technical sketching c h a p t e r t h r e e. technical drawing with engineering graphics, 14/e...

TECHNICALTECHNICALSKETCHINGSKETCHING

C H A P T E R T H R E E

Technical Drawing with Engineering Graphics, 14/eGiesecke, Hill, Spencer, Dygdon, Novak, Lockhart, Goodman

© 2012, 2009, 2003, Pearson Higher Education,Upper Saddle River, NJ 07458. • All Rights Reserved.

OBJECTIVESOBJECTIVES

After studying the material in this chapter, you should be able to:

1. Define the terms vertex, edge, plane, surface, and solid.

2. Identify four types of surfaces.

3. Identify five regular solids.

4. Draw points, lines, angled lines, arcs, circles, and ellipses.

5. Apply techniques that aid in creating legible well-proportioned freehand sketches.

6. Apply techniques to draw irregular curves.

7. Create a single-view sketch.

8. Create an oblique sketch.

9. Create perspective sketches.

10. Create an isometric sketch of an object.

Shaded Sketch Showing Details of Wire Placement. (Courtesy of Quantum Design.)



UNDERSTANDING SOLID UNDERSTANDING SOLID OBJECTSOBJECTS

Three-dimensional figures are referredto as solids. Solids are bounded bythe surfaces that contain them. Thesesurfaces can be one of the following fourtypes:

• Planar• Single curved• Double curved• Warped

Regardless of how complex a solid may be, it is composed of combinations of these basic types of surfaces.



UNDERSTANDING SKETCHINGUNDERSTANDING SKETCHINGTECHNIQUESTECHNIQUES

break down complex shapes into simpler geometricprimitives

Look for the essential shapes of objectsAnd use construction lines



SKETCHINGSKETCHINGTECHNIQUESTECHNIQUES

The contours of an object are the main outlines that separate it from the surrounding space. One way to think about the contours of objects is to look at the contrast between the positive and negative space. Positive space is the space occupied by the object. Negative space is the unoccupied space around it.



VIEWPOINT AND SHADINGVIEWPOINT AND SHADING

As you sketch objects, keep in mind that you want to maintain a consistent viewpoint, like a camera does.

Adding shading to your sketch can give it a more realistic appearance because it represents the way the actual object would reflectlight.

Hatching and stippling



EDGES AND VERTICESEDGES AND VERTICES

EdgesAn edge of the solid is formed where two surfaces intersect. Edges are represented in drawings by visible or hidden lines.

VerticesA vertex (plural, vertices) of a solid is formed where three or more surfaces intersect..

Points and LinesA point is used to represent a location in space but has no width, height, or depth.



POINTS AND LINESPOINTS AND LINESA point is used to represent a location in space but has no width, height, or depth.

A line is used in drawings to represent the edge of a solidobject.



ANGLESANGLESAn angle is formed by two intersecting lines. A common symbol for angle is .

Showing Angles



DRAWINGS AND SKETCHESDRAWINGS AND SKETCHESThe following are important skills to keep in mind for sketchesand drawings:

1.Accuracy. No drawing is useful unless it shows the information correctly.

2. Speed. Time is money in industry. Work smarter and learn to use techniques to speed up your sketching and CAD drawings while still producing neat accurate results.

3. Legibility. A drawing is a means of communicating with others, so it must be clear and legible. Give attention to details. Things that may seem picky and small as you are drawing may be significant and save money or even lives when the product is built.

4. Neatness. If a drawing is to be accurate and legible, it must also be clean.



FREEHAND SKETCHINGFREEHAND SKETCHINGFreehand sketches are a helpful way to organize your thoughts and record ideas. They provide a quick, low-cost way to explore various solutions to design problems so that the best choices canbe made.



TECHNIQUE OF LINESTECHNIQUE OF LINESThe chief difference between a drawing and a freehand sketch lies in the character or technique of the lines.

line patterns

A good freehand line is not expected to be as rigidly straight or exactly uniform. A good freehand line shows freedom and variety, whereas a line drawn using CAD or instruments should be exact.



