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Activity 8.2 Parametric ConstraintsIntroduction

Have you ever received an advertisement in the mail that looked like it was tailored specifically for you? How could the company afford to spend so much time and money entering your name and other personal information into the various locations of the advertisement? In order to create such advertisements, the company will store your personal information within a database. A computer will then plug specific pieces of your personal information into various locations on a generic document with links to the database. The same thing happens with email advertisements. This type of work takes a great deal of preplanning to pull off, but the efforts are worth it if a number of customers respond.

Engineers perform similar types of plug and produce operations, specifically in the area of 3D CAD solid modeling. Numeric constraints, also referred to as parametric dimensions, may not always have a fixed number value. Some objects must be customized, like a tailored suit or dress. If you were to return to one of your elementary school classrooms, you would think that someone took normal-sized furniture and uniformly scaled it down. That could very well have been the case. If designed correctly in a 3D CAD solid modeling program, the furniture that you interact with as a young adult can be scaled down by changing one or more dimensions. Companies are beginning to build this type of design flexibility into their internet-based customer ordering systems. If the customer enters specific dimensional values, colors, and sometimes materials into the online database, the computer updates the sizes and features of the various associated parts, and then places and delivers an order to the company staff. This is only one example of the power of parametric modeling.

In this activity you will learn how algebraic formulas can be used to replace numeric values in a 3D CAD solid model.

Equipment Computer with 3D CAD solid modeling software Engineering notebook Number 2 pencil

© 2012 Project Lead The Way, Inc. IED Activity 8.2 Parametric Constraints –

Procedure

1. Study the image below and table on the next page. Complete the following tasks.


Dimension Description Geometric Relationship

Parametric Equation Value

d0 Overall Plate Depth -- -- 3 in.

d1 Overall Plate Width

5:3 ratio; overall plate

width to overall plate depth

d0*(5/3)

d2 Plate Thickness

20 times smaller than the overall

width

d1/20

d3 Plate Taper Angle

perpendicular to the top and bottom plate

surfaces

-- 0°

d4 Slot Width ½ the overall plate depth d0/2

d5 Slot Width Location

4/5 of the overall plate

width

d6 Slot Depth Location


depth

d7 Slot Radius same as the plate thickness d2

d8 Slot Extruded Height

same as the plate thickness

d9 Slot Taper Angle

same as the plate taper

angled3

d10 Hole Width Location

¼ of the overall plate width

d11 Hole Depth Location


depth

d12 Hole Diameter twice the slot radius 2*d7

d13 Hole Extruded Height

same as the slot height

d14 Small Hole Taper Angle

same as the slot taper angle d9

a. Use the given information to fill in the missing parametric equations and missing numeric values for each parameter in the table below.


b. Use your parametric equations to create the object above in a 3D CAD solid modeling program. Be sure to use the same parameter names for each dimension as identified in the table in number 1. The only numeric values that you should enter are 3 inches for dimension d0, and 0° for dimension d3. All other parameters should be defined using a formula. When finished, save the file and identify its name and location in your student folder. NOTE: The hole (diameter d12) was created using the CIRCLE tool.

File name: ______________________ Location: _________________________

1. Sketch a rectangle. Dimension the depth first (d0) and then the width (d1).

2. Extrude the rectangle the appropriate distance (d2) using a formula. Note that a parameter will automatically be assigned for the taper angle (d3) of the extrusion. The default taper angle is zer0 degrees.

3. Sketch and dimension the slot on the top surface of the plate using the parameter names shown and the appropriate formulas. Be sure that the semicircular ends of the slot are tangent to the straight edges of the slot.

4. Extrude Cut the slot the appropriate distance (d8). Again, a parameter will automatically be assigned for the taper angle of the extrusion (d9).


5. Sketch and dimension a circle on the top surface of the plate to represent the hole using the parameter names shown and appropriate formulas.

6. Extrude Cut the hole the appropriate distance (d14). Again, a parameter will automatically be assigned for the taper angle (d13).

c. Record the physical properties of the part below.

Volume: _________________ Surface Area: __________________

d. Change the overall plate depth to 1.5 inches, that is d0 = 1.5 in. Be prepared to demonstrate the change to your teacher.

i. Describe what happens to the plate and the features when you revised the dimension.

ii. Record the physical properties of the part after it is resized.

Volume: ________________ Surface Area: __________________


2. An aluminum (density 2.710 g/cm3) part is represented in the image below. This part must be created using parametric constraints so that it can be quickly and accurately resized when necessary. Complete each of the follow tasks.


a. What drawing views are displayed above? How does each view help describe the part?

b. Create the part as a 3D CAD solid model. Use the following parametric constraints to dimension the model.

