Component Patterns 1

[drawoh]

I have just wasted the better part of a day trying to fix a messed up assembly model. Somehow, my constraints were being described by SolidWorks as overdefined. As far as I am concerned, they were not. When I deleted the overdefining dimensions, SolidWorks claimed that my assembly was now properly defined. I could easily see that parts were not properly constrained, and it was possible to move them around, proving my point.

Several hours of very frustrated hacking around later, I gave up. I decided to delete all my fasteners, and try re-installing them. I started this by deleting the component patterns.

Surprise! The problem went away.

Somehow, my component patterns were screwing up the assembly constraints on my model.

I put this down as a helpful tip because my problem is solved. I just wish I understood what happened.

JHG

 

[macPT]

To solve mating problems (not by deleting the components but by redefining the constraints with the components in the assembly) requires practice and careful analisys.

One thing I have learned is that "overdefined" can have different meanings and can drive you in wrong directions.

Example:
- you insert a part and make the horizontal plane of the part coincident with the horizontal plane of the assembly
- now you make the horizontal plane of the part coincident with the vertical plane of the assembly
- SW reports an overdefined assembly. In fact, that is not true because overdifened should mean that you have a set of POSSIBLE constraints, more than needed. In this example you have a set of IMPOSSIBLE constraints because a plane cannot be coincident with two orthogonal planes. SW should give different warnings.
- if you delete one constraint, the assembly is "surprisingly" underdefined (just because it was not realy overdefined).

Was I clear?

Another usual error is when you change the Aligned and Anti-aligned properties of matings. This can also drive you to incorrect overdefining information (in this case it is also a problem of a set of impossible constraints). When you need to change the orientation of a component, normaly you need to change the alignement of, at least, two mates (modify one mate, SW reports overdefining, change the other and now it's OK)

Regards

 

[drawoh]

MacPT,

You are quite clear, but I am aware of all this. An optimal constraint layout is...

* plane to plane,
* plane to edge or line,
* plane to point.

Alternately...

* plane to plane,
* concentric (round surface to round line or point),
* plane parallel to line.

Both of these control six DsOF. It is often hard to do this, but in the case above, I succeeded. In any case, if I had screwed this up, turning off the offending constraint would have fixed the errors, and left my components unconstrained Deleting the component pattern would have had no effect.

JHG

 

[macPT]

My first post as not correct. When there's a mating error an SW window pops up giving more detailed information about the problem. In this window, the information differs according to the mating error, being more clear than the unique icon in the feature manager window. If you read this information (which I normally don't do, sorry) SW gives you some hints to solve the problem. But I never tested this information to see if it always point in the right direction.

But in my opinion, to be more clear, SW should have different icons according to the mating error nature.

Regards