[Aryantes]

A little bit about my machine first. Wanted to do a build thread but haven't been able to find the time yet. I hope to create a thread with the finished project sometime in the future.

Cutting Area - 48" x 30"
CNC Router Parts Nema 23 Rack and Pinion
1/2-10 5-start on Z Axis

Gecko G540 - 1909.861 steps per inch.
Super PID V2
Mach3
Hitachi M12VC
Onsrud cutters

Somewhere in my Y travel, there is a 1/32" worth of missed steps.

This happens every single time, regardless of moving in positive direction or negative direction. I have taken some pictures to help illustrate the issue.

Anything cut to the right of this point, is perfect, dead on, within 0.005".
Anything cut through this point, is always, always 1/32" smaller than supposed to be.

Its not backlash, since I can cut perfect sized shapes if I cut something small, on the 'right' hand side of the table.

I can compensate 1/32" larger if I am cutting something large and it will come out perfect size... As a result, I have to cut things in mated pairs.

If I set the machine to cut something 12", it will cut 12 - 1/32".
If I set it to cut 24", it will cut 24 - 1/32".

I've looked and looked for loose parts or something stuck in the rack but I can't find anything.

This only happens on the Y axis. The X axis is perfect.

Any ideas? Thanks.

[Mountaincraft]

Is the rack on the gantry one piece or two?

[jsheerin]

I'd agree with where mountaincraft is going - if it repeats in the same spot every time, it's very likely something mechanical, like there is a screwed up tooth on the rack for example. If you can isolate the position, look at the teeth on the rack there, maybe using a set of calipers to check the spacing between teeth, and see if there's an error in one of the teeth.

[Aryantes]

It is one piece of 54" rack.

I will see if I can measure the teeth.

I've only visually inspected it.

I agree that it is very likely to be mechanical.

I'll look closer.

[CarveOne]

I think it is likely to be a ding (or rough spot) along the edges of the steel rail, a spot of rust, or bearing preload a little too tight and the steel rail gets slightly thicker at one particular place along the rail edges. Feel the rail edges top and bottom to see if there is a noticeable change in how it feels. Back off a little on the bearing pre-loads and see if the problem goes away.

CarveOne

[Khalid]

did you find the problem?