Circle cuts vary in size 20 mil along x axis

[KT88saturate]

I have a commercial 2'x4' cnc with rack and pinion drive on X & Y. The machine cuts about 20 mil over size on the far side of the x axis whether its a 3" rectangle or 6" circle. Its close to spot on near x0. The pinion doesn't show wear and is tight against the rack. I've made sure the rack is straight with a straight edge. Checking the x axis resolution shows that it is spot on. Y axis doesn't appear to have this issue. Belt is tight.


I've been cutting mdf for testing this with 1/4" bit, 1/8" DOC, just 50ipm feed at 12k rpm.

What is possibly the issue? Some weird electronics problem?

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[CNCMAN172]

Check your stepper motor could be dragging or missing steps

[KT88saturate]

Check your stepper motor could be dragging or missing steps

I was hoping it would be as simple or easy as that but the error is positive and consistent with any feed speed. I am cutting at 50ipm at 1/8" DoC with a 2" length 1/4" bit. Cuts on the right side of the table are always ~20 mil larger than the left.

[CNCMAN172]

Try to use a pencil in spindle and have it draw a circle without turning on the motor, just unplug power to VFD. This will let you know if you are getting EMI interference. If the pencil circle are perfect you have a noise issue

[KT88saturate]

Camaster said they would have to send someone out but its a two month wait. Twisted gantry.

WTH causes a twisted gantry?

[CNCMAN172]

Camaster said they would have to send someone out but its a two month wait. Twisted gantry.

WTH causes a twisted gantry?

This could happen if you have two motors driving the Y axis, one on each side. If they get out of sync one motor can put too much force, but depending on the construction it would be hard to twist a strong gantry.

Russ