I keep getting the Print Stopped Material Thickness Error

So, I have been using my glowforge for years now. We were part of the crowd funding.
Had to only get one replaced…

I have had this problem once before and it resolved itself.
I don’t know why I can’t get this one to do that.
I am trying to lightly etch on some designs on stretched canvas so my kids can paint on them. I have taken out the crumb tray and put the canvas in there - like I have done innumerable times before with various projects.
I had the material thickness error and restarted my GF and the GF browser window and got it to run.
I put a second canvas in the GF and hit Print on the web page without changing any settings. NOPE - got the error again.

  • Restarted everything - Error
  • Restarted in different orders - Error
  • Turned off unit and moved the head under the GF symbol, turned it on and - ERROR
  • I searched the community boards and cleaned the lenses and the depth finder windows on the bottom of the head. I checked the pins and connections - everything is tight. Started it all up and - ERROR.

Am I missing anything?
Please help!

There is nothing obvious to do in my opinion except the things you have done. If this was happening to me I would go all the way back to the beginning. Put the honeycomb tray back in with nothing on it. Turn the machine off and back on. Put a piece of 1/8" material in, use the set focus tool and see if the Gift of Good Measure would run. If it did I would breath a big sigh of relief and try the canvas project again. I would use the set focus tool. If the Gift of Good Measure didn’t print I would contact Glowforge support.


The focus process cannot be bypassed even if you manually enter a material’s thickness. It shines a red laser from one side of the main lens, which is detected by a camera on the other side. Regardless of whether you enter a manual thickness, or use the ‘set focus’ feature, if it falls out of range, you will get this error.

Unfortunately there is no way to bypass this step, and if the inside of the windows (on either side of the main lens opening) get contaminated, there is no simple way to clean them. It can be done, but is not a task for the average user.

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Thanks for the response!
I did just that - put the crumb tray in and ran a cut/engrave on a proofgrade plywood and it went just fine.
After that run, I took the crumb tray out and put the canvas in with the supports and set it up - error again!
It’s only measures at a .09in
I even shaded the area with a pencil that the GF red light measure instrument hits, thinking it wasn’t picking it up because it was a white canvas…
It works on the proofgrade - just can’t figure out why it won’t work on the canvas.

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Try lifting the canvas higher off of the floor of the Glowforge. Try putting a colored piece of paper on top of the canvas and see if it throws the error.

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The GF uses “parallax” to determine distance to the workpiece. The measurement beam (a plain old visible red light laser diode) shines at a slight angle relative to the horizontal plane described by the gantry motion/top of the crumb tray. The camera sees the light, and the position of the spot will vary in direct proportion to the distance between the laser diode and the reflecting surface.

If you put two different materials of the same height in the machine and one works and the other returns a thickness error, the only explanation I can think of is that the camera isn’t seeing enough of the red laser spot being reflected. Canvas has a very coarse irregular surface and it may not reflect enough of the light to satisfy the camera. Worked before, because that was a different batch of canvas.

The “albedo” of the surface matters. But the “specularity” probably does, too. A surface that returns a fuzzy reflection is probably going to present more problems for the camera than a surface with a sharp reflection.

I’d mask it and see if that fixes the problem. Or shoot the canvas with a light coat of white paint. Neither may be practical for what you want to actually do, but either would conclusively prove or disprove my theory…


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