Activity 5.2a Geometric Constraints
Introduction
There are several types of constraints that can be applied within a 3D solid modeling
program to control the geometry associated with a solid model: geometric
constraints, dimension constraints, and assembly constraints. We will talk about
dimension constraints and assembly constraints later in this lesson. In this activity
we will explore geometric constraints.
Geometric constraints are applied in CAD programs to control geometry within
sketches and enforce relationships between lines, arcs, circles, and other geometry.
Examples of geometric constraints include parallel, perpendicular, concentric, and
equal.
Constraints are often automatically applied by the software as you create a sketch in
a CAD program. Sometimes you don’t even realize the constraints are being
applied. For instance, to ensure that a rectangle always remains a rectangle in a
sketch, a CAD program will automatically apply constraints when you create a
rectangle using the rectangle tool.
However, you can also manually apply geometric constraints to a sketch to force the
geometry to behave in a way that you intend.
In this activity you will investigate the effect that constraints have on the behavior of
a sketch and try to replicate that behavior in a CAD sketch by applying appropriate
constraints.
Equipment
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PLTW Engineering notebook
Pencil
Computer with 3D modeling software
Procedure
1. Open a new Inventor part file in Inventor. Create a sketch and experiment with
each geometric constraint so that you become familiar with how the constraints
affect the sketch behavior. Be sure to show the applied constraints so that you
may understand how Inventor indicates the application of each constraints.
2. View each of the videos posted on the Activity 5.2a Geometric Constraints page.
In the appropriate column in the following table, draw a representation of the
Inventor sketch presented in each video in its initial form. On each sketch
indicate the geometric constraints that you think are applied to the geometry in
each case.
© 2011 Project Lead The Way, Inc.
PLTW Introduction to Engineering Design 5.2a Geometric Constraints – Page 1
3. In Inventor, create each sketch and apply the appropriate constraints to enforce
the same sketch behavior as is demonstrated in each video. Demonstrate the
behavior of each sketch to your teacher to get approval.
Video
Sketch geometry with geometric constraints
Teacher
initials
1
2
3
© 2011 Project Lead The Way, Inc.
PLTW Introduction to Engineering Design 5.2a Geometric Constraints – Page 2
4
5
© 2011 Project Lead The Way, Inc.
PLTW Introduction to Engineering Design 5.2a Geometric Constraints – Page 3
Conclusion Questions
1. Why is it important to use constraints when sketching with your 3D modeling
program?
2. Why are some constraints automatically applied by the software, but you must
manually apply others?
3. Study the shape shown below.
Original figure
Box A
Box B

Consider which geometric constraint you would apply to the triangle to
change it to a right triangle. Sketch the resulting right triangle in Box A
and show the icons for the constraint(s) as they would appear if applied in
Inventor.

Consider which geometric constraint you would apply to the right triangle
to change it to a right isosceles triangle. Sketch the resulting triangle in
Box B and show the icons for the constraint(s) as they would appear if
applied in Inventor.
© 2011 Project Lead The Way, Inc.
PLTW Introduction to Engineering Design 5.2a Geometric Constraints – Page 4