I've got a very persistent problem with our CNC router, I won't name the manufacturer because they have worked diligently to fix the issue. This is an entry-level machine that sells for approximately $25,000. It uses simple stepper motors (no encoders or servos) and a WinCNC controller.
The machine has certain areas of the X-axis that are up to .03" out of alignment, meaning that what should be X4.000" ends up positioning at X3.970", approximately. This error occurs most noticeably in a certain range in the travel, between about X0.000" and X5.000". The error is consistent, it will come back to the same position every time. Everywhere else along the travel is within an acceptable tolerance. I flipped the rack gear end-to-end and the problem did not move.
The manufacturer replaced the rack gear, with no results. The new and old racks mesh perfectly together, so it would appear there is not a defect in the gear pitch.
The manufacturer also has rebuilt the x-axis gearbox (stepper, belt drive and pinion gear). It is currently in transit, and we should have it by next week. If that doesn't fix the issue, everybody is out of solutions.
We need to get this machine back on line, there is a ton of work piled up behind it. Thanks for any ideas.