Trim rounding error

IsleofGough

I am confused by the 1% rounding error with the trim tool in Onshape. If I create a sketch and draw two perpendicular lines, each 100 mm long and then create a pie slice by using the arc tool, everything works fine. But if I do the same with a circle instead and then trim the ends of the line and 3/4 of the circle, the dimensions shrink by about 1%. Is this to be expected?

Daniel_Kane

When I try to reproduce this on my end, these dimensions are exactly 50mm (no rounding error). Can you double-check that the lines used to trim are properly constrained? Both should have an endpoint coincident with the origin. This should result in the dimension being a driven dimension (see screenshot below).

IsleofGough

Yes, the two lines and center point are coincident but the curve to center point distance is reduced. I created a 1/4 slide but will see if a 3/4 slice is different.

bruce_williams

You may want to share the doc for the best help.  See instructs here.

tim_hess427

@IsleofGough - Another thing you might want to check, along with the lines being coincident with the center of the arc, is that the lines stay perpendicular to each other.  I've noticed, in the past, that depending on where dimensions are defined and where segments are cut/deleted, sometimes constraints are accidentally lost. 

If you retry this - make sure the lines are both coincident with the center of the arc/circle and that the lines remain perpendicular. If that's still not working, if you can make the document public and share it here, others can take it look. 

IsleofGough

Maybe the suggestion that constraints got lost is correct, as I can't seem to replicate this problem today, and I thought I did the same steps.