Unit 05 · Lecture 9
Assemblies: place, rotate and ground parts
Parts become products in an assembly. This lesson places the first three parts of a tapping mechanism, orients them, and uses constraints to remove their six degrees of freedom.
Video 18:57Reading 9 minUpdated 26 October 2026
What you will build
The base of the tapping mechanism: a grounded ground plate with two rail stands constrained beneath it, holes aligned for bolting.
You will learn
- The Standard (DIN).iam assembly template
- Place and the right-click rotate X / Y / Z 90°
- Six degrees of freedom and how to display them
- Grounded parts
- Mate vs. Flush, face normals and axis alignment
Before you start
Have the tapping mechanism part files ready (ground plate, rail stand). You should know part modelling from Unit 03.
Step by step
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01
Create an assembly file
0:40Choose Standard (DIN).iam, the Inventor assembly template. The ribbon now has an Assemble tab. Instead of Start 2D Sketch, you begin with Place.
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02
Place and orient the ground plate
1:26Click Place and open ground plate from the tapping mechanism folder. Before you click to drop it, right-click for Rotate X 90°, Rotate Y 90° and Rotate Z 90°.
To predict the result, imagine holding the chosen axis still and turning the other two around it. Rotate X 90° sends Y to the top and Z to the front. That lays the plate flat. Left-click once and press Esc.
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03
Place two rail stands
5:53Place rail stand with the chamfered edge pointing down (Rotate X 90° again), then click twice to drop two copies.
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04
Show degrees of freedom
8:10Go to View → Degrees of Freedom. Each free part shows six arrows: translation along X, Y and Z, and rotation about each axis. The goal is to remove them all, or keep only the motion you want.
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05
Ground the base part
9:37Right-click the ground plate and choose Grounded. A pushpin icon appears and all six freedoms are gone. It plays the role the sketch origin plays in a part: the fixed reference.
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06
Mate the faces
11:04Open Constrain (types: Assembly, Motion, Transitional, Constraint Set) and choose Mate. Click the top face of a rail stand, then the bottom face of the plate. The arrows shown are face normals. With Mate they point at each other and the faces meet. Up and down movement is now gone.
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07
Use Flush for side faces
13:15Mating the front faces pushes the rail stand out in front. Choose Flush instead: the normals point the same way and the faces line up in one plane. Do the same with the right-hand faces. If you pick the wrong solution, use Edit Relationship to fix it.
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08
Align holes by axis
16:53For the second rail stand, mate the faces first, then click the inner cylindrical surface of each hole to align their axes. Do this for two holes. Aligning centre points instead lets the part pivot loosely, so always do faces first, then axes.
Constraint logic
Relative constraints chain to the ground
Rail stands are constrained to the plate, and the plate is grounded. Unground the plate and everything moves with it. It’s the same chain-to-origin logic as a sketch.
Mate or Flush
Both put two faces in one plane. Mate sets them face to face with normals opposed. Flush sets them side by side with normals aligned. Picking the wrong one is the most common assembly error.
Common mistakes
- Leaving every part ungrounded, so the whole assembly floats.
- Mating side faces that should be flush, which throws the part out of position.
- Aligning hole centre points instead of axes.
- Constraining axes before faces, which makes parts spin into odd positions.
Practice exercise
Unground the ground plate and drag it. Both rail stands should follow. Ground it again, then turn on degrees of freedom and confirm that no arrows remain.
Check yourself
What file extension is an Inventor assembly?
.iam.
How many degrees of freedom does a free part have?
Six: three translations and three rotations.
Two faces should lie side by side in one plane. Mate or Flush?
Flush.
What do you constrain first when aligning holes?
The faces, then the hole axes.
Want the graded version? Take the 5-question lesson quiz in the course player after the video.
Written by the CADsmit instructor from the lecture recording and checked in Autodesk Inventor Professional 2027. Last updated 26 October 2026. Spotted an error? Tell us.