GOOD AND POOR TECHNIQUEGOOD AND POOR TECHNIQUE



LINEWEIGHTSLINEWEIGHTSEven in freehand drawings, thick lines should be twice the width of thin lines.Thicknesses do not have to be exact, but there should be an obvious difference between thick and thin lines. Because visible lines and cutting-plane lines are the two thick line patterns, other lines should be distinctlythinner in comparison.

To draw thick and thin lines freehand,you might like to keep two pencilshandy, one that is razor sharp for thinlines and another that is dulled, tocreate thicker lines. As the sharp pointbecomes dulled, switch it with thedull pencil, and sharpen the other,so that there is always one sharpand one dulled point ready to use.



SKETCHING STRAIGHT LINESSKETCHING STRAIGHT LINESMost of the lines in an average sketch are straight lines. Withpractice, your straight lines will naturally improve, but thesebasics may help you improve quickly.

• Hold your pencil naturally, about 1" back from the point, and approximately at a right angle to the line to be drawn.

• Draw horizontal lines from left to right with a free and easy wrist and arm movement.

• Draw vertical lines downward with finger and wrist movements.



STRAIGHT LINE TIPSSTRAIGHT LINE TIPS



STRAIGHT LINE TIPS STRAIGHT LINE TIPS CONTINUED…CONTINUED…



METHODS FORMETHODS FORSKETCHING CIRCLESSKETCHING CIRCLES



METHODS FOR SKETCHING METHODS FOR SKETCHING ARCSARCS



METHODS FOR SKETCHING METHODS FOR SKETCHING ELLIPSESELLIPSES



MAINTAINING PROPORTIONSMAINTAINING PROPORTIONSThe most important rule in freehand sketching is to keep the sketch inproportion, which means to accurately represent the size and position of each part in relation to the whole.

To maintain proportions, first determine the relative proportions of height to width and lightly block them in. You can mark a unit on the edge of a strip of paper or use your pencil to gauge how many units wide and high the object is.



ONE-VIEW DRAWINGSONE-VIEW DRAWINGSFrequently, a single view supplemented by notes and dimensionsis enough information to describe the shape of a relativelysimple object.

Note how thickness of the material is given as “0.25 BRASS” So, an additional view is not needed to dimensionally give the material thickness.



PICTORIAL SKETCHINGPICTORIAL SKETCHINGA pictorial sketch represents a 3D object on a 2D sheet of paperby orienting the object so you can see its width, height, and depth in a single view.



AXONOMETRICAXONOMETRICDRAWINGSDRAWINGS

Various types of pictorial drawings are used extensively in catalogs,sales literature, and technical work. They are often used in patent drawings; in piping diagrams; in machine, structural, architectural design, and in furniture design; and for ideation sketching.

Axonometric

(Courtesy of Douglas Wintin.)



PROJECTION PROJECTION METHODSMETHODS

The four principal types of projections:

a Multiview b Axonometric c Oblique d Perspective



ISOMETRIC DRAWINGS STEPS…



OBLIQUE SKETCHING STEPS…OBLIQUE SKETCHING STEPS…



PERSPECTIVE DRAWING PERSPECTIVE DRAWING ONE-ONE-POINTPOINT STEPS… STEPS…



PERSPECTIVE DRAWING PERSPECTIVE DRAWING TWO-TWO-POINTPOINT STEPS… STEPS…



SHADINGSHADINGShading can make it easier to visualize pictorial drawings, such as display drawings, patent drawings, and catalog drawings.

Methods of Shading

Ordinary multiview and assembly drawings are not shaded.

