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8.2 Parametric Constraints
Introduction
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.
Instruction
Complete this assignment in your notebook and in Inventor. Create a new
project in Inventor titled “8.2 Parametric Constraints FirstInitial LastName.” Follow the
directions carefully and please ask if you have questions. We will work together on
Number 1 and you will demonstrate what you have learned on Number 2.
Due: Monday March 30th
Submit: Zipped project folder of Inventor files to Turnitin.com, Engineering notebook to
me.
Page 1
Procedure
1. Study the image below and table on the next page. Complete the following tasks.
Page 2
a. Use the given information to fill in the missing parametric equations and missing
numeric values for each parameter in the table below.
Dimension
Description
Geometric
Relationship
Parametric
Equation
Value
d0
Overall Plate
Depth
--
--
3 in.
d1
Overall Plate
Width
d2
Plate Thickness
d3
Plate Taper
Angle
d4
Slot Width
d5
Slot Width
Location
d6
Slot Depth
Location
d7
Slot Radius
d8
Slot Extruded
Height
d9
Slot Taper
Angle
d10
Hole Width
Location
d11
Hole Depth
Location
d12
Hole Diameter
d13
d14
Hole Extruded
Height
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
same as 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
twice the slot
radius
same as the
slot height
same as the
slot taper angle
d0*(5/3)
d1/20
--
0°
d0/2
d2
d3
2*d7
d9
Page 3
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.
NOTE: The hole (diameter d12) was created using the CIRCLE tool. Material is
Steel.
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 zero 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).
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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 in your notebook (material
Steel).
Volume: _________________
Surface Area: __________________
d. Change the overall plate depth to 1.5 inches, that is d0 = 1.5 in.
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: __________________
Page 5
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
following tasks.
Page 6
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.
DOCMENT: construct a table in your notebook, like in 1a, for the
dimensions below. This will prevent errors and help you find them.

The overall height of the part is 2 inches (d0)

The top width is 0.5 inches (d1)

The right height is ¼ inch less than half of the overall height (d2)

The overall width is 50 percent larger than the overall height (d3)

The depth is 0.25 inches greater than the overall height (d4 and d5 =
0°

The upper hole diameter is 1/8 in. larger than the top width (d6)

The lower hole diameter is 1/16 in. less than the upper hole diameter
(d7)

The edge distance (d8) 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).

The hole centers are aligned at the same distance from the back edge
of the included plane. The hole center-to-center (d9) distance is 1/8
in. less than half of the overall width.

The distance from the back edge to the hole centers (d10) is one
third of the part depth.

The hole depth (d11) 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).
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
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 Inventor 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. Find the following physical properties of the resized part.
Overall Width: ____________________
Right to Hole Center: __________________
Hole Center-to-Center: ___________________
Volume: __________________
Surface Area: _________________
Mass: _______________________
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f. What view would be helpful in order to show and properly dimension the
shell thickness?
Conclusion
1. 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.
Page 9