Comments on: making splines work in manufacturing

By: Amos Avery

Amos Avery — Thu, 25 Feb 2010 20:06:03 +0000

It amazes me that after all the years CAD has existed, splines are still a problem. I remember mastering the exact same technique in AutoCAD r14 when we could not drive a laser cutter to cut a splined path without thousands of tiny facets (which took an extra long time to cut). I hope Matt’s suggestion works for you as this can be a large effort that feels like a waste of time (shouldn’t our tools have grown up enough by now to be able to handle this?). Where I can help it, I’ve avoided spline curves. I agree that it would be nice if SolidWorks had a simple way to convert splines to arcs. Thanks for the refresher!

By: gale

gale — Thu, 18 Feb 2010 06:36:41 +0000

Perfect tip for reverse engineering Jason.
Thanks

By: Matt Wallace

Matt Wallace — Wed, 17 Feb 2010 18:28:20 +0000

If you are using the spline profile to drive a CNC machine tool, the faceting is caused by the toolpath tolerance in your CAM program. In Mastercam, you will have notable faceting with the toolpath tolerance set to .001 in. Setting it to .0001 will give a much better surface from the profile. I would imagine most mainstream CAM programs have a setting for this. In Mastercam, you can also set a arc filter tolerance, which can reduce the amount of code dramatically.

The problem I am betting you are running into is that most machine tool controls do lines and arcs. The spline needs to be approximated, and with a tolerance of .001, that gets a fairly long line that stays within .001, resulting in the faceting. The arc tolerance allows the CAM program to approximate sections of the spline with an arc, which is what your are doing with the above exercise, but the CAM program should be able to do a much finer job.

Or maybe I have no idea what your problem is.