Circle Errors curve errors scatched lens

My glowforge has been struggling with circles for the past few months. See photo of earring above. This earring should be a circle.

Is there any easy fix for this problem? I also noticed a lens lid is scratched, could this be contributing to the problem?

The glowforge has been struggling with curves ever since our belt was replaced back in June 2019.

On top of that, our machine has been getting the air assist fan error. With a thorough cleaning of the fans we got it running again although it still has been failing and distorting all curved objects.

That’s most likely a belt tension issue, but could also be due to the gantry not being “straight”. There are troubleshooting steps to check and remedy both.


Not sure… but you do want to replace that scratched lens before you use the machine again. You can buy a replacement at the Shop here:

Unfortunately it looks like they are currently low on supply. I wouldn’t try to continue to use the machine with a damaged lens. (Your call, but you run the risk of increasing the damage.)

The air assist fan warning can also be triggered by strong magnets on the bed, or a printer head that is not seated correctly. Check for both of those. Again, you’ll want to get these issues resolved so they don’t cause worsening problems for you.

Good luck. :slightly_smiling_face:

I don’t see any evidence of a scratch in your pic.

I think they are referring to the small window lens - the upper left corner is very scratched.


That’s not a replaceable part. The whole machine would have to be shipped back to replace the head.

the actual lens looks like it has some abrasions as well.

and i’m still not sure why GF won’t replace just the head unit and requires the entire machine to be returned for that.

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I agree with eflyguy, first thing I would do is check that the tension between the three belts is the same. Also give the main lens a good cleaning.

Is there a tutorial how to tighten the tension of the belts?

Do you know what the small window lens does?

The rollers are mounted in a slot that allows adjustment when they are loosened. A 3mm Allen wrench is the tool to loosen/tighten the screw the roller is mounted with. When loose, apply tension to the roller with your thumb to tension the belt and hold in position until tightened.

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The belts should look like this tension wise:

and here are links showing how to adjust tension:


I’m so sorry to hear that you are still having trouble with your print results. There are several things I would like to review first.

Could you please include the following in your reply?

  1. Let us know the approximate date and time of this print? This will be helpful pinpointing it when we extract the logs from your printer.

  2. Please post a photo of the pulley under the laser arm like this example below:

  1. Another thing to check is the tension of the belt under the laser arm. Could you check the tension of your belts for me?

When pressing lightly on one side of the belt, the other side should not move.

Like this:

(You should see an animated image above)

Please let us know in your post if you find anything out of place. We will take a look at the photo and follow up with more details.

That .gif isn’t showing - try this :slight_smile:

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That print was done on sunday 12/15 during the afternoon. The tension for the belt under the laser arm is actually pretty loose. I’m not home right now to take a picture. The other side of the belt moves when I press lightly on one side.

Thank you for letting us know. It does sound like the belt is loose and needs to be adjusted.

I would recommend tightening the belt as a next troubleshooting step. For these instructions you will need a 3mm hex key.

  1. Turn off your Glowforge.
  2. Carefully remove the crumb tray.
  3. Without removing the carriage plate and belt, locate the black pulley fastened by a metal screw on the right end of the laser arm.
  4. Insert the short side of the 3mm hex L-key into the metal screw with the long handle pointing toward the front of the unit.

  5. Turn the key clockwise to loosen the screw until the pulley can slide with some friction. Don’t remove the key from the screw.
  6. Holding the key with your right hand, use your left index finger to push the pulley to the right until the belt is taugh. Don’t stretch the belt or touch the belt with your fingers as this can affect the tension on the belt.
  7. Applying firm pressure with your left index finger, turn the key counterclockwise to tighten the screw. Make sure the pulley doesn’t move during this time.
  8. Continue tightening the screw until you can’t turn the key anymore.
  9. Gently slide the carriage plate from side to side to ensure it moves smoothly and the belt does not catch or sag.
  10. If you’re not satisfied with the tension on the belt (it should be taut, but the belt shouldn’t be stretched), go back to step 4 and try again.
  11. Once the tension seems nice and snug, try a test print and let us know if you see improvement in the results.

If you have any questions or run into trouble along the way, don’t hesitate to reach out! I’m happy to help.

It has been a while since we have heard from you here, so I’m going to close this thread.

If you are still running into trouble, please start a new thread or reach out at