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Problem MadCam 4-axis, Mach3 & machine crashes??

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I am pulling my hair out trying to get 4-axis working and am asking for help from anyone who is using MadCam 4-axis with Mach3 successfully.

I am trying to mill the attached model (zip file): it is basically a squashed cylinder with a gouge scooped out of it. Madcam produces a roughing toolpath that looks correct in the viewport and in the simulator, but the Gcode produced by the Mach_3_Inch_4-axis post processor causes A axis moves that crash the cutter into the stock.

I don't know whether this is a MadCam problem, a post processor problem or a Mach3 problem, but I have painstakingly tried every combination of postprocessor options (the resulting G code files are identical regardless of whether *ANGLE_OUTPUT* is set to CONTINUOUS, ABSOLUTE, or unset), and I have tried every combination of Mach3 options Ang-Short-Rot-on-G0 and Rot-360-Rollover without success. Attached image #1 shows how the toolpath looks in Rhino and attached image #2 shows how it looks in Mach3 with Ang-Short-Rot-on-G0=OFF and Rot-360-Rollover=OFF. You can see that in Rhino the toolpaths to scoop out the the gouge are nice smooth Z-level contours, but in Mach3 the toolpaths are interrupted by 360 degree rotations of the table with the cutter below the surface of the stock. (the G gcode file produced by MadCam is also attached.)

I cut the Gcode down to find the exact cause of the crashes and discovered that during post MadCam flips the sign of A axis coordinates from positive to negative and vice versa at A=180 degrees, so that instead of a path that goes A=178, 179, 180, 181, 182... it generates a path of A=178, 179, 180, -179, -178... So any move that crosses A=180 degrees generates a 360 rotation of the table without raising the cutter to safe Z.

Can someone with a working 4-axis setup please tell me what combination of MadCam, Mach_3_Inch_4-axis post processor and Mach3 settings will result in no 360 degree "circular" rapids or feed moves below the surface of the stock with the attached model?

Thanks. I have been struggling with this for way too long.
-- Dean
(just a hobbyist trying to create some art)

Attached Thumbnails
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Name:	A axis test 3 toolpath.jpg‎
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Size:	137.5 KB
ID:	173673   Click image for larger version

Name:	A axis test 3 mach3.jpg‎
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Size:	146.3 KB
ID:	173674  
Attached Files
File Type: zip A axis test 3.zip‎ (352.5 KB)
File Type: txt A axis test 3 DEFAULT.txt‎ (216.6 KB)

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