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General Mach Discussion / Very green newb, Is this possible?

« on: August 31, 2009, 09:56:14 AM »

I am very new to cnc, and have recently built a Phlatprinter MKII from phlatboyz.com  I am using a Mechatronics bi polar 3 axis micro step motor driver, with 3 nema-23 stepper motors.  The machine is all belt driven.  The x axis is a large belt driven roller similar to that of a large format printer.  Y and Z are on a gantry below the cutting surface, and the cutting bit protrudes from below.  When I run a cut file X and Y do not finish where they start.  Y drifts progressively farther and farther in the + direction, and Z does so as well.  To help diagnose the problem I rewired coil 1 to coil 2, and coil 2 to coil 1 reversing the steppers, then in mach I reversed settings so everything ran in the right directions again.  After reversing the steppers I still have the drift but in the opposite directions.  The drift is very consistant.  The same cut file ran over and over leaves the cutter the same distance off.  I have tried lowering the feed rates and acceleration, with no changes in the drift.

Is it possible that one coil is working better than the other in the steppers?  If I could set steps per unit in the + direction, and then in the - direction independantly couldn't I compensate for this drift?

Jeff