Using group and sub assemblies

guy_rogel

After a very expensive mistake in a project , I have realized there is a major logic problem with sub assemblies in on shape.
When inserting a sub assembly to a top level assembly it is possible to "Group" it. But this will only lock the position of the sub assembly parts. A change in the location of one or more parts in the sub assembly tab will not reflect at the top level assembly tab.  this means there is no option to have a sub assembly linked to it's tab in the same document.  I find this to be very very trubbling. what is the point in having sub assemblies if they do not reflect correctly.
I think there must be an option (I think it should be by defult) to make sure sub assembly in  the top level will be the same as it's TAB
It cost me more then 5000 USD to find this logic issue.

UPDATE
please see my comments how this can be solved

MBartlett21

Absolutely!

This sometimes seems to happen with linear patterns of assemblies as well.

lougallo

@guy_rogel We will reach out. Not a place to post an issue you had here when we can look at what happened.  We will be in touch soon.

guy_rogel

Not so major....

I now use a very simple (not nice but simple) solution to my problem
If I need to move a sub assembly which is not fully defined (for example an imported PCB ) in a top level assembly I :

1. Group it first
2. use mating to move it wherever needed
3. Delete or supress the group mate to make sure any changes in the sub assembly will reflect in the top level assembly

not the nicest solution but works
use the group mate with care
Guy

alnis

@guy_rogel if you're working with imported data, it's best to either use the "composite part" feature to create a single composite part for the whole PCB or whatever it is, or insert it into an assembly of its own, fix one part, and group all of them. This will let you drag/mate it however you want in other assemblies

Making a composite part (good for imported stuff or things you model, "closed" makes it a single "thing" with one color for everything, not "closed" preserves colors)



Adding the parts to a subassembly, then grouping. Be sure to fix so that they aren't moved from the default position! That will let you add stuff later by directly clicking the green checkmark to insert in a consistent location, then grouping, rather than having to mate everything individually

guy_rogel

Thank you Alnis
I will defiantly check this soon

MBartlett21

There is also an option when you import the part as well.

john_mcclary

I agree, group mate is nice, but it ignores subassemblies and goes right into the parts within the sub assembly. Fixing them in the same place they were when the group mate was created.

This is not intuitive for subassemblies and is always a confusing issue. I think group should throw a warning when someone selects a sub assembly. Or just prevent the ability to select sub assemblies when creating a group mate.

tomasz_szwarc457

@alnis
Hi,
I just moved to OS from other cad and the solution with "composite parts" is not really well suited for working with imported parts.
Imagine you purchase your PCB as an single product and you need to assign an Part Number for the whole PCB (then also Vendor and Supplier PN for the BOM purposes)

When you try to release such "composite part" in OS you're asked to apply Part Numbers to ALL items in the composite parts.
I.E. you must assign part numbers to all bodies in composite part - an complete waste of resources.

When I buy an complete PCB assembly from a supplier it has an SPN assigned to it and just ONE part number.
Now - in OS - when you'll export a BOM it will turn out to be excessive complex.

NeilCooke

@tomasz_szwarc457 try closed composite

Mark_Wyss_wyssion_GmbH

Hello, I am new with onshape. But i do not understand the Assembly and Sub-Assembly logic. When I do have an Assembly with Sub-Assembly and i move a Sub-Assambly - why is it just moving the part of that Sub-Assembly i grap, and not the whole subassembly? (not the same logic like SolidWorks?) br Mark

NeilCooke

https://forum.onshape.com/discussion/comment/110094#Comment_110094

The difference is that "Fix" is not a constraint, it is only used to stop the current assembly from floating around and does not transfer up to the next assembly. In the subassembly, fix one part (to stop it floating) then use Group.

eric_pesty

https://forum.onshape.com/discussion/comment/110094#Comment_110094

You can also use the "lock" function so that the sub-assembly behaves more like SolidWorks.

nick_papageorge_dayjob

https://forum.onshape.com/discussion/comment/110094#Comment_110094

It's designed like real life. Let's say you have a door knob subasm inside of a door asm. In ProE/Creo, the knob subasm would be static in the door asm. In OS, you could turn the door knob and it would move the latch, and you could do this regardless of how far the door is rotated on its hinges in the top level asm. Its super easy to do real-life motion, but it does require changing the thought process of how assemblies are built.