Calibration issues.

[Pulcik]

That is a lot.
It seems it is load related.
Try to make a square in some harder material than wood. Aluminium, plastic, green sikablock. And clamp it well.
There might be two outcomes from it. If it is spot on, it is the was the issue of clamping or material itself. If it is even more than in wood, it is lays between deflection and motors (skipping steps, or slipping couplers). If it is servo motor, than it is tuned incorrectly.

[johanbhi]

It sounds like you've put in a lot of effort to calibrate your CNC machine after switching to UCCNC. Kudos to you for being thorough! However, it can be frustrating when the X axis doesn't align perfectly despite multiple calibration attempts.

Based on your description, it seems like you've taken the necessary steps, such as setting up a scale on a batten and marking it accurately at 1200mm. You've also checked your drawing and tool settings, which eliminates some potential sources of error.

One thing that caught my attention is the discrepancy you mentioned in the DRO reading after moving the X axis 1200mm with the Calibration glass tool. The difference of 0.0034mm might not seem significant, but it could contribute to the slight under-cutting you're experiencing.

To address this issue, I recommend checking a few additional factors. First, ensure that there are no mechanical issues with the machine, such as loose belts or excessive play in the X axis. Even small inconsistencies can affect the accuracy of the cuts.