Choose tangency point for a circle and flat surface

[ejenner]

I need to set a flat surface tangent to a hole (so a screw will go thru a slot). When I try to make the constraint, it ALWAYS selects the tangency such the the slot is next to the hole, instead of over. There are two valid tangency points (either side of the hole) but I cannot find any way to tell it to use the other point. How do I instruct the program to set the tangent constraint based on the other valid location?

[TomD.inPDX]

There might be better ways to do what you are trying to do. But for the question at hand, you could add a distance or parallel to a plane to either lock or limit movement. What happens if you "flip" the constraint? Are there still degrees of freedom at the point of adding the tangent? A little more information could be helpful. Post an image maybe?

[ejenner]

Flip is not an option. Greyed out. And the tangent is the last degree of freedom in the system.

[TomD.inPDX]

Try putting in the tangent 1st. You should have some degrees of freedom left. You can drag the component to see what it is actually being constrained.

With the object you are describing in the other thread, are you sure you don't want to use Mechanism contraints?

[TimBrotherhood]

Have you tried the peg in slot mechanism constraint? The attached demonstration has a peg in slot assembly constraint connecting a datum point in the centre of the peg and a datum curve between centres in the slot.

The video was captured in the Creo Parametric Mechanism module with a servo motor driving the crank.

Video Link : 3840

[TomD.inPDX]

Tim, I cannot read the file since it is an education version file.

In Creo 2.0 they simply call that mechanism constraint "slot". There seems to be quite a few options to this constraints type. Funny thing is that by default, it acts like a gimbal with motion along a "path" if the path is selected. I can foresee quite a few uses for this.

[ejenner]

I have abandoned trying to do it this way at all and am doing it with a different geometry.

[jflatt]

The ability (or more inability) to correctly constrain assemblies is one of my biggest gripes about Pro/E/Creo. The inability to chose internal or external tangency has caused me to pull what little hair I have left out. I was hoping there would be a better answer in this thread. As such, I did find a crude, ugly, and wholly distasteful solution that worked. At least in this assembly.

Since my tangency to the hole always came out on the wrong side of the planar surface, I created a plane in the mating part that was offest from the planar surface by the diameter of the hole. Then I made my tangency constraint to the plane instead of the surface. It worked at a visual and functional level. But now I've got superfluous planes in the model, as well as parametric dimensions on the print that need to be ignored, and if I change the size of the hole I'll have to go back and manually change the mating part so the assembly comes out right. Not pretty, but I it's the best I could come up with.

[TomD.inPDX]

Hello Jim and welcome to the forum.

I like your solution. I use to be very shy about superfluous datums, axes or points on a part but I've learned that once they serve a purpose, the are no longer superflous.

I work very hard to make sure my models are stable from a sustainability perspective. To me, this is much more important.