Fasten mate to origin

BRS

Hi,
I've been using Onshape for a little over a year and there is one thing I would really like to do, perhaps someone has a way or there is a script out there.  

I often end up in the situation where I have a part/sub assy that is correctly positioned and orientated in an assembly but is not tied to any parts, its just floating there.  In those cases is there any way to directly place a fastened mate between it and the assy origin with the correct x,y,z and angular transforms so that part can never move around?  

There are many work arounds and obviously have been working with them but feel it is slowing me down compared to connecting in place to the origin right there in the assy without tinkering in parts studios etc.  I've checked with a few people here that are decent users with many years for and they just replied with "I wish".  Hoping we are all missing an obvious answer.

Thanks
BRS

shawn_crocker

I would also like to do this.  Take a look at this improvement request I made awhile ago.  https://forum.onshape.com/discussion/16084/add-assembly-origin-to-a-group-mate.  I wish we could just add the assembly origin to a group mate that also included the item in question, it would solve the whole issue because the item could still move in relation to the assembly origin if changes where made of the items level.

NeilCooke

The workaround here is to add a small revolved surface (so it has no mass) to the origin and group to that. 

shawn_crocker

I use something like what @NeilCooke is suggesting.  I will sometimes use a mate connector in the part studio attached to the part studio origin.  Then attach that connector to the assembly origin.  Something I have noticed about assembly origins is that an assembly origin will cease to exist if the assembly is inserted into a top level assembly.  Anything in the assembly that is counting on the origin to evaluate, will now be loose in the top level assembly.  I'm feeling this is a good spot to get a feel for this issue as possibly being intended or if it is noted and scheduled to be fixed.

S1mon

Fix mates are only honored at that assembly level. It's definitely one of the Onshape oddities which drove me the most crazy when learning how to work with assemblies. At each assembly level, you really need to think carefully which instance is going to be fixed and how it's going to be fixed to the origin.

It's important when dealing with the non-Onshape world to respect assembly coordinate systems. It's way too easy to not have things locked down in an assembly and then they can accidentally get moved around. At least now there are icons indicating when instances have degrees of freedom.

I learned this over and over the hard way dealing with imported assemblies which had a bunch of different levels. Also the way that group mates work with subassemblies has taken me some time to get used to.

You may find some of these improvement requests interesting:
https://forum.onshape.com/discussion/16811/default-offsets-for-fastened-mate
https://forum.onshape.com/discussion/16995/preserve-prioritize-mates-in-lower-level-assemblies
https://forum.onshape.com/discussion/17829/allow-fix-constraint-to-be-maintained-when-inserting-into-a-parent-assembly
https://forum.onshape.com/discussion/16515/import-and-group

BRS

Ya, I had put an extra body at the origin that emulated a triad in as a work around in some of my top level assemblies last year but was not a fan of that approach for a couple reasons. I didn't make that method up, got from a coworker with more Onshape experience. Like you say, it is just a workaround, but it will work if you really need to do it.

I did a larger project in Onshape last year and the 2 things I wanted most were in assembly - the fact there was no way to know which parts were unconstrained (which is basically fixed now, thank you - that saves huge time) and this issue of constraining parts/subassemblies to the origin.

Shawns method would work for me, as well just a toggle setting in the fasten command that locks it with offsets and rotations in place.  Everything is known about its position in space, just need a way to get the transforms into the constraint without a measuring/rekeying manually. Would work for any fasten, not just to origin so would have other uses if OnShape ever thought about adding the functionality.