Strange Speed Oscillations on X and Y Axes with Timing Belts and Steppers - Need

Hi there,I have a self-built CNC www.unclephil.de/volksfr%C3%A4se-vf1/ in 850x650mm. Last week, I installed glass scales and noticed strange speed oscillations on the X and Y axes (see screenshot). Both axes use timing belts and steppers set to 6400 steps per revolution. The oscillations are particularly severe at 1000mm/min and are visible. The Z-axis, which is driven by a ball screw, does not have these issues. I have attached my configurations for reference.

  Here's what I have tested so far:

• Various settings (speeds and accelerations)
• Removed motor (runs normally)
• Tensioned timing belt
• Moved X-axis without the motor (moves easily)
• Checked all screws

Do you have any ideas on what else I could check? Or is it just the timing belt and should I switch to a ball screw?Thanks!

I think its likley to be resonance from the stepper becasue you are using direct drive and from what I can work out 64mm of travel per revolution.
I initially made the same mistake.
Ref: forum.linuxcnc.org/30-cnc-machines/31509...pinion-drive?start=0

You'll see I made a 3:1 reduction that fitted where the motor was...

Thanks for your answer. If I'm not mistaken it's 90mm travel per revolution. (71 steps per mm, 6400 steps per revolution). A Higher Value would be better in this regard, right?

I ordered Ball screw mounts and Ball screws with 5mm pitch last week actually. This would be still a direct drive. Would this setup also be prone to these problems?