Hi all,

I am trying to tune a gantry that is running on rack and pinion system under no load. I have identical motors, racks, and pinions on both sides. The A axis is slaved in mach to the x, and both motors are using the same steps per inch in mach. However, when I run the length of the table, I am off by a huge amount - about 3/8 of an inch -- one is too far, and the other not far enough. If I run even 5 inches and return, it is off almost the same amount -- . basically, the gantry skews as much as the hardware will allow it to. I am pretty certain from visuals and noise that the steps per inch is off on one or both motors, they thus bind, pull out of true, and start losing steps...

Since they are slaved and there is no way to run one motor without the other, how can I test the tpi and set it, or what else can I possibly do? In theory they should both have the same steps per inch, so I don't really understand the issues here. They "should" be at 200 steps per inch, but in fact they are set at 170 since that is what I measured using the mach tuning function (I am not using micro-stepping, since I am attempting to build something fast with like .2mm accuracy as ok for now).

Thanks in advance!