spline filtering

[mechman01]

hello all, i use contours and curve5s to cut 3d splines that define molded plastic part edges on a vacuum fixture. i use 5 axis thermwood routers. some of these NURBS splines can be quite complex thus giving me a very jumpy toolpath sometimes. i have tried to filter in different ways and it does not produce a smooth toolpath. for the curve5s i play around with the curve following method-->chord height to "smooth" out my splines and it works but not to well. i have also tried cnv to arcs with no success.

 

so basically my question is:

 

what is the best way to smooth/filter 3d splines, that have control points that are spread out in one area and clumped in others, thus producing jumpy toolpaths?

[P_Scott]

mechman01,

 

Welcome to the forum. I'll try to be of help on this. Mastercam uses "linearization" and "depth variance" tolerances to help break up 3D spline and surface data into tiny linear moves. Using the Filter settings, you can usually replace the tiny lines with arcs. I tend to make my Filter tolerance about twice the size of the linearization tolerance, or generally a 2:1 filter ratio. I also try to look ahead by as many entities as possible (say 1000 instead of 100). You can Search this forum on other topics that have discussed Filtering.

If you want to break up the spline data first, I suggest trying the "Modify-Break-Spl to arcs" function. It usually works better than the "Cnv to arcs" function from the Modify menu. You may discover that there is more than one way to accomplish what you are attempting to do with Mastercam. That's part of the beauty of such a flexible application. You could also upload a file in question to the forum FTP or e-mail it to me directly if you would like some more specific advice. HTH

[MATT Q]

Hi Mechman01,

I program a lot of thermoformed parts using curve5 paths and contour paths. When I have a choppy spline I recreate it with automatic splines and make sure they are nurb spline for some reason parametric splines seem to give it a lot of trouble(switching sides and doing some strange things). Then I run it through metacut to filter it. When I make the splines I make them large so they don't have a bunch of tiny entities in there. That seems to help also.

hope it helps

[ak762]

Hi Peter Scott,

 

At ones I tried to repeat step as you mention (say instead of 100).

Will be interesting to know how you see that look ahead1000 help you

 

But when I open mill9m.cgf I see

926. Default toolpath filter look ahead (<=100)? 100

 

Will be interesting to hear opinion from CNC guys is it possible to help?

[dgriffiths]

mechman01,

 

I also program many 5axis curve programs to thermwood routers and have encountered the same problems with 3d splines. Have you tried using a G09F8 in your code. This is a tangency factor that helps smooth machine motion when cutting splines. Increasing the look ahead to 1000 is also helpful. Hope this helps.

[mechman01]

dgriffeths,

 

I usually use G09F10. Have you found F8 to work better?

[dgriffiths]

mechman01,

 

I have tried F10 and F12 on a few programs and F8 still seems to work out the best for me. Also, there are times when I have had to manually program 3D-arcs (G72 G73) to smooth the toolpath. Unfortunately this is not always an option. Good Luck.