It would seem obvious to me that a sketch with no relations will solve faster than a fully defined one, because there is nothing to solve! However, there may be an intermediate case with partially defined complex sketches, where the solver might struggle to reach a solution and therefore take longer.

In general I would go along with the others that say fully define sketches. There is nothing more time-wasting than an unpredictable outcome!
Actually, that’s one of my major gripes with Solidworks, that fully constrained assemblies don’t always behave predictably – especially multi-level ones with different sub-assy configs, flexible sub-assys etc.

Devin: about the myth that part move by themselves: parts don´move until your manager (or your idiot colleague) grabs the mouse and tries to rotate the view. It is all about reliability. How sure are you the model is correct when you´re about to spend 10 times your yearly salary on moulds? Believe me, you want to fully mate parts and fully define sketches.

Jeff: seems odd to me that there is no simple way to fully define splines AND be able to manipulate them as though it were clay. Another myth to bust: the one that says that SW is user friendly.

Under defined sketch/es can cost you 10′s if not 100′s of thousands of dollars never mind the loss of time etc. During crunch time when your brain is almost fried and drawing are due to be released for tooling… All you need to do is to slightly move a line or a point in one of your under defined sketches. How would you even know what you did or moved and even if did find what moved how would you place it back where it was? Ctrl Z doezn’t always work the way you want…

Blue sketch to me is like a red cloth to a bull. When I teach, this is number one rule I demand my students to learn. NO BLUE SKETCHES!!!

Perhaps, I would agree on blue sketches during conceptual stage when nothing is critical, but for production……no way, keep em black I say.

My guess is that anyone saying sketches should always be fully defined isn’t doing a lot of work with splines (such as surfaces-heavy modeling), and certainly not doing lots of wild editing of swoopy geometry. I typically don’t define splines with anything more than relations. I often go into the sketch and push/pull spline points to tweak the overall form of a surface fill/loft/sweep/whatever.

Further, this has never caused problems of things moving around. Sure, if you’ve got a point of a sketch segment pegged to exterior geometry (and little else defined), when you move that external geometry, part of your undefined sketch will also move. But isn’t this also predictable (and even sometimes desired)?

Matt- I agree with you. Another myth to bust, the one that says Parts with no Mates move by themselves in SW Assembies.

Great post.

Devon

I think you and Ray are talking the same thing when you say ‘partially defined’ and he says ‘underdefined’ (not undefined). I’ve seen underdefined used in this context before, and while it’s not perhaps as clear as saying ‘partially defined’ I’ve always taken it to mean the same.

My guess is that when users complain about ‘completely undefined’ sketches moving they are not noticing that the sketch picked up some relations to other sketches/geometry in the model.

Does anyone have any ideas on how I can either bust or confirm this?