Offset curve in a sketch misbehaving

Dean_Gardner

Has anybody recently had a sketch fall over due to an offset curve inside the sketch go bad?  I have recently had an error manifest itself through derived bodies because my original sketch constraints had failed.  Basically I cannot move the vertices even though they are not fully defined. Trying to recreate what i originally had cannot be done, nor can rolling up the tree to recreate the sketch.  I try it on the same imported file and it does it no problem. Just wondered whether anybody had seem and dealt with something similar with their work.  Worked in mid august, problem happened in September. Support ticket has been raised.

S1mon

Offsets are not that stable as the inputs get more complex. Part of the problem is that there is no clean mathematical exact solution for offsetting a curve unless it is something simple like an arc or line. Offsets of splines are always an approximation of degree-3.

If you really need something to be more stable, a trick that I've often used is to extrude a temporary surface and offset the surface. Surface offsets are less brittle than what happens in the sketcher.

Other tricks are to avoid having a lot of entities in the sketch and especially things that are tangent or curvature constraints to an offset. 

Dean_Gardner

Thanks @S1mon - useful and makes sense.  Shame that it has broken on its own accord - though i suspect there's a reason at large which will likely be my fault..!