Machine:
Torchmate Small Shop Machine, 4x4, ~2007 original purchase
501A(?) USB Signal Generator
3A stepper motors (didn't think to write down the PNs)
2.25hp DeWalt Router
1/4in solid carbide router bit
Torchmate 3 Driver Software (Torchmate's website is down, and I'm at work, so I can't double-check this!)
BobCAD/CAM V21 gCode generation, Torchmate w/ FlashCut Post-Processor
Computer: Windows 7 64bit (w/ 64bit 501A driver)


I have a Torchmate Small Shop machine 4x4 table I just setup and am using as a CNC router. As of now I have successfully cut circles with good interpolation (i.e. they turned out consistently round and of the proper dimensions) and a few polygon profiles, both with no issues.

My problem is that when I program the machine to cut a rectangle with fillets on the corners the drive 'jumps' or 'stutters' or 'jerks' right at the transition from cutting a straight line to an arc.

I tried reducing feed rates down to 10ipm, reducing drive accelerations down to 2ips^2, turned the feedrate up to 12ipm (above the starting feedrate of 11.75ipm), I checked the X, Y, and Z drives for any loose drive components (belts, gears, etc) or backlash and fixed a few things, but they didn't solve my problem. The only adjustment that sort-of masked the problem was changing the maximum arc feedrate down to 1ipm, I experimented with it set to 10ipm and 70ipm (default).

The problem was reproducible with no cutting forces on the router, I ran it 'in air' and still saw the stutter/jump/jerk.

Any thoughts on what to try next? Any help would be greatly appreciated.

Edit: I think I should add that the cuts are still turning out very repeatably. Its not missing any steps that I can detect after multiple passes on the same profile, even under cutting loads.