Path length constraint request

Chris_Kelly

There has long been regret that Onshape does not have the capability to constrain or dimension arc lengths or path lengths like Solidworks can. It would help in many scenarios to be able to give an equal constraint to an arc length and line, or give an arc a specific dimension. Specifically, this would be helpful for complex belt paths and center-to-center distances, but I have no doubt it would come in handy in other ways.

S1mon

Arc length dimensions work just fine. Spline length is not currently possible.

https://cad.onshape.com/help/Content/sketch-tools-dimension.htm#ArcLengthDesktop

matthew_stacy

S1mon said:

Arc length dimensions work just fine. Spline length is not currently possible.

https://cad.onshape.com/help/Content/sketch-tools-dimension.htm#ArcLengthDesktop

Arc length seems to work just fine on splines.  Please see if this example meets the functional intent?  The task gets more complicated if the intent is to compound multiple sketch elements (line segments, arcs, splines, etc) together. 

S1mon

Hmm. I tried dimensioning the length of a Bézier spline and couldn’t get that to work. Perhaps it works with through point splines but not Béziers?

martin_kopplow

The important part is not only being able to dimension a full curve's or path's length, but also so use a dimensioned constraint on points on that curve. I know there are workarounds that involve creating a point on the curve via mate or a plane in 3D, but it shoud be directly possible as a driving dimension in sketches.

Chris_Kelly

Thank you! This the arc length dimension feature is certainly not well known and hard to learn by yourself. I still would like to request something similar to what Solidworks has now, where you can dimension or define a path length, which could be a set of lines and arcs that make a path, for the purpose of doing complex belt and chain runs.

S1mon

Vote here:
https://forum.onshape.com/discussion/9259/path-length-dimension

glen_dewsbury

Out of curiosity I tried the curve length dimension on some curves including a Bezier spline. Seems to work OK. I also adjusted the path length with a good result. You'll notice that at least one point n the splines is not fixed. Fixing that last point causes an error of course unless the path length is removed then reapplied as ref. I was not able to get a cumulative path length with the measure tool.

S1mon

I figured out why I couldn't get the arc length dimension to work on splines - the dimensioning process is completely different than an arc. For arcs, because a single click gives you a radius, you have to click each end point and then the curve to get arc length. For splines, you just click the spline curve itself and it gives you a path length dimension.

I've made this same mistake before. 
https://forum.onshape.com/discussion/20710/dimension-a-spline-lenght-in-a-sketch

In my defense, I would argue that the Help is incorrect/incomplete when it comes to curve length:
https://cad.onshape.com/help/Content/sketch-tools-dimension.htm#ArcLengthDesktop