Cylinder with a hole / two insert mates

Forum|Forum|13 years ago
January 14, 2013
3 replies
8742 views

I have a little dilema. I have two cylindrical surface that are mated together by their outside surface using a insert mate. Then I align the parts again by using another insert mate to line up bolt holes. This totally defines the mate (i.e. turns it yellow) as you can see on the drawings. If thing don't line up quite correctly, I hit the flip icon to properly get them to line up.

I made a couple of changes and went back into my part to find that the part didn't line up correctly any more. When I flipped it, you can see the results on the second picture. Do I need to add a third mate to get this to stay as needed?

I ended up removing one surface from each mate (the one belonging to the assembly not the part being assembled) and used the move/roate to change the orientation of the part and rechoosing the surface to get it to turn out correctly (see the third picture).

Any input as to:

1. Why this may have happened.

2. Why can't it be correctly simply - without having to break the mates and rechoose the surfaces)

3. If you should always add the third mate to prevent thes from being changed (the part actually isn't actually fully restrained when there are two solutions to the mate)

Thanks, Dale

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Assembly Design

T

TomD.inPDX

17-Peridot

There is the "Allow Assumptions" for the case of fasteners that have no rotational alignment requirements. Often people will even leave screws rotationally free. No big deal. But if you have something that does matter rotationally like this leg, you need to click off the Allow Assumptions button and mate the orientation. The fact that this is on by default is what bothers me. I'd rather choose it when appropriate.

If you remove the Allow Assumptions, you should be able to add a 3rd constraint. You may need to click on New Constraint or it will overwrite the previous one. This assembly dialog lacks a lot to be desired. I find it cumbersome as all get out.

In general, yes, you can affect each contraint by their own merrits. The dialog use to be even worse, if that's possible

Dale_Rosema

Author

23-Emerald III

There was no allow assumptions to check or uncheck. It figured it knew what to do with only the two mates.

I had thought about that, but when I checked it wasn't there to uncheck.

T

TomD.inPDX

17-Peridot

So how does WF deal with "allow assumptions" ?

Sweet.. I did find comp_placement_assumptions *yes no in the current config.pro. I think I will set that one to no.

Patriot_1776

22-Sapphire II

Those 2 constraints, in and of themselves, are not enough to fully constrain that geometry BY that geometry. As it is, and as you see, there are 2 different "solutions" possible. Think about it. You must add a constraint of some type (align-coincident or align-orient, etc.), to completely define the part.

Dale_Rosema

Author

23-Emerald III

I understand, but the software is telling me that it is fully constrained.

Patriot_1776

22-Sapphire II

sorry, I worded it wrong earlier: It IS fully constrained.......it's just that you don't like the default "solution".

S

SylvainA.

1-Visitor

My 2 cents:

I'm not sure of how it works in Creo1.0 or 2.0, but in WF5 there are actually 4 ways to assemble 2 parts with insert+insert constraints (I've added align/mate constraints to get rid of default Pro/E placement):