Onshape Multi-Part Studio Exercise

peter_cuthbert

Hi Folks

To furher my education I have been working through the OnShape Multi-Part Studio training pack.  Once into the student exercise I have drawn the vice object as instructed.  The instructions include adding constraints such aas tangents, parallel, etc. in particular places.  However, in the background the software has been adding buckets of constraints too and eventually the whole drawing goes red and tells me that "The sketch could not be solved". My usual practice when faced with this problem is to hover the cursor to find the constraints and then slowly begin haphazardly deleting especially where there are three or so of the same constraint.  The problem of this approach is that I have no real idea of which one to choose as the starting point.  Thus sometimes the removal of a constraint causes the drawing to collapse.

So is there a logical approach to this process of de-constarining a drawing back to a state that can be solved?

The stalled exercise is to be found here:

https://cad.onshape.com/documents/d1c7ac4d09a4b2224e489fe2/w/1222205351bc745918bde09f/e/0230477aa2ac4f8d642baebf

Many thanks

Pete

Matt_Shields

I don't know if there is a repeatable best way to go about de-constraining over-constrained sketches, but the conflicting constraints are all visible.  It's worth mousing over each one to see which sketch elements pertain to the conflicting constraints.  In your case, I see a parallel that shouldn't be there...

matthew_stacy

@peter_cuthbert, one thing to familiarize yourself with is "version history" (versioning, branching, merging).  You can easily roll back your design history to a point in time before the sketch turned red.

I also advocate breaking geometry into smaller, simpler sketches.  In your case, imagine one sketch per part.  They can still be related to one another and there are tricks like applying the "Use / Project" tool to create construction geometry, for example to constrain a circle or other entity in your current sketch equal in size to a similar entity in a previous sketch.  Variables offer another avenue for creating relations between sketches.

Another tool in your arsenal is to hold down the <shift> key while you are sketching.  This turns off the auto-constraint feature, so that you can manually place the exact constraints that you need, precisely where you need them.  Think of it as turning off the cruise control in your car when you get into heavy traffic.  More effort in exchange for greater control.

Good luck.

peter_cuthbert

Good Morning Matt & Mathew

Thank you so much for your responses to my question.

The idea of watching out for the underlying geometry had somehow slipped past me but is obvious now you mention it.  Having that in mind I found the erroneous Parallel constrain almost immediately.

I am also in favour of smaller simple sketches, but in this one instance the whole point of the training exercise was to develop the whole item from a single drawing.  I am not sure that the training session has convinced me of that as a good strategy, but thanks to your observation of using the Shift key while sketching I am sure that I will avoid these kind of problems in the future.

Thanks again

Regards

Pete