Stepper motor Inconsistency

[lamina]

Hi,
I am in the process of converting a Proxxon mill to a CNC machine. I have 3 stepper motors(57BYGH56-401A), a controller card, a 24v power supply and Mach 3 running on a windows XP box.
But I have a problem.
The Proxxon mill has an M5 drive which means that one rotation is 1mm. I am trying to calibrate the motors on the bench prior to fitting them to the mill. I am looking for 360 rotation and adjust the steps setting on Mach 3 until I get a decent result for a 1mm jog. Then I up the jog to say 5mm and see how close to 5 rotations I get - then adjust the steps setting until I get close to 5 rotations. Then up to 15 rotations, 25 rotations and finally 100 rotations. I can get close to +/- 5 degrees for 100 rotations. Then I can make a slight adjustment to the steps setting and all goes haywire. Suddenly I'm out about 10%. I have tried adjusting the microstepping values, the acceleration and velocity in Mach 3, a different computer, swapping stepper motors, altering the current setting on the controller board, monitoring the power supply - its always the same. About 30 minutes calibrating and then - start again. I'm beginning to lose my remaining hair. Are my stepper motors rubbish? - the controller board is based on the TB6560AHQ chip and is from China. Am I expecting too much? Before I start buying new stuff some advice would be very, very gratefully received.
Thanks.

Richard

[wildwestpat]

Hi Richard

Try following the proceedure for calibrating the axis set out in the Mach3 instructions - available on the down loads page.

The motor needs to have the lead screw as the load and be set up properly. Again follow the instructions set out in the Mach3 documentation. Set the driver microstepping to a low value as you have a very fine threaded lead screw on the Proxon. Using higher values of microstepping division cause a hughe reduction in available torque and this can cause lost steps. Also the liniarity of the microsteps is not perfect so there is not a lot to be gained in terms of precision.

As to microstepping if you have a stepper that has 200 steps per revolution then your basic movement is 1mm divided by 200 per turn so you may not need microstepping. i.e. 0.005mm per priamry step.

Mach3 download at http://www.machsupport.com/documentation.php

Hope this gets you operational - regards Pat

[lamina]

Hi Pat,
Thanks for the information.
You were spot on about using 200 steps per rotation - I have this strange desire to always use high numbers and the steppers now work a dream - apart from the x-axis which won't play ball - this is due to a faulty controller board. Maybe too many variables for me (software/hardware/computers/etc etc) but I'll keep on going :-)
One of these days I will actually make something - the mill is going to be used for making jewellery - the rate I'm going they will be ancient artefacts :-)

Richard