new to cnc... what am I doing wrong?

I have built a 3 axis router with the following:
3 nema 23 motors bi-polar
xy drive automation driver and breakout boards( xd-8 & xd-14)
Ubunto 10.04 LTS
EMC2 cnc software
The drives say:
step time 1uS
step space 1uS
direction hold 200 nS
direction setup 200nS

For the life of me I cant get it to make a circle.. it comes out an elipse. I also fine that begining and end don't meet when they should. Anybody help me with this I would be really happy...

Thanks

mtofire

I'm a CNC newbie as well with zero actual machining experience however I do remember reading about a similar issue. I believe that it was tracked down to a problem with the anti-backlash nut. I'd suggest watching your anti-backlash nut as you run a jogging test to see if any slippage is noticed when the axis screw reverses direction. It seems that having the anti-backlash nut being either too loose and causing slippage or too tight and causing excessive binding may both affect the accuracy of the cut.

Anyway, hope this helps point you in the right direction.

most incorrect problems relating to circles not being correct , is mostly down to either timing issues missing steps and or mechanical backlash or binding , so let me expand further

one problem is missing or incorrect steps due to either stepper tuning or even binding causing the motor to effecively stall , make sure the screw and nuts are smooth to turn
over the full length and if your using threaded rod their are no bent rods , one trick is to run a die down the thread to clean any rough edges , stainless threaded rod is better then mild steel ones
for keeping smooth .

also stepper motors loose torque the faster they run , so while configuring keep the microstepping lower will help , this may mean changing settings in your controller to start with
once everything is running , then fine tune everything , using microstepping on systems at say 8 or 16x is just no good on router diy systems and in most cases mechanical build tolerances only make matters worse


as JacKnife suggests check your mechanical issues such as Backlash .

one or a combination of all the above will cause ellipses