problem with the X ais

[ennech]

Hi, its my first post although I have been using Mach 3 for a little time.

I have converted a Chinese round column mill/drill to CNC operation using NEMA 23 steppers (3.1NM torque).  I have encountered a problem with the X ais which I would be appreciative if someone could point the way to a solution.
I tried milling a 75 mm square with rounded corners by successively increasing the depth of cut.
It soon became apparent that the X axis position crept nearly 1 mm in the +ve.  direction with each successive cut, the size of the square remained reasonably constant.  The Y axis also kept position ok.
This indicated to me that the travel in the negative direction was less than the positive direction.
I then may a large number of measurements  to the x axis (cutting fresh air) using a range of feed speeds and accelerations these indicated that the positive travel was indeed greater than the negative travel.  I also tried varying the number of micro steps from 2 to 125 without any improvement.  Needless to say I eliminated any backlash as I reversed the travel by making a small initial movement  in the direction of travel before zeroing.  I also tightened and loosened the x axis jibs without it making much difference.
Below is a list of x-axis  measured travels.  The speed was 300mm per min. and acceleration of 50, the microsteps for this exercise was 10.

Mach 3 X reading mm         +ve travel mm         -ve travel mm
50.00               49.96            49.51
10.00               9.84            9.82
10.00               9.90            9.69
10.00               9.96            9.72
5.00               5.03            4.90
5.00               4.88            4.89
15.00               14.97            14.71
15.00               14.71            14.69
20.00               19.78            19.36
20.00               19.94            19.36
2.00               1.98            1.85

[Tweakie.CNC]

Hi Ennech,

Choose a value for microsteps that your machine runs smoothly with then, within motor tuning, set the steps per unit accordingly and adjust the velocity and acceleration to suit. Once this has been done there is no need to adjust microsteps again unless you think that you can improve machine performance over your earlier setting up.
Check all your wiring for poor connection, especially the axis you are having trouble with and also check the mechanicals such as loose coupler between stepper and leadscrew (check all grubscrews for tightness) etc. etc.
I know you have probably already done all this but most problems turn out to be something real simple that has just been overlooked.

Hope this helps,

Tweakie.

[kf2qd]

Check for any mechanical problems with X. Is it binding when moving in one direction skipping steps? Is something slipping when going in the one direction? Make sure you have no mechanical problems FIRST. Only then can you make any changes in the settings. Does it work at a slower speed? I would assume that both axis have the same hardware, but are they both configured the same on the drives (check the configuration switches)?