I think I have broken a context

martin_kopplow

I have a little assembly with lots of similar parts lined up at certain distances from each other. For production purposes, I wanted to make a lasercut jig, so they could all be easily positioned in place while the glue sets. Easy enough.

I did not want the jigs to be part of my assembly, though. So I designed them in context, but kept them in their own document that resides in a "Fixtures and Jigs" folder which has a shared link (accessible from the laser cuttung workshop), other than the assembly. Assuming the context would be established via the in-context sketch, I later deleted the jigs from the main assembly, because they were not meant to show up in any drawings and BOM anyway. Everything looked fine so far.

After a while, I needed to increase the thickness of some of the lined-up parts and therefore the jigs needed to be updated. I noticed, that after making these changes and creating a new version, my in-context jigs did not follow. I get a little blue dot indicating there's an update, but when I update the context, someting strage happens: I get a message asking me to set primary instance of context …

… but there is no menu item for doing so in the context menu.

If I go to the assembly, there is no trace of the context whatsoever …

… and consequently no item in the instance list and of course no context menu, too. I cannot set primary instance there as well. So I ran into a dead end.

Could it be the context management has just lost it? And if so: Is that a bug or did I do someting wrong? Is it because insertion of in context objects does only work on surfaces and bodies, not on sketches? Would that mean we shouldn't expect context based on just sketches to ever update with design changes? That would make the concept of in-context sketching questionable, then.

For tis time, I'll probably have to make new jigs, but I'd like to avoid such turbulences in the future.

EvanReese

This is intended behavior, not a bug. It's not intuitive, but once you get it, you get it. The primary instance needs to be in the assembly for the context to update. You can fix it by adding any of the parts from your jig to the assembly (in the right location) and right click that and set it as the primary instance.

The reason for this is that parts can move in an assembly even if they are from the same part studio, so Onshape needs just one part to be the "real" source of truth about the orientation of the part studio relative to the context.

martin_kopplow

@EvanReese

Okay, I get the connection, I recognize a workaround for my issue, and I confirm it is not intuitive.

Why must the primary instance be a part? It would be more intuitive if the primary instance (or then primary reference) could also be a sketch, or even better: A MATE CONNECTOR. We can already place a mate connector in the assembly and create an in-context part on it, usually starting out with a sketch. There is already a connection. It would only be logical, if the definition of the primary reference (necessary source of truth) could be made via the mate connector, then. That would allow references to be created, even when the parts are (not yet) existing in an assembly, with the result of such parts also following updates from the assembly as one would expect for in-context parts.

My major grief here is that in the current state, a connection is broken without any notice. Had I not checked the dimensions in the referenced drawing, wrong jigs would have been manufactured.

EvanReese

I think the primary instance can be a sketch. I think that's a great use case too. You could make a big sketch that drives the positions of major things and hang the rest of the design on it. Care to share where it's not working for you?