Concentric constraints in assemblies

[Anonymous]

This was done in Inventor 2018.

I think I understand one of the problems with my understanding of constraints.  Assembly constraints seem like they are 3D constraints, when all I really need are 2D constraints.

For example, I have a NEMA-17 stepper motor.  It has a mounting ring.  I want to cut a hole in a board on which I will mount the motor.  So I create a mate, in which the flat face of the motor is mated flat to the surface of the board.  But now I need to make sure the center of the motor shaft, which is the center of the concentric mounting ring.  But any attempt to use an insert constraint gives me an unsolvable solution.  All I want is a way to say "the center of this circle is coincident to the center of this other circle".  Nothing more.  A 2D constraint.  Yet it seems that it is trying to do a 3D placement for the two circles I select.  I actually have several components that need coincident centers, yet there appears to be no simple mechanism to give me a 2D constraint for concentric points, or any points, for that matter.

I have attempted to create a Pack & Go and hope that I got it right.  I have the following:

a 30" square plywood board, which at the moment has one hole in its center, which is the diameter of the mounting flange of a NEMA-17 form-factor stepper motor.  I want the flange to line up with the hole, except, of course, the hole has to be slightly larger than the flange (perhaps 0.1mm is sufficient).  The hole should be fairly accurately cut, and in 1/2" plywood I will use a 150W laser cutter.  It takes two passes.  The first pass cuts about 1/4" deep,  then I drop the Z-axis down 1/4" and redraw the cut line, which causes the laser to focus halfway down the cut. 

I wanted to add the flange to connect the 2' arm to the stepper motor, and the only way I could get it was to form an insertion constraint between the hole that ends up next to the arm to match the hole in the arm, which is a very clumsy way to ask that the centers be coincident, which is all that I need.  Then I wanted to place the large rotating bearing concentric with the hole in the 30 x 30 x 1/2" top, the stepper shaft, the hole in the flange that is supposed to connect the shaft to the arm, etc.  For some reason, it stopped dragging as I was trying to get it into an approximate position.  Finally, I want to create a mate between the arm and the large flat bearing, and between the other surface of the flat bearing and the 30" top, so that the flange connected to the arm fits over the shaft.

All of this should be trivial.  None of it seems to be.  If I am using other constraints, such as mate constraints, to manage my Z-axis connectivity, then I only need 2D constraints to handle the concentricity. 

The goal is to create a camera that can be swung from one side of a student to the other, in order to read the material the student is working on.  The purpose is to create a "tutoring station" that lets high-risk volunteer tutors (that's me, and pretty much all of the tutors in the school district) continue to help students while reducing our exposure (I, personally, have five comorbidities with COVID-19.  I had to give up tutoring in the spring semester, and want to resume it, and remain safe).

[JDMather]

I cannot Extract the zip file.

Can you Attach the individual part files (I assume only two are needed for this particular assembly constraint) and the assembly file?

• 30" square plywood board, 
• mounting flange

[swalton]

An Insert constraint controls 5 or 6 degrees-of-freedom (DOF) between two components.  It makes two circular edges concentric.

In your case, you should select the edge of the hole in the plywood and the edge between the cylindrical pilot surface and the bolt flange on the stepper motor.  That will make the two edges concentric, and eliminate 5 DOF between the two components.  If you pick the lock option, you will eliminate the remaining rotation DOF too.

You could keep the Mate between the plywood surface and the  motor mounting face and then add a 2nd mate.  The 2nd mate would use two cylindrical surfaces, like the motor shaft and the hole in the plywood.  Add a 3rd constraint to control rotation to lock all 6 DOF.   

[mcgyvr]

Sounds like you simply need to use another mate (axis of stepper shaft to axis of hole). 

Or depending on your files you don't need the initial mate and can just use an insert constraint. 

As stated your zip file doesn't open for us to see your files..

Post the stepper motor and the mounting plate if the above doesn't answer your question.

[johnsonshiue]

Hi! Another easily overlooked Mate type is called Cylindrical Face Mate. For example, you have a shaft needs to penetrate a hole and the diameters are the same. You can easily create a Cylindrical Face Mate using Mate constraint ->select the cylinder face on the shaft via Select Other -> select the cylinder face on the hole via Select Other.

Many thanks!