press the Return key at the end of each line to ensure that the message appears on three separate lines. I had to increase the Line Spacing, (select Element, Text) to obtain a good standard of presentation. Limits and Fits It makes good sense to employ standard limits and fits whenever possible (Refer to Chapter 19 of the reference book [1]). Here the drawing standard prefers us to cite the nominal size, the grade of fit, and the permissible range. I have not been able to find an automatic dimensioning tool to achieve this. It seems that the only way is to draw the text and brackets. Consider a ∅ 50 hole, the H7 fit calls for a range from size to +0.025. To produce the text below (fig. 27) I used the Place Note tool set to Right Justification (fig. 26).

Figure 26

106

Figure 27 Problems in moving dimensions When a dimensioned object is copied or moved, the dimensions do not always move as expected. This is due to the dimension extension lines being associated with, or tied to, particular points on the drawing. There are a number of ways around this. 1) Switch off association lock before dimensioning Select the Settings pull down menu, followed by Locks. Ensure that there is no tick alongside the word Association. Using associated dimensions means that, if a dimensioned element is modified, the dimensions will automatically update. Dropping the association lock means that this facility is removed. It may be that you consider this a worthwhile sacrifice, and want to permanently modify your design file, des1.dgn accordingly. Unfortunately, switching the association lock off does not remove the association from previously drawn dimensions. If you have had association lock on, have made the drawing and completed the dimensioning, but require to move the view, then all is not lost. There are other ways around this problem, although all involve a degree of hassle. The moral of the tale is that you avoid dimensioning until you are pretty confident that the views are in the right places.

107

2) Use Drop Association Select the Tools pull down menu and the Drop toolbox. According to the instruction manual, the Drop Association tool, looking like an open lock, is the one to use.

To use this tool, it is necessary to identify the dimension extension line that is associated with an element. In use, the following messages appear at the bottom of the screen. When the tool is first selected Drop Association>Identify element When picked, the dimension changes colour. You are invited to confirm your choice with the LMB. Accept/Reject (select next input) There are two possible outcomes Not an associative point. Normally seen if you have already dropped that associative point, or if it were not an associative point in the first place. Association dropped. When the association is successfully dropped. In practice, this command seems to take quite a few key presses to obtain the desired result. I would recommend selecting all of the extension lines until the message Not an associative point is consistently returned. This is particularly important where several dimensions share a common extension line. What is required, but not provided, is a device that will allow the association to be dropped from a group of dimensions, e.g. by using the fence. 3) Use Drop Dimension Element

108

Also featuring in the Drop toolbox is Drop Dimension Element. This is the tool that does the business more quickly. Be warned, however, that dropping the dimension into its elements, i.e. arrow heads, text etc., makes it a nightmare to deal with if further editing is required. You can, of course, isolate the dimension layer and deal with the bits that way. 4) Delete the Dimensions You might prefer to move the view and then delete and restore the faulty dimensions. This might be the least painful solution !

109

Self Assessment Questions 1) Use the array command to assist in drawing the spring in fig. Q1.1

Figure Q1.1

Figure Q1.2

110

Hints:- • Draw the three horizontal centre lines, and one vertical centre line to provide an

intersection that will be the centre of the left hand open loop. • Draw a circle to represent the OD of the left hand end open loop, then draw a line at

100° tangential to the top right quadrant of the circle to represent the start of the end loop. Set the angle to 100° in the Place Line window and use the Tangent snap to obtain the tangential contact with the circle. Finally extend the line to intersect the lower horizontal centre line.

• Use Copy Parallel to generate the wire thickness and wire centre line. • Draw a second smaller circle to represent the wire diameter taking the centre as the

intersection of the wire centreline and the outer horizontal centre line. • Draw the centreline of the slope of the first coil from the wire circle centre at 80° • Copy parallel the sides of the first coil. • Draw the wire diameter at the top of the coil. • Complete the first coil by extending and trimming lines and circles, you will need to

zoom in close to see what you are doing. • Use rectangular array to copy the coil. • Complete the end loop and then draw the construction lines as shown in the figure. • Mirror the end loop about the horizontal construction line. • Mirror the copy about the vertical construction line. • Copy this latest version of the loop onto the right end of the spring, be careful to

choose a sensible datum to copy from-to. I used the intersection of the centreline of the end coil and the central centreline.

2) Apply dimensions and annotation to the shaft fig. Q2 that you drew in lesson 3. You will have to find out for yourself how to dimension an angle!!

