EGR 110 – Inventor Lecture #2
Geometric Constraints
As introduced last class, we control sketches (or express our design intent) using :
• Dimensions
• Geometric constraints
Inventor allows you to easily apply constraints, such as making features perpendicular,
parallel, tangent, etc. Many of the features will be applied automatically, but can be
turned off or changed as desired. Inventor has 11 geometric constraints that you can
apply to a sketch, as shown below from the 2D Sketch Panel
Names added
for convenience
Coincident
Parallel
Tangent
Colinear
Perpendicular
Smooth
Concentric
Horizontal
Symmetric
Fix
Vertical
Parallel
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EGR 110 – Inventor Lecture #2
Geometric Constraints
Quick explanations of each type of geometric
constraint are provided below.
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Coincident – A gap between two endpoints of arcs and/or
lines will be closed.
Collinear – Two selected lines or points will line up along
a single line. If the first line moves, so will the second. The two lines do not have to be touching.
Concentric – Arcs and/or circles will share the same center point.
Fix – Used to fix an endpoint or any other point to the permanent (world) coordinate system. This
constraint overrides all other constraints.
Perpendicular – The first line will stay in position and the second line will rotate until it forms a 90o
angle with the first line.
Horizontal – Lines are positioned parallel to the x-axis. Can also be used to specify that center points
of circles to share the same horizontal axis.
Vertical – Lines are positioned parallel to the y-axis. Can also be used to specify that center points of
circles to share the same vertical axis.
Tangent – An arc or circle and a line will become tangent to another arc or circle.
Equal – Used to specify that two lines have the same length, two circles have the same radius or
diameter. If one of the objects changes, so will the other.
Symmetric – Selected geometry will be symmetric about another line, centerline, or edge.
Symmetric – Selected geometry will be symmetric about another line, centerline, or edge.
Parallel – The first line stays in position and the second line will move to become parallel to the first.
EGR 110 – Inventor Lecture #2
Geometric Constraints
Inventor provides nice illustrations for each geometric constraint when you pause the
mouse over the each constraint tool. Example: Parallel Constraint
Mouse paused
over parallel
constraint
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EGR 110 – Inventor Lecture #2
Showing, adding, and deleting constraints
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Show All Constraints - Right-click on a sketch and select Show All Constraints
Pausing the mouse over one
constraint will cause a pair of
constraints to be highlighted
to show which features are
related. Deleting one deletes
the pair.
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EGR 110 – Inventor Lecture #2
Showing, adding, and deleting constraints
Create a 2D sketch (include some lines that are not vertical or horizontal) and try the
following:
• Show All Constraints. Right-click on the Graphics window and select Show All
Constraints to show constraints for all features.
• Hide All Constraint. Similarly, select Hide All Constraints.
• Show constraints for a single feature. After hiding all constraints, right-click on a
single line or other feature and select Show Constraints.
• Delete some constraints. To delete a constraint, show the constraints, select the
constraint with the mouse, and press the Delete key.
• Add some constraints by selecting the desired constraint from the 2D sketch panel
and then pick the features that it should be applied to.
• Example: Pick the Perpendicular constraint tool and then pick two lines that you
wish to make perpendicular.
• Example: Draw two lines that are not parallel and then add a parallel constraint.
• Moving a constrained feature. Try dragging a feature that will not move. Remove a
constraint that will allow you to drag it. Re-constrain the object.
EGR 110 – Inventor Lecture #2
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Automatic constraints – Some constraints will appear automatically as features are
drawn as Inventor is trying to guess your intent.
Hold down the Ctrl key while drawing the feature to avoid applying the constraint.
Inventor automatically added a
Parallel constraint as this line was
drawn.
The automatic Parallel constraint
was removed by holding down the
Ctrl key.
EGR 110 – Inventor Lecture #2
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Scrubbing (changing a constraint) – If one constraint appears and you want another
constraint instead, try moving the cursor over the desired feature to which the new
feature should be constrained.
