maybe someone can answer this question.
 when I cut a round profile on my cnc router
and am going slow 150 ipm the servo motor is turning
at 46 rpm ( direct pinion drive to rack )
I get jagget cuts on diagonal and radius.
looks like a zix zag cut.

So I run same program use mach to increase
cutting speed to over 300 ipm  servo motor turns at
about 90 rpm  the jitter is almost goes away.

I thought it was the signal to the motors being slow.
If I speed it up and the movement gets smoother
So It cant be the slow signal. 
Am I right?

What is going on?
Thanks,
Bob

mach 3
ess
direct drive rack and pinion