Figure Q2

111

3) Draw the bearing in fig. Q3, show all dimensions and tolerances.

Figure Q3

112

Hints:- • Load your A3 drawing border and immediately save as something else • The text relating to the h6 fit is particularly difficult to deal with as it inevitably

involves both a lower case character, the ‘h’, and a ∅. I used font number 106 INT_ISO_EQUAL for this dimension.

• The enlarged part section was produced by copying the section, and then scaling it by a factor of two (look this up in help). It is necessary to use the Dimension Settings window to set dimension scale to 0.5 when dimensioning this enlarged view. Don’t forget to reset the dimension scale to 1 when you have finished.

• I have shown the enlarged part section hatched, you could try to find the button to do that yourself, but hatching is covered in the next lesson, and you might want to wait until then to complete the job.

• If you are as careless as I am you will no doubt have to update dimension settings, line types, and text to the currently selected values. There are exceedingly useful buttons to do these things, find them!

Summary Having completed this lesson you should be able to:- • use the array command to generate multiple copies. • dimension components • apply tolerances to dimensions Bryan Attewell 01 August 2000

113

CAD Lesson 7 - Cells, Hatching, and Printing Introduction This is the final lesson on using Microstation in two dimensions. In it we will be finding out how to copy sections of drawings or complete components between drawings. This is a particularly useful technique, as it allows us to copy images of standard components, like nuts and bolts, between drawings and so save a good deal of time. Another drawing essential is the ability to be able to represent sectional views. The drawing standard stipulates that such views be shown cross hatched, we will be doing just that in this lesson. So far we have not determined how to obtain a print or plot using Microstation. The final part of the lesson addresses the printing problem. Aims At the end of this lesson you should be able to:- • create and copy components between drawings • draw sections with hatched areas • print or plot your drawings Using Cells In Microstation A CELL is the term used to describe a collection of elements that can be saved as a single unit and subsequently inserted into any other drawing. Cells are very useful to store standard components, e.g. electrical symbols, fasteners, welding symbols etc. These types of components typically fall into readily identifiable families, and Microstation acknowledges this by providing CELL LIBRARIES into which similar components can be placed. To use cells within Microstation it is necessary to first associate or connect a relevant cell library with the current drawing. If we intend to design our own cells, then we must open a library to keep them in. Once a cell library has been associated with a drawing it is a simple matter to extract any cell within it and place it on the current drawing. It is possible to scale the cell before placing it. This means that standard symbols can be readily adjusted to fit any size of drawing, e.g. if a drawing of a standard M10 nut is saved as a cell, then a reasonable, although not exact, drawing of an M20 nut can be obtained by scaling the M10 cell by a factor of 2. A cell may also be rotated by a specified angle before being placed on the drawing. To aid matters Microstation provides a graphical representation of the contents of a cell library, so that it is not necessary to remember the names of the individual cells when it comes to using them.

114

Each cell has a placement origin associated with it, typically at the mid point of one side, or possibly at the centre of the cell. You choose the most convenient origin for the cells that you design. A key feature of a cell is that, although it was probably defined as a set of separate elements, it exists as a single entity. So, once placed on a drawing, a cell is treated as a single element. Thus it can be easily manipulated, by moving, copying, scaling, rotating etc. It is possible to break down a cell into its component parts, but more on that later. Steps in creating a cell 1. Either attach an existing cell library to the drawing, or create a new cell library. 2. Draw the component which will form the cell 3. Draw a fence around the component 4. Indicate where the cell origin is to be 5. Save the cell within the cell library, giving it a name. The cell is then ready to use. Steps in using an existing cell 1. Attach the appropriate cell library to the drawing 2. Select the required cell 3. Specify the scaling, if required 4. Specify the angular rotation, if required 5. Insert the cell (or multiple copies of the cell) into the drawing 6. Once on the drawing the cell can be treated as a single element Creating a new cell - The M10 nut We will now draw three views of an M10 nut, and store the three views as three separate cells. The cells will be saved in a new cell library that we will create. Get into Microstation and open your standard drawing file DES1. Save it immediately as something else, I suggest the filename TRYCELL. Before we can store a new cell we must have a cell library to store it in. If an appropriate cell library already existed we could use that, but we will assume that there is no such library. We must therefore create a new cell library. Choose Element, Cells, File, New, when the Create Cell Library window should appear, fig. 1. Type in a suitable filename. I have chosen mfast, to represent Metric Fasteners. Select OK. The Cell Library window will now appear, telling us that we

115

are attached to the mfast.cel library. We can close this window for now, but we will be returning to it later.

