Excessive micro-segments causing jerky motion on older CNC (NUM controller)

[mike_vos]

Hi all,

I'm using Fusion 360 CAM with a custom postprocessor (ccsoftcz.com, SCM/Xilog format) to generate programs for an SCM Record 220 with NUM controller.

The problem: Curves and contours are output as hundreds of tiny G1 segments (some as small as 0.07mm apart). My older NUM controller has limited look-ahead, so it decelerates at every segment -- causing severe jerking, extremely slow actual feed rates, and we've had 2 fire incidents from the tool dwelling in the material.

What I've tried:

• Tolerance set to 0.1mm -- no improvement
• Switched from 2D Contour to 3D Contour -- improves large curves but makes small curves worse

Example from G-code output:

G1 X=514.085 Y=1201.328
G1 X=514.016 Y=1201.334   ← 0.07mm difference

The postprocessor does output G2/G3 for some arcs, but most curves are still linearized.

My question: What Fusion 360 CAM settings can I adjust to reduce the number of micro-segments? Specifically for older controllers that can't handle high-density point data. I'm looking for settings like smoothing, minimum segment length, arc fitting, or alternative toolpath strategies.

I can share the Fusion file and postprocessor (.cps) if that helps.

Setup:

• Fusion 360 (latest)
• SCM Record 220 / NUM controller (year 2000)
• Material: solid hardwood (oak, douglas, larch)
• Postprocessor: ccsoftcz.com (SCM/Xilog format)

[Laurens-3DTechDraw · Accepted solution]

Hi,

Usually the arc fitting works better when the original toolpath tolerance is smaller. So set that to 0.01 or 0.005mm and the smoothing to 0.1mm for example and you'll probably see it improve. But still its going to be far from where you want it, if you explode the text I think it's already going to help you a lot, as the model will be a lot cleaner.

Video here: https://go.screenpal.com/watch/cO1065nuLEb

[mike_vos]

This worked, the only place it was still bumpy was on the ramping down when starting. The rest of the contour was good!. Thanks!