C H A P T E R F O U RGEOMETRICGEOMETRIC

CONSTRUCTIONCONSTRUCTION



OBJECTIVESOBJECTIVES

1. Identify the geometry that makes up basic 2D drawings.

2. Use board drafting or 2D CAD skills to create technical figures.

3. Describe the advantages of CAD contrasted with drawing with manual instruments



GEOMETRY REVIEWGEOMETRY REVIEW

• Triangles

• Quadrilaterals

• Polygons

• Circles

• Arcs



BISECTING A LINE BISECTING A LINE OR CIRCULAR ARCOR CIRCULAR ARC

Triangle and T-Square System Compass system



BISECTING A LINE WITH TRIANGLE

AND T-SQUAREFrom endpoints A and B, draw construction lines at 30°, 45°, or 60° with the given line. Then, through their intersection, C, draw a line perpendicular to the given line to locate the center D…



TRIANGLESTRIANGLESInclined lines can be drawn at standard angles with the 45° triangle and the 30° x 60° triangle. The triangles are transparent so that you can see the lines of the drawing through them. A useful combination of triangles is the 30° x 60° triangle with a long side of 10" and a 45° triangle with each side 8" long.



ANY ANGLE IN 15° INCREMENTSANY ANGLE IN 15° INCREMENTS

With only a 30° x 60° triangle and a 45° triangle, you can drawany angle in 15° increments

The bottomof the triangle ineach case is resting on the blade of theT-square. Twenty-four 15° sectors are possible with just these two triangles used singly or in combination.



PROTRACTORSPROTRACTORSFor measuring or setting off angles other than those obtainable with triangles, use a protractor.

Plastic protractors are satisfactory for most angular measurements

Nickel silver protractors are available when high accuracyis required



ANGLES…ANGLES…

BISECTING AN ANGLE

TRANSFERRING AN ANGLE



DRAWING A LINE PARALLEL TO DRAWING A LINE PARALLEL TO A LINE AND AT A GIVEN A LINE AND AT A GIVEN

DISTANCEDISTANCE

For CurvesT-square Method



DRAWING A LINE THROUGH A DRAWING A LINE THROUGH A POINT AND PERPENDICULAR TO POINT AND PERPENDICULAR TO

A LINEA LINE

When the Point Is Not on the Line When the Point Is on the Line T-square Method



TRIANGLES…TRIANGLES…

DRAWING A TRIANGLE WITH SIDES GIVEN

DRAWING A RIGHT TRIANGLE WITHHYPOTENUSE AND ONE SIDE GIVEN



LAYING OUT AN ANGLELAYING OUT AN ANGLE• Tangent Method• Sine Method• Chord Method

Many angles can be laid out directly with the triangle or protractor.



DRAWING AN EQUILATERALDRAWING AN EQUILATERALTRIANGLETRIANGLE

Alternative Method



DRAWING A SQUAREDRAWING A SQUARE

You can use the AutoCAD Polygoncommand to draw squares. The Rectangle command is another quick way to make a square in AutoCAD.

• T-square Method• Diameters Method• Inscribed Circle Method



DRAWING A REGULAR DRAWING A REGULAR PENTAGONPENTAGON

Dividers Method Geometric Method



DRAWING A HEXAGONDRAWING A HEXAGONEach side of a hexagon is equal to the radius of the circumscribed circle

Use a compass Centerline Variation

Steps



DRAWING AN OCTAGONDRAWING AN OCTAGON

Given an inscribed circle, or distance “across flats”, use a T-square or straightedge and a 45° triangle to draw the eight sides tangent to the circle.

Given a circumscribed square, (the distance “across flats”) draw the diagonals of the square. Then, use the corners of the square as centers and half the diagonal as the radius to draw arcs cutting the sides



FINDING THE CENTER OF A FINDING THE CENTER OF A CIRCLECIRCLE

This method uses the principle that any right triangle inscribed in a circle cuts off a semicircle.

Another method, slightly longer, is to reverse the procedure. Draw two nonparallel chords and draw perpendicular bisectors. The intersection of the bisectors will be the center of the circle.



DRAWING TANGENTS TO TWO DRAWING TANGENTS TO TWO CIRCLESCIRCLES

AutoCAD software provides a convenient object snap for finding tangency.