Figure 1

Now for the M10 nut. The book supplied with the module “Manual of engineering drawing” contains a chapter on Nuts, bolts, screws and washers (Chapter 16). In there you will find precise dimensions for most common metric fasteners. We will be using the approximate construction for nuts and bolts, Figs. 16.1 and 16.2 however. The approximate construction is fine for most applications, only where space is very tight do we need to refer to the precise sizes. I have chosen the size M10 because it is then relatively easy to scale the resulting drawing to obtain other sizes, e.g. M8 is 0.8 x M10, M16 is 1.6 x M10 etc. Draw the three views of the nut using the dimensions given in fig. 16.2 of the text book, i.e. it is based upon a hexagon that has an across the corners dimension of 2D, or 20 mm. The thickness of the nut is 0.8D, i.e. 8 mm, while the radius of the central top chamfer is D, or 10 mm. My drawing of the nut, complete with all construction lines, is shown in fig. 2.

116

Figure 2

It is unnecessary to include the construction lines when saving the three views of the nut as cells. To switch the construction lines off first use Settings, Level, Display to obtain the View Levels window, then select construction lines and pick the Off button. (Note that a speedy way to get to the View Levels window is to press the CTRL and E keys simultaneously). Get rid of the window either by dragging it out of the way, or shutting it down. Now to define our cells, first the plan view. Draw a fence around the plan view of the nut, and then use the Define Cell Origin button fig. 3 to select the centre of the nut as the cell origin fig 4. A small O appears adjacent to the centre.

Figure 3.

117

Figure 4

Now use Element, Cells, Create and enter the cell name. I used M10NP to refer to the Plan view of an M10 Nut. Repeat the process for the front and side views, use the mid point of the base as the origin in these cases. I named the cells M10NF and M10NS.

Using the New Cells Having created our cells it is now time to try them out. Open the file des1 and immediately save it as trycel2. The first thing to do is to attach the relevant cell library to the present drawing. This is achieved by using Element, Cells, File, Attach, and

118

selecting the library that we previously defined, i.e. mfast.cel. The Cell Library window can be shut, or dragged out of the way now. Having attached the cell library mfast.cel to the drawing we can now use it. Select Utilities, Cell Selector, when the Cell Selector window will appear (fig. 5). The size of this window automatically adjusts to accommodate the number of cells available.

Figure 5 It is useful to leave this window open when working with cells so that any one of them can be selected easily. A Cell is selected by a single click onto the relevant miniature drawing in the cell selector window. The Place Active Cell window then appears, fig. 6.

Figure 6 The Active Angle box allows the cell to be rotated before being positioned, while the X and Y scale boxes enable you to choose the degree of magnification required. Try placing the three cells at different scales and rotations around your drawing. The other cell selection and positioning tools are shown in fig 7 below.

119

Figure 7

Starting from the left, the seven different tools are as follows:- 1. Place active cell - also controls scaling and rotation. 2. Place active cell matrix (rows and columns) - use 1 above to control scaling and

rotation before using this button. 3. Select and place cell - identify an existing cell in the design and copy it elsewhere 4. Define cell origin - covered previously. 5. Identify cell - displays a cell’s name and level 6. Place active line terminator - does not concern us at this stage ! 7. Replace cell - with another cell of the same name from the same cell library The most impressive of these commands is Place active cell matrix. Try it now, draw 20 nuts in four rows and five columns. Scale the nuts to be drawn 0.25 size, and draw them 10 mm apart. Witness the power of CAD !! The final thing to know about cells is that it is possible to break them down into their component elements. This is necessary in at least two situations:- 1. It may be necessary to partially delete a cell, perhaps our nut is partially obscured by

another component, and we need to erase only part of it. The trim command will not work with a cell, only with individual elements.

2. The cell is very similar to the part that we require, but not exactly the same. If we can break it down into its elements we can then edit them to give us the precise configuration required. This can be much faster then drawing the part from scratch.

Place a cell and then zoom in around it. Draw a line through the middle of the cell. Try to trim the cell to the line. It doesn’t work. This explosion of the cell into its component parts is achieved using the Drop Element tool shown in fig. 8.

Figure 8 Select the cell with the drop element tool and now try to trim the elements of the cell to the line that you have drawn through it. It will work this time, indeed every element can now be modified at will.

