I have excessive vibration with certain speeds maybe 30-40 ipm. The vibration is loud and causes non-smooth curves - not to mention loud when jogging around. Tools vibrate off spoil board type of vibration. It's mainly on the x and y axis - but z axis has a lot as well. I am using nema 34 ( not CNCRP )

Things I have tried
- all different types of multi-step speeds (2000 - 10000)- does not seem to make a difference. I really thought it would
- added a 1/8" sheet of rubber under the aluminum extrusions - this did help a tiny bit.
- verified everything tightened
- added dampening material to metal pans holding cord guides

Things I have not tried
- loosening the belts???? Currently it is as per the directions - 1/8 in travel with fingers. Should this be looser? Does that help with vibration? Does it make the machine less accurate if you loosen the belts?

Thoughts - what does a person check through when they have issues like this?