Assembly Mating Don'ts

SolidWorks tries to be flexible and allow you to mate parts together in many different ways.  Just because you can do it doesn’t mean you should. You usually see list on best practices(the positives), but I haven’t seen a list on things not to do.  This is not an all includes list, but here are some common things that bug me.  I may add to it later if there’s interest in this topic.  I tend to not to follow rules unless I know why…so here’s some rules and their Whys….

1)     Never Mate Point to Point:  I must admit I’ve done this before, but I was under the influence of frustration. In general there’s very little reason to do it, except for maybe trying to simulate some motion, even in that case I would try to use something else first.  If you use this method, then in order to fully constrain your part you end up having to put more mates on it than you should need to.  This makes a messy tree and is harder to trouble shoot when things start going red.

2)     Don’t fix multiple parts:  Why would you do this, other than laziness, which by the way can be a valid excuse at times.  Again this will make it harder to trouble shoot down the road.  Especially when you decide you need to mate 2 fixed components together. J  I know that sounds obvious… but it’s easier to do than you think.

3)     Don’t leave over defining mates:  You may make a part parallel to something.  Then later you know what distance it should be at and so you put in a distance mate (you should have edited the other one, but I’ll forgive you if you clean it up later).  At this point, SolidWorks says no problem I can figure that out…however your part is really over defined and this will show up of you try to flip the alignment or it may show up as an error (most likely a yellow bomb) if something else goes wrong with one of your parts.

4)     Avoid mating edges & axis:  If you have perfectly beautiful flat faces or 2 cylindrical faces for concentric, why would you make things harder for yourself?  Edges are more likely to change, edges and axis are harder to see, find, click on, etc…   There are some good reasons why you may want to make axis together or to something else, but if your scenario is a screw and a hole you’re not going to win that argument with me.

5)     Avoid Multiple configurations of Angular Mates:  Sometimes this works just fine, other times the align/anti-align can drive you absolutely crazy.   Let’s use the example of a hinge.  If you want to shop it in several different distinct positions it may be more robust to mate the flexible end of the hinge to a plane and control the angle of that plane in your different configurations.  This doesn’t always work, but it gives you something else to try if you’re having problems.

6)     Don’t suppress mates you don’t want:  If you don’t want it, throw it away.  If you want to try something document (comments, change names, etc..) what you’re doing.  If you just suppress it you’ll leave it there until you forget why it was there and suppressed.

7)     Don’t Interchange the words fix and constrained: A part is either fully constrained (fully mated in place) or fix, they are not the same.  It will make things much easier for someone to help you figure out what’s gone wacky if you use these terms correctly.

Before you go ahead and do one of these things I warned you not to do, just ask yourself “why do I need to do it that way?”, if you have a decent reason and understand and are willing to accept the pitfalls….than go for it.  I hope this saves you some headaches.

Comments

[Corporal Willy]

Wow Christine, you made me scared about teaching mates to my students. You have my interest and attention and by all means please let me know more so I can teach my students without errors. Thank you.
cplrich@cox.net

[Christine Vrooman]

Don't be too scared. There are exceptions to every rule. I work with a lot of large assemblies and spend a good amount of time diagnosing and figuring out mates. The best way it to mate thing together the way they actually work or based on design intent (symmetry).
Thanks for the feedback.