Hello.

Im trying to change my way of milling and want to cut faster and not so deep.
But my motors are behaving strange when I try this. Specialy round objects and fillets.
Is it wrong settings, software, hardware, postprocessor or maybe just the limit of my steppers?

On the video Im changing the feedrate. Router starts to shake when it happens.
http://www.youtube.com/watch?v=dYvFHcmiJ3c

http://www.youtube.com/watch?v=XwKRRH_UHRg&NR=1
On the square cutting video, there are 4 bridges holding the part, so its cheating a little.

I can hear you motors skipping.

I will say that speed should come once repeatable accuracy has been achieved ....but that dosen't answer your question.

If you want speed do it via the mechanical aspects of the axis. Steppers are limited in how fast they can rotate and maintain torque.
Different motors can make a difference in speed, so can wiring motors differently, so can increasing the supplied voltage, increasing the Kernel speed will allow faster
pulsing to the motors if the PC  passes the driver test. So there are things you can try.
It's all a comprimise in the end.

How fast or what feed rate are you interested in?
 First look at what you want to mill and the recommended spindle speed for milling of the material.

CNC riddle of the day.  
Turtle runs around track one time and rabbit runs around manny times ...which provided the deepest mark in the dirt as they
dragged their tale?  

Surely one of the router folks will chime in with their experience.
RICH