DRAWING AN ARC TANGENT TO DRAWING AN ARC TANGENT TO A LINE OR ARC A LINE OR ARC

AND THROUGH A POINTAND THROUGH A POINT

TangentsTangents



DRAWING AN ARC TANGENT TO DRAWING AN ARC TANGENT TO TWO LINES AT RIGHT ANGLESTWO LINES AT RIGHT ANGLES

For small radii, such as 1/8R for fillets and rounds, it is not practicable to draw complete tangency constructions. Instead, draw a 45° bisector of the angle and locate the center of the arc by trial along this line



DRAWING AN ARC TANGENT TO DRAWING AN ARC TANGENT TO TWO LINES AT ACUTE ORTWO LINES AT ACUTE OR

OBTUSE ANGLESOBTUSE ANGLES



DRAWING AN ARC TANGENT TO DRAWING AN ARC TANGENT TO AN ARC AND A STRAIGHT LINEAN ARC AND A STRAIGHT LINE



DRAWING AN ARC TANGENT TO DRAWING AN ARC TANGENT TO TWO ARCSTWO ARCS



DRAWING AN ARC TANGENT TO DRAWING AN ARC TANGENT TO TWO ARCS AND ENCLOSING TWO ARCS AND ENCLOSING

ONE OR BOTHONE OR BOTH



DRAWING AN OGEE CURVEDRAWING AN OGEE CURVE

Connecting Two Parallel Lines Connecting Two Nonparallel Lines



THE CONIC SECTIONSTHE CONIC SECTIONS

The conic sections are curves produced by planes intersecting a right circular cone.

Four types of curves are produced: the circle, ellipse, parabola, and hyperbola, according to the position of the planes.



DRAWING A FOCI ELLIPSEDRAWING A FOCI ELLIPSE



DRAWING A CONCENTRIC DRAWING A CONCENTRIC CIRCLE ELLIPSECIRCLE ELLIPSE

If a circle is viewed with the line of sight perpendicular to the planeof the circle…

…the circle will appear as a circle, in true size and shape



DRAWING A PARALLELOGRAM DRAWING A PARALLELOGRAM ELLIPSEELLIPSE

The intersection of like-numbered lines will be points on the ellipse. Locate points in the remaining three quadrants in a similar manner. Sketch the ellipse lightly through the points, then darken the final ellipse with the aid of an irregular curve.



ELLIPSE TEMPLATESELLIPSE TEMPLATESThese ellipse guides are usually designated by the ellipse angle, the angle at which a circle is viewed to appear as an ellipse.



IRREGULAR CURVESIRREGULAR CURVESThe curves are largely successive segments of geometric curves, such as the ellipse, parabola, hyperbola, and involute.



DRAWING AN APPROXIMATE DRAWING AN APPROXIMATE ELLIPSEELLIPSE

For many purposes, particularly where a small ellipse is required, use the approximate circular arc method.



DRAWING A PARABOLADRAWING A PARABOLAThe curve of intersection between a right circular cone and a plane parallel to one of its elements is a parabola.



DRAWING A HELIXDRAWING A HELIXA helix is generated by a point moving around and along the surface of a cylinder or cone with a uniform angular velocity about the axis, and with a uniform linear velocity about the axis, and with a uniform velocity in the direction of the axis



DRAWING AN INVOLUTEDRAWING AN INVOLUTEAn involute is the path of a point on a string as the string unwinds from a line, polygon, or circle.



DRAWING A CYCLOIDDRAWING A CYCLOIDA cycloid is generated by a point P on the circumference of a circle that rolls along a straight line

Cycloid



DRAWING AN EPICYCLOID OR A DRAWING AN EPICYCLOID OR A HYPOCYCLOIDHYPOCYCLOID

Like cycloids, these curves are used to form the outlines of certain gear teeth and are thereforeof practical importance in machine design.

technical sketching c h a p t e r t h r e e. technical drawing with engineering graphics, 14/e...

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