The overall height of the part is 2 inches

The top width is 0.5 inches

The right height is ¼ inch less than half of the overall height

The overall width is 50 percent larger than the overall height

The depth is 0.25 inches greater than the overall height

The upper hole diameter is 1/8 in. larger than the top width


The lower hole diameter is 1/16 in. less than the upper hole diameter

The edge distance (the distance from the outside circumference of the hole to the edge of the part) from the lower hole to the right edge of the part (along the inclined plane) is 1/8 in. greater than one quarter of the upper hole diameter (see drawing). Note that you will dimension to the hole center in the model but are given a constraint on the edge distance. Call the distance from the lower hole center to the right edge right to hole center distance in the parameter table.

The hole centers are aligned at the same distance from the back edge of the included plane. The hole center-to-center distance is 1/8 in. less than half of the overall width.

The distance from the back edge to the hole centers is one third of the part depth.

The hole depth of both holes is half the diameter of the lower hole

The notch width is 35 percent of the overall width

The notch depth is always 0.25 inches.

The notch is centered in the front face from left to right. The notch location is the distance from the right face to the right edge of the notch (see drawing).

The inside vertical edges of the notch are filleted to a fillet radius of ¼ the top width.

The shell thickness is half of the hole depth.

c. Edit the parameter table for your part in the 3D CAD solid modeling software in order to identify each dimension that is underlined in the constraints list. That is, either rename a parameter to match each underlined label (Example 1, below) or add each underlined dimension label in the comment column in the appropriate row (Example 2, below).

Example 1:

Example 2:


d. Find the following physical properties of the part as described above.

Overall Width: _____________Right to Hole Center: ______________Hole Center-to-Center: __________________Volume: _________________Surface Area: ___________________Mass: __________________

e. Change the overall width of the part to 3.5 inches and the top width to 3/8 in. Be prepared to demonstrate the change in the part within the software for your teacher. Find the following physical properties of the resized part.

Overall Width: ____________________Right to Hole Center: __________________Hole Center-to-Center: ___________________Volume: __________________Surface Area: _________________Mass: _______________________

f. What view would be helpful in order to show and properly dimension the shell thickness?

3. (Optional) An image of an Automoblox T9 vehicle (full size) and an image of an Automoblox T9 Mini vehicle are shown below. Each image includes a ruler. A multi-view drawing of a simplified Passenger Base for the full sized vehicle is also provided. Assuming that the Mini vehicle is simply a scaled down version of the full sized toy, create a CAD part file for the T9 that will allow the user to create a part model of the Passenger Base for the Mini by simply changing the overall width of the part. Note that the edge round radius (0.02 inches) is a function of the equipment used to create the parts and will remain the same for both vehicles. Also note that the holes for the connector inserts are identical on opposite faces and that all holes (for the passengers and for the connector inserts) are assumed to be centered on the part faces.


Automoblox T9 Automoblox T9 Mini

a. Create a part file for the full size T9 Passenger Base part. You may want to make annotations in the comment column of the parameter table as you create the part to document your dimensioning. Record the following physical properties of the full-size Passenger Base. Note: Be sure to create a new part file for the Passenger Base according to the given dimensions. For the purposes of this exercise, do not use a previously created part file.

Volume: ____________________

Surface Area: __________________

Mass: _________________


b. Revise your 3D solid modeling parameter table for the Passenger Base to include parametric equations specifying the relationship among parameters in order to allow a scaled resizing of the part.

c. By what factor should you multiply the overall width of the full-size part in order to obtain the overall width of the Mini? Hint: Use approximate measurements (see images) to approximate the relationship.

Full sized dimension x __________ = Mini dimension

d. If all of the parametric equations are written correctly, the object should increase or decrease in size and maintain its geometric proportions. Test your part file by scaling the object down to produce a T9 Mini Passenger Base. Record the following physical properties for the Mini part.

Overall width: _____________________

Overall height: ______________________

Volume: ____________________

Surface Area: __________________

Mass: _________________

e. (Optional). Produce a fully dimensioned part drawing for the Passenger Base for the T9 Mini.

4. (Optional) Model an object of your teacher’s choosing (Button Maker base plate, Arbor Press cover plate, or train part) in a 3D CAD solid modeling program. You will need to use geometric constraints to limit the number of parametric dimensions that are needed. Test your results by scaling the object up or down. If all of the parametric equations are written correctly, the object should increase or decrease in size and maintain its geometric proportions. When finished, save the file and identify its name and location in your student folder.

Conclusion1. What is the difference between a numeric and a geometric constraint?

2. What advantages are there to using parametric equations instead of numeric values?


3. What disadvantages are there to using parametric equations for numeric values?

4. Describe a situation in which using parametric equations to dimension an object would be helpful.


activity 8.2 parametric constraintssjolanderengineering.weebly.com/uploads/2/2/7/3/22738998/... ·...

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