Problem in big assembly 1

[pablbalbi]

Hello everyone!
I am having a problem when trying to move parts inside a big assembly i have. The assembly has arround 540 parts, and 420 relationships.
The main problem is that i have a mechanism i need to evaluate by making it move, but whathever i try (by dragging, or by moving with reference system) i cant make it. I also try dragging a new part into the assembly, and nevertheless that part has no relationships, it won't move.

I´d appreaciate any help soon!

Thanks, Pablo.

 

[Updraft]

Without seeing your files there is a lot we don't know, but here are some good general tips:
1. Use subassemblies a lot. A large assembly file with mostly parts and few subs is a royal pain to work with. Besides, in all likelihood subassemblies would be physically built and then assembled into the top level assy so this also would be modeling the design intent.
2. Setup mates between the parts as you would when you assemble them on the bench into their subs.
3. If you have a subassembly with a flexible component, such as a cylinder, then give that cylinder an appropriate limit mate and when you bring that subassembly into the next level assembly make sure it is set to flexible so it can move through its range of motion.
4. When bringing in new parts or subassemblies make sure they are not just "fixed" which displays (f), but are instead mated as they would be physically assembled.
5. Apply the mates to a part or subassembly as you bring it in. Do not bring in a bunch of them and then go mate them as it is so easy to miss something.
6. Use the simplest mates that will get the job done.
7. Fully constrain everything that should not move, that way, at a glance you can see what is still free to move by looking for the (-) in front of the part/subassy name in the feature tree. (I even go to the trouble of using "Lock Rotation" on the concentric mates of my fasteners.)

I hope this helps.

- - -Updraft

 

[hendersdc]

In addition to Updraft's great advice, I have found that for some complicated cases I have not been able to drag mechanisms through their full range of motion without problems. In those cases I have used either separate configurations or separate assemblies which each contain only a portion of the overall motion in order to see the parts all moving together and check for possible interferences.

 

[Jboggs]

In addition to Updraft's excellent recommendations, lessons we have learned include:
1. All mates require extensive calculations of geometric equations with multiple possible "correct" results. It amazes me that they work at all! The more advanced the mate the more complicated the calculations - by an order of magnitude.
2. Avoid advanced mates if at all possible. For example, EVERY assembly in which we have used the Width mate blows up sooner or later. Haven't used it in two years.
3. Learn to use geometric features (like axes, planes, sketch entities, points, etc.) in your mates. They can be very useful, and I think the internal calculations are simpler.
4. Eliminate all mates that are not absolutely required. For example, a newbie might use a parallel mate to manipulate a part into an orientation, then later come along and place a distance mate on the same two surfaces. The parallel mate just became redundant. But SW doesn't know that. It still calculates it every time, along with its two possible correct results. And randomly chooses the wrong one. Eliminate redundant mates!
5. We are investigating this idea too: if a part is properly located and will not ever move in the future, what purpose do its mates serve? None in my mind. They could all be replaced with a single Lock mate. Or maybe just fix those "non-moving" parts and use no mates on them at all. There could be consequences down the road to that approach but its worth considering.

 

[Updraft]

Jboggs,
Your reply also made me think of something that can further simplify assembly mates. If a subassembly is completely static in the top level then so long as that sub is fixed (not flexible) its components do not need to be completely fixed. It might be a subtlety, but it pays to be aware.

Also, your comment about redundant mates is particularly good. There are times I will make surfaces parallel or even coincident, but then later edit that mate to be a distance mate. I much prefer this over adding the distance mate and then having to delete the previous and now redundant mate.

Another valuable tip I should have pointed out is the use of patterns in an assembly. This is so helpful for a set of fasteners (bolt, washers, nut) to just pick the one group and tell it to pattern using the feature pattern and then picking the hole pattern. I also will often pattern parts and assemblies instead of applying a set of mates. Rather than applying three mates to fully constrain the new instance I can fully constrain the new instance with only the one pattern. Even more valuable is that I can grab a whole bunch of parts and put them in this pattern - again one feature fully constraining a bunch of parts. That's a lot of bang for the buck, plus it can apply a multitude of instances. Patterns in assemblies are often underutilized.

 

[Jboggs]

Updraft,
Agreed! We are just now discovering the advantages of feature driven patterns. A very powerful and robust tool.