K40 left-right motion jerky

[TimMasters]

Hi all. I just bought a 40-watt Chinese laser and am setting it up. It arrived in apparently great condition, with nothing obviously broken, bent, or missing. The laser tube works, and the software seems to have installed correctly.

But when I manually slide the head left or right, it runs smoothly for several inches, then snaps hard into a fixed spot. With some effort I can slide it smoothly and easily a few more inches, then it snaps again. This happens every few inches, across the entire extent of the range. It is as if there are a few strongly preferred positions equally spaced a few inches apart, with the head strongly gravitating to those discrete spots. The gravitation is so strong that the stepper motor cannot move it out of one to home it. If it is manually slid to the left of the leftmost snapping spot, it homes correctly. And everything is smooth and well working in the front-back direction. Any thoughts? Please???

[Jim Dawson]

If it's a rack & pinion drive, look for crud in the gears, or maybe screws not countersunk properly or not deburred well.

[wmgeorge]

Its notched belt drive check for cr@p in either the pulleys or belts and binding on the rail surfaces, or bearings if it has any.

[TimMasters]

Oh sigh, I found the problem and it is likely not repairable without replacement parts. The laser head fastens to the rail with four bearings, one on each corner. I made a pencil mark on one of the bearings and I see that the jerky stop place is at exactly the same rotation point. So I guess at least one of the four bearings has a flat spot or some such thing. Everything is perfectly clean, and the bearings look totally sealed, so there is nothing to clean. Maybe the machine sat a long time in one position and something got flat. Is that even possible??? But I see no other possibility. But I can't imagine how little bearings like that could get a flat spot.

[jfong]

Lightobjects.com sells the replacement white bearing rollers and most parts for the k40