Machine Cutting Out of Square

A CNC router that cuts out of square may need one of several mechanical adjustments. September 3, 2010

I have moved into a shop that has an old two head Phoenix CNC router. I am just in the process of running my first programs. I am using the machine for panel processing for our cabinets. This machine was being used by the previous owner strictly to process small wood components.

My problem is that as I cut my first large sheet it came out half an inch out of square. All dimensions were perfect, just out of square along the x axis. I am wondering before I tear into this thing, if there is typically a way to adjust the gantry for square?

Forum Responses
(CNC Forum)
From contributor G:
My CNT router used two limit switches and, using these, runs the Y motors (long axis) independently to reach a square value set in software - so that is one approach. If the machine has a homing sequence, take a close look at that (code and while it runs) and see if any adjustments are only on one side. If that isn't how your machine works, you might be able to adjust it mechanically. Maybe they didn't Loctite something that should have been. I've seen that as well.

From contributor H:
This could be for many reasons. For the age of the machine, I would think there is some play in your X axis or you can also have a backlash compensation problem for this axis that the computer isn't adjusted for. If it is a rack a pinion system, I would check to see how the pinion gear sits in the rack. Usually this can be adjusted to fix the wear. If it is a ballscrew system, you would be able to run the ballscrew by hand and feel when the table moves and then reverse the direction of turning to see how much it turns before the table moves. This is your backslash. If it is too much, the ballscrew and nut need to be replaced.

From the original questioner:
Thanks for the responses. I was able to get things squared back up. I thought I would let you know how in case anyone else comes across the same problem. The screw drives for the Y axis are sequenced together by a serpentine belt which is connected to the drive motor. I marked timing marks on the motor pulley and screw drive pulleys, and put corresponding marks on the belt. I then loosened the belt being careful to leave the left screw drive and motor marks aligned, then I was able to move the right side screw drive pulley forward a few cogs at a time. It took a few hours, but its back to perfect. Thanks again for the suggestions.