View Full Version : Laser engraving "skewing" or "drifting" and moving away from home position

Ben Arcand
01-04-2014, 11:07 AM
Hi guys,

This is my first post to the forum. I thought I'd share this fix and maybe save someone some time. I didn't find a whole lot of information on skewing/drifting and my problem was slightly different.

Ran into a problem a couple of days ago where my Epilog Helix Mini started skewing the engravings to the right as the engraving progressed. I also noticed it earlier as the home position was always slightly off between prints, but I didn't understand why at the time. It always skewed only to the right and only when it was a full-bed sized engraving. Some searching suggested a dirty encoder strip or the ribbon flex cable was to blame.

I took the x-axis cover off and I cleaned the encoder strip several times, first with distilled water, then isopropyl alcohol, then distilled water with a little dish detergent, each time testing it, each time failing to correct the problem. I also removed the optical encoder and cleaned it out, first with compressed air, then with a lint free sheet with a little isopropyl on it. Still skewing.

Skewing only occured in one direction which suggested it was missing encoder steps only in one direction. I surmised that maybe one of the ribbon cable wires had a hair crack in it that only opened when it was pulled one way. So, I tested the cable by running some current through each contact and a little LED while bending it to see if I could reproduce the problem on the bench. I didn't detect a problem, but I re-installed the cable in the reverse direction so that the other end of the cable would now be the "bendy" section. No dice, still had the problem.

An instructable suggested that soot build up could cause the belt to slip. I didn't think this was the answer, but I removed the x-axis motor and timing belt and thoroughly cleaned them anyway. Nope, not the problem.

Finally, I removed the encoder strip from x-axis (I wore latex gloves to handle it). It was attached by an aluminum plate with a dozen screws or so. It has 300 encoder lines per inch which makes it look like a grey thick "line" to the naked eye, so I inspected it under a magnifying glass. Sure enough, there was one tiny "clear" spot in the middle of the strip the size of a pinhead where the encoder lines should be. It was approximately 2/3 of the way down towards the bottom of the encoder lines.

After reinstallation of the encoder strip, everything worked perfectly. I imagine the "hole" in the encoder strip was right on the edge of detection for the encoder optics. When the belt pulled the head towards the right, it tilted the head just enough to occasionally detect the hole in the encoder lines and would drift to the right a few encoder ticks each pass. When I re-installed it, it was offset enough that the encoder optics no longer encountered it. If it happens again, I may shim the plate that holds the encoder electronics on the head so that it runs in a new section of the encoder strip (a new strip is $90 according to Epilog). In the future, I would also try shimming after cleaning and ribbon cable flipping as a way to trouble shoot the encoder.

Not sure what produced the "hole" in the encoder lines. It could have always been there. The only mechanical way I think it could happen is if the coiled grounding cable that runs under the cover bumped it somehow. This is the first time I removed cover and cleaned the encoder strip (have had the machine 1yr), so it couldn't have been from a past swabbing.

Hope this helps someone and saves them a bit of time and headache!

Dan Hintz
01-04-2014, 11:11 AM
LOL, excellent detective work, Ben. By the time I got to the middle of your prose, you had pretty much exhausted all of the things I was going to suggest. I would not have suggested looking at the encoder strip under a microscope, though if you hadn't you obviously would not have found the problem. If you see the problem rise again, I'd suggest talking to Epilog about replacing the strip. I have no idea how a pinhole could have gotten in there, either, but it still amazes me you found such an odd problem.

Ben Arcand
01-04-2014, 1:09 PM
Whoops. I guess I accidentally replied directly to Dan instead of the thread...

Thanks Dan! Yeah, if I had missed the pinhole defect, it would have driven me crazy if it started working again after putting the encoder strip back and I didn't know why it was working again.

I've got to give Epilog tech support their credit too. They did suggest replacing the encoder strip if cleaning failed. So they knew what the problem was. This way though, I saved $90, shipping time and I understand my machine even better.

Sarah Evans
02-20-2014, 1:12 PM
I wanted to thank you for posting your issue and resolution. I went into minor panic mode this morning when the same thing happened to me. Since it was a gradual slant that continued for the job but only appeared on full length jobs I wasn't sure what it could be as encoding strip issues usually look like a little jog and then a correction like the bed got wiggled while running- anyway-- you saved me some troubleshooting time. I'm hoping a thorough cleaning will solve my issue and I won't see any pinholes!