I just finished my first 3-axis CNC about a week ago and I've noticed that all of my edges are bumpy. I've been cutting 3/4" plywood and MDF and even when cutting the depth in multiple passes the edges are still bumpy. The interesting thing is the bumps all line up in each step creating a vertical line the entire thickness of the part.

My X and Y-axis are both driven by NEMA 34 motors a with a 4:1 timing belt reduction. The timing belts are attached to shafts which drive 20 tooth #25 roller chain sprockets. I purposely used 20 tooth sprockets instead of the 9 tooth I typically see used to reduce the chordal action or deviation to less the 1%. I was hopping by doing this I wouldn’t have to worry about speed variations that, I would think, would cause exactly this issue.

I’ve changed the micro stepping from ½ to 1/8 with no change in finish. I've tried cutting from 35 IPM at .2 deep to 50 IPM at .4 deep, still same result

I’m currently using a 2 flute ¼” end mill running at 15,000 RPM.

The axes both move free and smooth.

Any help is greatly appreciated.

Thanks!