1
4
1
4
2
3
2
3
As line 3-4 is drawn above, the
Inventor seems to want to make
lines 1-2 and 3-4 parallel.
Moving the cursor briefly over line 2-3
will let Inventor know that you prefer to
apply the constraint that lines 2-3 and
3-4 be perpendicular.
Fully constrained objects – When an object is fully constrained, it can no longer be
moved. Inventor will change the color of the object when it is fully constrained. This
will generally not occur unless a point on the object has been fixed, since the object can
otherwise be moved to a new location. Later in the course we will often seek to fully
constrain sketches. Note that Inventor will generally not allow you to over-constrain an
object or to apply duplicate constraints.
EGR 110 – Inventor Lecture #2
Inferred points – dashed lines are used to indicate a vertical or horizontal position
related to another feature.
1
4
3
1
2
3
As line 3-4 is drawn, the dotted
line indicates that point 4 will
share the same y-coordinate as
point 1. If the dotted line does
not appear, briefly move the
cursor over line 1-2.
4
2
As line 3-4 is drawn, the dotted
lines indicate that point 4 will
share the same x-coordinate as
point 2 and the same ycoordinate as point 1.
Hint – If an inferred point is being applied that you do not want, hold down the Ctrl
key to remove it.
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EGR 110 – Inventor Lecture #2
Editing Tools
Several useful editing tools are
available on the Modify Menu
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Move and Copy – these two commands are quite similar in the way that they are used.
1.
2.
3.
4.
Select either the Move or the Copy tool
Use the Select button to select the feature(s)
to be moved or copied.
Select the top right arrow in the box to pick a
base point to copy from (perhaps the center
of a circle if you are moving or copying the
circle).
Pick an end point in the graphics window to
copy to. Pick multiple points to additional
copies with the Copy command.
Feature to
be copied
Base
point
End
point
EGR 110 – Inventor Lecture #2
Trim
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• Select Trim from the 2D Sketch Panel and move the cursor over the desired feature to be
trimmed.
• Options of parts of the feature to be trimmed will become dotted lines as you move the cursor
over them.
• Example: Sketch the object shown below. Add tangent constraints for the ends of each lines
with the circles (4 constraints total). Trim the inside portion of the circles.
dotted
line
Draw basic shape.
Do not draw lines
to look tangent!
Add a vertical constraint
to the center points. Add
4 tangent constraints.
Select Trim tool. Lines to
be trimmed turn dotted
when you pause over them.
Completed object
after trimming
circles.
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EGR 110 – Inventor Lecture #2
Extend – The command works similar to Trim for extending a feature (such as a line)
until it intersects with another feature.
Example: Select Extend and move the cursor over the top line. It changes color and
shows where the possible extension will go. Left click the mouse to accept the
extension.
2)Possible extension appears
1) Pause mouse
3) Left click to accept
over line to extend
EGR 110 – Inventor Lecture #2
Which sketch plane should
you use?
Recall that when you create an
initial 2D sketch plane, you
have a choice of planes to use
(refer to the xyz icon below
for orientation):
• xy plane – front view
• xz plane – top view
• yz plane – right side view
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xy plane
(front)
xz plane
(top)
yz plane
(right)
To determine which sketch plane to use, you should envision the solid model that you
wish to create and decide whether and extrusion in the x, y, or z direction would work
best.
See the next slide for examples.
Selecting a sketch plane
An xy (front) sketch
plane would work best
for this solid
A yz (right) sketch
plane would work best
for this solid
An xz (top) sketch
plane would work best
for this solid
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EGR 110 – Inventor Lecture #2
Orientation of sketch planes
When you select a particular sketch
plane, Inventor may rotate the plane in a
way that is not what you intended. This
is easily fixed.
Example:
1. Select the yz plane (right view)
2. Note the odd orientation as indicated
by the View Cube
3. Rotate the View Cube for the desired
orientation.
