Every once in a while you run into something that you couldn’t foresee having problems with. We ran into this over the past couple of days.
The Problem
When trying to machine a profile that has a spline in it, we would end up with a jagged surface that was not desirable for our end product. If you can imagine, it looked like a bunch of tiny flats that flow into each other to give you your splined surface. We wanted an end condition of a nice smooth surface.
The Solution
After some research and testing, it was determined that spline sketch entities were the cause of this problem. I was hoping that SolidWorks offered some sort of a spline to arc conversion but could not find anything so this is the solution that we came up with.
1.) Start with your original sketch with the spline sketch entities in it.
2.) Select your spline sketch entity > go to Insert > Reference Geometry > Point. Select the last option which is “Along curve distance or multiple reference points” and then select the last radio button which is “Evenly Distribute”. Now enter in the number of points you would like to space evenly along your spline. The higher the number the more accurate your end result will match the spline.
3.) Start a new sketch on the same plane as your original > select all of the entities in your original sketch but DO NOT select the spline sketch entity.
4.) Hide your original sketch and do multiple 3 point arcs between the points. For example, Point 1 to Point 3 with a center selection of Point 2.
5.) Delete any tangent relations that are automatically added.
6.) Repeat step 4 until your sketch is fully closed by adding all of your 3 point arcs.
Your end result should look similar to the picture below.
Now you have a profile that you will be able to work with and also but able to machine into a nice clean surface. One thing to remember is that the more points you add to the spline, the closer your 3 point arcs will match the original spline profile.
I hope that all of that made sense, if you have any questions or having another way of doing this feel free to drop me a comment. Eventually I hope would hope that SolidWorks would find a way to automate this process as it seems that I am not the only one that has run into this after scouring the SolidWorks Forums the past couple of days for a solution.
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.
Perfect tip for reverse engineering Jason.
Thanks
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!