120

Sections and Hatching Many components, particularly castings and injection mouldings, have complex internal features that are not visible from the outside. They can be depicted using hidden lines, but it is usually far clearer to draw a section or sections through the component to show how the geometry varies internally. We have briefly covered sections in the earlier lesson on drawing, Chapter 8 in the text book is devoted to this subject, while there are numerous examples of sections throughout that book. I will therefore assume that you understand how to use sections, and will concentrate on those CAD specific details that you need to be aware of. There are two particular skills to be learned, using hatching, and showing appropriate cutting planes along with their associated arrows and text. Let us consider a simple example. Draw the cast bearing housing shown in fig. 9.

121

Figure 9

122

There are no special tricks involved that you have not yet learned. If you managed to draw the spring in lesson 4 you can draw anything !! The technique that we want to use is that of automatically hatching the cross-section. Figure 10 shows the relevant button to press.

Figure 10

Having selected hatching you are presented with the Hatch Area window (fig. 11). The drawing standard recommends a minimum hatching spacing of 3 mm. I have selected 5 mm at an angle of 45 deg. The Method chosen is Flood. All you have to do is to select a point within the area to hatch and Microstation works out the hatch boundary. While it is doing so a little pointer gently rotates at the bottom of the screen, just to let you know that the program is working. When it identifies the hatch boundary to its satisfaction, Microstation highlights the boundary. At that stage, if you agree with the selection click the left mouse button, when the hatching will be applied.

Figure 11

Sometimes Microstation is not clever enough to find the correct boundary, in that case click the right mouse button, and try a point in a different place. On other occasions the program cannot detect the boundary and continues to look indefinitely. If you think that this has happened then a right click should bring it to its senses, and you can try again at a different spot. If you have not provided a perfect boundary, due perhaps to idleness in not using the snaps or zooming in sufficiently, the hatch may escape all over your drawing ! Don’t panic, use the undo arrow at the top of the screen. Fix the fault in your drawing, and try again.

You will be aware by now that the drawing standard requires that different components, when sectioned together, need to have different hatch patterns. I have hatched the bearing in fig. 9 at minus 45 degrees, while the housing is hatched at 45. The second requirement of sectioning is that we mark the cutting plane using a chain dotted line which is locally thickened at any changes of direction and at the positions at which the

123

directional arrows touch it. Our centre line is appropriate for the cutting plane, locally thickened to the same weight and style as the main drawing line. If you are printing or plotting in monochrome, the easiest way to do this is to use the main drawing line on level one. If you have the luxury of colour, you should use Settings, Level, Symbology to change either the colour of the main drawing line, or the weight and style of your centre lines. Don’t forget to restore the settings when you have done. The arrow and alphabetic character indicating the particular section to be used are drawn using the Place Note tool, as introduced in the last lesson and shown in fig. 12. The appropriate letter is entered into the Text Editor window, fig. 13. It is useful to have the Axis lock when using the place note tool for this to ensure that the lines are drawn parallel to the horizontal or vertical axis. Don’t forget to switch it off when you have finished or the line drawing commands will appear to act very strangely.

Figure 12

Figure 13

Finish your drawing off by inserting your A3 drawing border cell as discussed earlier in this lesson. You may need to scale the border to get a good fit. Erasing Hatching Before we leave hatching it is appropriate to consider how we can get rid of it. The easiest way is to use the undo arrow at the top of the screen, but that is only possible if the hatch was the last command to be executed. You will find that the conventional erase command does not appear to work with hatching. The secret is to select the hatch border, rather than the hatch itself. There is a problem with this in that the hatch border is also a part of the drawing that you probably want to keep !

124

Fortunately Microstation is able to distinguish between the hatch border and your drawing outline. It will highlight the bit that it intends to erase. The hatch border is the total extent of the lines surrounding that piece of hatching, while the drawing outline will only be the particular line that you probably want to keep. Press the right mouse button to reject the erase, or the left to accept. Printing and Plotting First a brief note about the alternatives. There are at least four different types of output device that will give acceptable results when printing or plotting. They are, in order of increasing cost:- • Inkjet printer • Laser printer • Pen plotter • Ink jet plotter Virtually all professional work is done on large plotters, they may be flat bed machines, or more usually print on a roller which is fed either by single sheets of paper, or a roll of paper. In recent years ink jet plotters have taken over from pen plotters. Large plotters cost several thousand pounds to buy. If you can get access to a plotter at your place of work then you will have few problems in obtaining hard copies of your drawings. If you are working at home then you will have to make do with what you have available. I use an ink jet printer made by Epson, it cost around £200 and produces excellent plots but is limited to a maximum size of A4. Select File, Print/Plot when the Plot Window (fig. 14) appears. Note that the particular printer your system is configured to use will appear along the top of the window. In this case a HP Laser Jet 4050. You should select the orientation of the paper, Landscape or Portrait and it may be necessary to synchronise the plot to the view.

