Activity 2.3.2 – Parametric Constraints
Answer Key
Purpose
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? The answer is the company took your personal information
that it has within a database, and had a computer plug specific pieces of your
personal information into various locations of a generic document that was set up
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 places
and delivers an order to the company staff. This is only one example of the power of
parametric modeling.
Equipment



Computer with 3D CAD solid modeling software
Engineer’s notebook
Number 2 pencil
Procedure
In this activity, you will learn how algebraic formulas can be used to replace numeric
values in a 3D CAD solid model.
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IED – Unit 2 – Lesson 2.3 – Activity 2.3.2 – Parametric Constraints Answer Key– Page 1
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IED – Unit 2 – Lesson 2.3 – Activity 2.3.2 – Parametric Constraints Answer Key– Page 2
Study the images on the previous pages, and table below. Use the given information
to calculate the missing values. Create the object in a 3D CAD solid modeling
program using the dimensions and parametric equations provided. The only numeric
value that you should enter is 3 inches for dimension d0. When finished, identify the
name and location of your CAD file.
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IED – Unit 2 – Lesson 2.3 – Activity 2.3.2 – Parametric Constraints Answer Key– Page 3
Dimension
Description
Geometric
Relationship
Parametric
Equation
Value
d0
Overall Plate
Depth
--
--
3 in
d1
Overall Plate
Width
d0*(5/3)
5 in
d2
Plate Thickness
d1/20
.25 in
d3
Plate Taper
Angle
--
0°
d4
Slot Width
d0/2
1.5 in
d5
Slot Width
Location
d1*.8
4 in
d6
Slot Depth
Location
d1/3
1 in
d7
Slot Diameter
d2*2
.5 in
d8
Slot Extruded
Length
d2
.25 in
d9
Slot Taper
Angle
d3
0°
d10
Hole Width
Location
d1*.25
1.25 in
d11
Hole Depth
Location
d0*.67
2 in
d12
Hole Diameter
d7
.5 in
d8
.25 in
d9
0°
d13
d14
Hole Extruded
Length
Small Hole
Taper Angle
5:3 ratio;
overall plate
width to overall
plate depth
20 times
smaller than
the overall
width
perpendicular
to the top and
bottom plate
surfaces
½ the overall
plate depth
4/5 of the
overall plate
width
1/3 of the
overall plate
depth
two times the
plate thickness
same as the
plate thickness
same as the
plate taper
angle
¼ of the overall
plate width
2/3 of the
overall plate
depth
same as the
slot diameter
same as the
slot height
Same as the
slot taper angle
CAD file name and location:
Model the Arbor Press Cover Plate in a 3D CAD solid modeling program. You will
need to use geometric constraints to limit the number of parametric dimensions that
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IED – Unit 2 – Lesson 2.3 – Activity 2.3.2 – Parametric Constraints Answer Key– Page 4
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.
Example Sketch of an Arbor Press Part
CAD file name and location:
Dimension
d3
d9
d10
Description
Plate Taper Angle
Extruded Hole Lengths
Hole Taper Angles
Taper Angles and Hole Extrusion Length Dimensions
Dimension
Description
Geometric
Relationship
Parametric
Equation
Value
d0
Plate Width
--
--
1 in
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IED – Unit 2 – Lesson 2.3 – Activity 2.3.2 – Parametric Constraints Answer Key– Page 5
d1
Plate Height
d2
Plate Depth
d3
Plate Taper
Angle
Hole 1 & 4
width location
Hole 2 & 3
width location
Hole 1 & 2
height
location
Hole 3 & 4
height
location
Diameter of
the holes
Extrusion
length of the
holes
d4
d5
d6
d7
d8
d9
Twice the
Plate Width
37% of the
Plate Width
perpendicular
to the front
plate surface
87.5% of the
Plate Width
12.5% of the
Plate Width
87.5% larger
than the Plate
Width
Identical to
Hole 2 & 3
width location
17.2% of the
Plate Width
Identical to the
Plate Depth
d0*2
2 in
d0*.37
.37 in
--
0°
d0*.875
.875 in
d0*.125
.125 in
d0*1.875
1.875 in
d5
.125 in
d0*.172
.172 in
d2
.37 in
Identical to the
Plate Taper
d3
Angle
Example Cover Plate Parametric Table
Taper angles
of the holes
d10
0°
Conclusion
1. What is the difference between a numeric and a geometric constraint?
A numeric constraint is a location or size dimension that is used on a
geometric figure, and can be identified as a numeric value or a parametric
equation. A geometric constraint is an assigned relationship that governs the
orientation of two sketched elements with respect to each other. Examples of
geometric constraints include collinear lines, concentric arcs or circles,
parallel lines, perpendicular lines, and fixed points.
2. What advantages are there to using parametric equations instead of numeric
values?
A parametric equation will maintain a constant geometric relationship between
two or more dimensional characteristics of an object. If a dimensional value
changes, the parametric equations will automatically change any associated
dimensional characteristics, thus maintaining proportionality. Parametric
dimensions in a solid CAD model can be linked to spreadsheet programs that
are capable of performing more complex mathematical operations. The
product of these operations will update the model and all of its associated
working drawings.
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IED – Unit 2 – Lesson 2.3 – Activity 2.3.2 – Parametric Constraints Answer Key– Page 6
3. What disadvantages are there to using parametric equations for numeric values?
Extensive knowledge of the geometric relationships that exist between an
object’s features must be understood and identified before the object is
generated as a CAD model. This requires a time investment that is not
required when using only numeric values. Not all objects experience the types
of changes that make the use of parametric equations an efficient alternative.
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IED – Unit 2 – Lesson 2.3 – Activity 2.3.2 – Parametric Constraints Answer Key– Page 7
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Parametric Constraints Answer Key