Mates and cylindrical parts

[Standing]

When mating cylindrical parts that only require 2 mates, do you leave off the third mate? Out of 19 SolidWorks users here, we have only one person defining all 3 mates for dowels, washers and screws. He says he does this because he can look down the tree of a 500-part assembly and tell if all required parts are fully mated. We cannot tell the difference between a washer and a relay by looking at the part number in the tree. Some of the persons that do not define all 3 mates for cylindrical parts complain that someone is moving their parts into space. I was wondering if any of you complain of others moving your parts? I think that not mating all 3 mates is linked to parts moving in space, but cannot prove it. Because, they miss defining a critical part location I think that if someone moves a part in a subassembly, could move other parts, which are not fully defined. Bradley

 

[MadMango]

It only takes 2 mates to locate a cylindrical part in space, if you use Concentric and then a Coincident/Distance mate. The 3rd mate would probably be a Parallel mate to lock the cylindrical part from rotating in the hole. Sometimes, you don't want parts fully mated, especially if you want moveable/flexable sub-assemblies.

With that said, I usually use 3 mates for rotational parts, but make good use of small sub-asseblies. Some people complain about assembly problems where there are too many mates, but usually I only see this when they have large (~250 parts) sub-assemblies. "The attempt and not the deed confounds us."

 

[BBJT]

It all depends on the size of asseblies you deal with. The more mates in a assembly the more overhead your adding. I recommend to our SolidWorks comminity here not to at the third mate. Our assemblies 2nd level assemblies have 2000 to 3000 components in them and I think it would be safe to say that ruffly half of that is hardware. That would be 1000 to 1500 extra mate that are not needed.

BBJT CSWP

 

[macPT]

I usually I leave the component free to rotate. Sometimes it's really important to do that, if you want to do some simulation o moving parts.

But if there is some angular relation between the cilindrical part and other parts I use a third mate.

I normally use a third mate for fasteners, so they can have the proper appearence in the drawings (otherwise the heads will show in strange angles).

Regards

 

[BBJT]

So in real life all the heads on your fastners show up perfectly alligned with no weird angles? The way I look at it is a fastner is always going to turn. You ca tighten it, loosen it, stirp it, etc. That is just my opion though. Like I stated in my above post my biggest reason for not doing this is for performance and time issues. BBJT CSWP

 

[SBaugh]

If your using that many parts BBJT I could see why you wouldn't add the extra mates.

I most all cases that I have been in, my assemblies never exceeded 100-200 parts. My preference is to full define everything whether its an assembly or sketch. It helps to keep things from moving later, unless thats what your after.

It comes down to the users design intent and overall preference. If you don't use the proper mates for your assemblies you will see some freaky things happen when you move a component in an assembly. Which maybe what your seeing Bradley.

In real life when we as designers and engineers design our ideas, we design them theoretically perfect. In the perfect world there is no fastner that will ever strip, you only have to tighten it once and it lines up with all the others perfectly.

That was the first thing I was taught in college "everything is drawn theoretically perfect".

Best Regards, Scott Baugh, CSWP
3DVision Technologies

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[dhinners]

Here is another benefit of adding the third mate. If you work with several configurations of an assembly, it is easy to get some of your mates suppressed. Then the parts can get moved around by accident, especially if your configurations are for different assembly positions. The third mate allows you to quickly & easily visually verify that all your parts are fully constrained.
Again, this argument fails if you want dynamic assembly motion. To get around that, I try to use a dimension driven mate (i.e. distance or angle) to drive my different assembly position configs.

 

[EdDanzer]

We do assemblies up to about 2000 parts. After a couple of bad and expensive experiences created by leaving mates out to save a little time, I require all parts to be fully mated. At the time you start a project it may not make a difference, just wait a few years and revisit it and you may become painfully aware of why it is best to complete the assembly mates. If rotation angle, or position is to be varied, NAME the mates, it can save more time than it takes to do it.
Naming mates, feature, and configurations will help during collaboration, after memory failure, or after the creator is gone. Using planes and axes for mating will allow greater flexibility when changes need to be made, and simplify repair when things go bad.

 

[tbcad]

We define all freedoms of movement whether it be a fastener or a pump or whatever. One thing to check on your issue is if you are using a temporary axis to mate to and if you are loading parts lightweight. This can cause parts to disperse across the screen. A CTRL-Q (forced rebuild) would clear it up if that's the case.

 

[CajunCAD]

Are any of the parts that move off into space constrained by adding the "fixed" constraint rather than constraining?

Have any of the moving parts been modelled in the part file at a location away from the origin and then later moved to the origin?

If so, parts that are truely mated will retain the desired position in the assembly. Parts that are inserted and then have their position fixed will move.

 

[DetroitPickles]

I fully define everything, but like SBaugh, I don't have 3000 part assemblies. It is more like 300. I do this because I was used to doing it on Pro/E, and like a few others, I can tell pretty quickly if everything is set. If I see a minus in the FM, I don't really know if it is just the rotating mate or nor that is not defined.

That, and ever since SW 2001-plus came out and "cancelled" any overdefining mates my co-workers created in previous versions, I have a feeling that someday they may "require" everything to be fully mated and defined. I don't want to go through ALL that again.
Mr. Pickles