125

Figure 14 If you want to incorporate your drawings within a document you have the choice between a bitmap image, and a vector type of display. Bit maps are best for photographs or hand drawings where there are many colours and gradations of tone. Vector files are better for engineering drawings because it is possible to scale them without any loss of accuracy. For use with Microsoft Word and Microstation, the best type of vector based file is called an Hewlett Packard Graphics Language (HPGL) file, which is a file intended to be sent to a HP plotter. Some word processing programmes will accept HPGL files, but others will not. Another, more readily available, format is an Enhanced Meta File of EMF. In use you plot the EMF file to a disc and then insert it as a picture into your Word document. If you want to use a plotter at work then select the named device when Microstation will plot to a file. You can then take the file to your plotter and send it along using the DOS print command.

126

Self Assessment Question A large company involved in the telecommunications industry has decided to sub-contract the design and manufacture of a new digital telephone. Your company has decided to bid for the design of the handset, which will be injection moulded from ABS. The detail drawing of the top section of the handset is shown below, reproduce it using Microstation.

Hints 1. The centre of the large radius is a long way from the detail of the drawing. Use the centre

snap to locate this centre without showing it on the screen. 2. The hole that penetrates the top section is intended to hold a LED. Try the various

dimension options (view, drawing etc) to get this one right. It will cost a lot to buy the tooling to produce this feature, as the part will not withdraw from the mould without first retracting the part of the tool that forms it !

3. You might find it useful to open a second window when drawing the various views. This is particularly useful when you want to accurately snap on to two widely separated points, show one in each window.

4. Use your A3 drawing border cell to finish the job neatly. Summary Having completed this lesson you should be able to:- • create and copy components between drawings using cells and cell libraries • indicate section planes and draw sections with hatched areas • print or plot your drawings Bryan Attewell 19/09/2003

127

128

Past Paper EAT100 Design, Drawing and Practical Skills CAD TCA 2003-2004 – Diesel Engine Piston Time allowed 3 hours. This is an open book TCT, you may bring notes, books, and other reference materials, including computer discs, into the TCA. This assessment counts for 25% of the module mark. The attached images are taken from a solid model of a machined aluminium alloy casting of a diesel engine piston. Make a manufacturing drawing, using orthographic projection, of the part. Adopt either 1st or 3rd angle projection, and show the following views: -

1. A side elevation of the piston looking directly onto the gudgeon pin bore. 2. A plan view. 3. A view from below. 4. A sectional view taken through the vertical plane passing through the axis of the

gudgeon pin bore. Ensure that the cutting plane for the section is annotated in correspondence with the drawing standards, while the section is hatched where appropriate. All dimensions are in mm. Enclose your finished drawing within a standard drawing border showing, at minimum, the following: - 1. The correct projection symbol 2. The drawing title "Piston" 3. Your name 4. The material (Aluminium Alloy BS EN 1706: 1998 EN AC 45100) 5. A realistic overall tolerance for the machined dimensions 6. Specify, using the standard method, the more closely toleranced fit as applied to the

gudgeon pin bore, i.e. which is an H7 fit. 7. Show all dimensions, using a limited number of realistic datums. Please note that

the datums used on the sketches are not necessarily appropriate and that centre lines are often a good choice.

8. Ensure that you adopt a reasonable text size, so that dimensions and other text can be read.

It is strongly recommended that you draw a pencil sketch of your proposed layout before starting work in order to ensure that you are drawing the correct views. Further, be sure to work using the hard drive of the computer rather than a floppy disc. You

129

should copy your drawing border to the "work" directory of the C drive before starting to draw.

**DO NOT STORE YOUR WORK ON A FLOPPY DISC** Should the software lock or start to lose functionality, close down Microstation and restart the CAD program. This cures most known bugs.

130

Marking Scheme Section 20 (Including all annotation and hatching) Front view 15 (5 if incorrect projection) Top view 15 (5 if incorrect projection) Bottom view 15 (5 if incorrect projection) Toleranced fit properly specified 5 Sensible overall tolerance specified 5 Full set of dimensions 10 Material specified 5 Drawing contained in an appropriate border with projection symbol 10 Bryan Attewell 20/10/2003

131

132

133

134

135