I'm stilll pondering about this. I would have though mechanical binding would cuase a less repeatable error. Maybe there is some damage to the rack in that location? a damaged tooth? some swarf/grit in the rack? just thoughts....

Are all the other letters perfectly smooth or do they all exhibit a little of this stepping?

Quite a few letters do exhibit some stepping,
The rack is clean and lubricated as well as the linear bearing guides, though for some reason the drives sound "rough" in that general location!

The photos show stepping on the Letter H i think, So it is happening over the sign area.

is the machine cutting speed fast? i had a similar problem with diagonal cuts with plasma at speeds over 240 ipm.the diagonal cuts were wavy .

Hi Tripleback,
No we have slowed the cutting speed down to like 8% of the programmed 40mm/sec,
I've always been worried about the momentum of the gantry causing the waves, but it's moving REALLY slow!

What kind of motion control are you using? Can't see much info in your .xml file. I figure you're not using the parallel port? And i can't see any of you Stepper, Velocity or acceleration values....

Quite a few letters do exhibit some stepping,
The rack is clean and lubricated as well as the linear bearing guides, though for some reason the drives sound "rough" in that general location!

I'll throw my 2c in here. It looks like a mechanical problem to me - stick-slip motion. Especially with your comment about sounding rough.
There may also be a structural rigidity problem on top of that. It 'jumps'.

Cheers