Misbehaving mates

thomas_holford

I've made the following document public:  Octagonal pedestal

https://cad.onshape.com/documents/1d0aacd5ac1e425d97f4253b/w/c81d8434e8a846008ca85e4e/e/736a3a04075f4635934306ca

Question 1:  Is there any way to freeze the orientation of a part or assembly so that it appears in the same orientation when the document is closed and re-opened.  It also seems that OpenShape randomly picks a tab to use as a the document picture for the documents list.  Is there any way to make the documents list use a preferred tab/picture.

Question 2: I am try to assemble the parts in an octagonal frame (Assembly 1) tab.  If gotten the first four parts to mate, but adding additional parts in the orientation I want just isn't working.  Either I can't get the parts to mate in the orientation I want, or the mate disrupts the previous mates and distorts the geometry.  The mates functions just don't seem to be as intuitive or robust as they need to be, especially for larger projects with many parts and assemblies.

What mate functions or strategies do I need to use to produce the octagonal frame I'm trying to create?

nav

Hi @thomas_holford as explained by @andrew_troup, the fastest way to accomplish this is building your complete model using the circular pattern feature in parts studio, if for some reason you still want to use assemblies to recreate this part; I've checked your model and saw the mates you were using, OS is very unique about how assemblies are done, the Mate connectors feature is very powerful and once you know how they work, matting operations are really fast compared to other CAD packages. (When I first started using OS in assemblies I was doing what I believe you were doing in your model, planar mating faces to align, etc). https://www.onshape.com/videos/twio-mate-connectors



Try using the fastened mate for example, it removes all DoF from the mated parts. (Again faster to create this in Parts studio as mentioned by Andrew)

andrew_troup

@thomas_holford

Re your Qu2:
Mates in Onshape are not designed or optimised for what you're trying to achieve: they're intended purely to deal with relative motion.
There's a much simpler alternative, which is to "Circular pattern" the parts in a Part Studio. This will achieve what you're trying to do in a single feature.

If you then want to insert them into an assembly, maintaining their octagonal relationship, simply "Group" them in the assembly, and "Fix" one of them.

There's a Webinar laying out MultiPart Modelling which clarifies the different conceptual underpinnings of Onshape, relative to other modellers you may be used to, at https://www.onshape.com/videos/twio-multi-part
The audio could be better, but the content is golden.

andrew_troup

@thomas_holford
If I were modelling your pedestal, I would have only a single tab: a Part Studio

If you were intent on using Assemblies and Mates, it would be preferable that all parts be mated to their own connector rather than to each other:
You would need to create a circular array of connectors, which (off the top of my head - it's not something I've tried) would probably first require creating a circular array of construction planes.
Mating to adjacent parts is akin to building a house of cards:  tricky to carry out, and not resilient to future contingencies.

nav

Hi @thomas_holford as explained by @andrew_troup, the fastest way to accomplish this is building your complete model using the circular pattern feature in parts studio, if for some reason you still want to use assemblies to recreate this part; I've checked your model and saw the mates you were using, OS is very unique about how assemblies are done, the Mate connectors feature is very powerful and once you know how they work, matting operations are really fast compared to other CAD packages. (When I first started using OS in assemblies I was doing what I believe you were doing in your model, planar mating faces to align, etc). https://www.onshape.com/videos/twio-mate-connectors



Try using the fastened mate for example, it removes all DoF from the mated parts. (Again faster to create this in Parts studio as mentioned by Andrew)