4. Draw the sketch
5. Extrude
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1. Select the yz
plane (right view)
2. Note the odd orientation as
indicated by the view cube
Select arrow to
rotate View Cube
3. Rotate the
View Cube
4. Draw the sketch
5. Extrude
EGR 110 – Inventor Lecture #2
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Quick check – Which sketch plane should be used in each case below? Circle Front, Top, or
Right in each case (or circle multiple choices if applicable).
Front Top Right
Front Top Right
Front Top Right
Front Top Right
Front Top Right
Front Top Right
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EGR 110 – Inventor Lecture #2
Multiple Sketch Planes
In earlier examples, a single sketch plane was used to create a 2D profile that was then
extruded to form a solid. In a similar manner, additional sketch planes can be added.
These sketch planes can be located on:
• Planar faces of a part
• Work planes attached to part geometry
• XY, XZ, or YZ planes that are part of the World Coordinate System
We will use the first option today (sketch planes on planar faces of a part).
EGR 110 – Inventor Lecture #2
Adding Multiple Extruded Features (Example)
• Open a new part file
• Create a 2D Sketch from the front view similar to the one show below (Sketch1)
• Extrude the sketch to form a solid and switch to an Isometric View (Extrusion1)
• Add dimensions if you wish
Sketch1
Extrusion1
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EGR 110 – Inventor Lecture #2
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Example (continued)
Now add another extruded feature projecting from one of the faces of Extrusion1 as follows:
• Select the Create 2D Sketch. Note that the message bar at the bottom of the screen shows
“Select plane to create sketch or an existing sketch to edit.”
• Select the plane where the extruded feature is to be added. There are sometimes several
choices of planes to select. Pause the mouse over the desired plane and a menu will appear
allowing you to pick the desired plane. Selected the desired plane (face).
• Once the plane has been selected, the object will rotate so that the selected face (and new
sketch plane) is parallel to the screen .
Pause over
desired face to
select other faces
New Sketch plane added to selected face
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EGR 110 – Inventor Lecture #2
Example (continued)
• Draw the 2D profile for the new feature to be extruded. It is important that features
on the new sketch are properly connected to the existing solid. This will insure that
the two extrusions are properly joined.
When drawing the box to the right, be sure that the endpoint (indicated by a green circle) of a
line or rectangle is picked to properly join the features. The features could also be joined by
separating them, adding a dimension between them, and then changing the dimension to 0.
endpoint
New Sketch plane added to selected face
EGR 110 – Inventor Lecture #2
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Example (continued)
•
•
•
•
Finish Sketch2
Extrude Sketch2 to create Extrusion2 – (Extrude is on the 3D Model menu)
Experiment with extruding in different directions.
Change Extents to To and pick the back face of the model.
Add Sketch2
Change Extents to To and pick back face of solid
After picking the back face you can see the effect
Select OK to accept. Final solid shown.
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EGR 110 – Inventor Lecture #2
Example (continued)
• Note that properly joined solids will not have a line where they were joined. A line
typically indicates that care was not taken to insure that an added sketch was properly
joined to the original solid.
Line indicates
an error
Properly joined solids
Improperly joined solids
EGR 110 – Inventor Lecture #2
Example (continued)
• Try editing Sketch1, Extrusion1, Sketch2, Extrusion2.
• Right click on the desired sketch or feature to in the browser to edit it.
• Some edited versions are shown below.
Right-click and
select Edit Sketch
or Edit Feature
Original
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EGR 110 – Inventor Lecture #2
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Quick check – How many extrusions would be required in each case below? Circle 1, 2, or 3.
Discuss the steps that might be used in construction the solid model.
1
2
3
1
2
3
1
1
2
2
3
3
1
1
2
2
3
3
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EGR 110 – Inventor Lecture #2
Background Color – A white background color is handy for screen captures (especially
for instructors). To change to a white background:
• Go to model mode (close sketch
to get out of sketch mode)
• Under Tools menu select
Application Options
• Select the Color tab
• Change Color Scheme to
Presentation
• Change Background to 1 Color