Cutting Polycarbonate Profiles, Help!

[Kberry]

Hi all,

I am attempting to cut 2D profiles from 0.25" Polycarbonate sheet. We are getting a chattery edge on all radius as well as entry/exit points. I am using a Shopbot Buddy and an Onsrud 66-087 single O-flute Edge Rounding cutter at 100ipm and 15,000rpm.

We are getting great results in the straightaways but the curves are bumpy and the entry and exit point is very chattery. I think by extending our entry/exit lengths and radius I can fix that problem, but what settings do I need to alter to get a more consistent finish in the curves?
I read thru the forums and tried altering the ramp settings but there was no change in our edge quality.

Thanks in advance

Keith
IDS
Venice, CA

[Gary Campbell]

Keith...
Did you save the file using the "arcs" postP?
Which program did you create the vectors with?

[Kberry]

Gary,

We use Rhino with RhinoCAM and export to the Shopbot. Postprocessor is Shopbot, not the ShopbotGcode.

[Gary Campbell]

Keith...

It is pretty likely that your design uses short line segments instead of arcs for radius vectors.
You may want to export vectors to one of the CAD/CAM apps and post using the "arcs" post. It uses gCode arcs and results in much nicer radius cuts.

[joe]

Keith,

I think Gary is correct. This has been a problem with SB. Circles and curves which are made from short links seldom cut smoothly. Also Polycarbonate shows every defect. I'm cutting letters from this material which is .75" thick using a V bit. It's a test of nerves since it doesn't sand very well.

Joe

[Kberry]

Hey thanks guys,
I tried to create a Gcode file but it was turning off our spindle when I started the file, any suggestions I dont really understand the coding aspect that well.

Also our machine is really new, is there any sort of "breaking in" time, where we need to go back and readjust our motors, track etc?

[Kberry]

Here are some photos of our recent profiles you can clearly see that pattern bump/ridge

[jerry_stanek]

I would try a rough cut with a straight cutter with an offset then the finish cut so you would only be taking off a small amount and putting the bull nose in.

[Kberry]

Ok I ran a Gcode file, *.gcc and got the Same Problem. This leads me to believe it is the ramping in the Shopbot controls, any suggestions?

I also tried a straight cutter roughing and the bullnose only taking .020" and still no luck.

[Kberry]

Is this correct for Gcode? I had to delete M03 as a command because it was turning off our spindle.

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