Found a thumping when my machine is cutting or scoring!

I was trying to make a craps table layout to practice again and while cutting it out a notice a loud thumping while the machine is making moves to new start points. watched it for a bit and noticed that it was from the belts jumping across the teeth of the g2t pulleys. I have a new assembly for the head that has a belt but I am in need of 2 for the main gantry. I would like to find some from somewhere like gates so I was hoping to know the length if those 2 closed loop belts. otherwise I was hoping to just get 2 replacements for these as I fear they are stretched.

I’m not sure about the gantry belts but the carriage belt is a strip, not closed loop. I think the gantry belts are the same.

The ends are clamped under an aluminum block that has grooves that match the belt teeth. The first time I removed the carriage I disconnected the belt.
I was glad to see the dust on the belt marked exactly where it had been clamped so I could reassemble the belt to the same length under the clamp.

It seems odd the belts would have stretched, they are very strong and fiber reenforced. I have a lot of time on this machine and there is not a hint of stretching. Maybe the belt clamp is loose and the belt slipped.

Another possibility is that the belt pulley slipped, they are adjustable. You can see they are mounted in an adjustable slot on the rail. The tool to tighten/loosen them is a 3mm Allen.

I would wait to hear from support for an official answer,
but it seems to me more likely a pulley or a clamp has slipped.


I’m so sorry for the trouble, and the delayed response.

I can find some replacement y-axis belts if yours are damaged, but I agree with @PrintToLaser it may just need to have the tension adjusted.

I found some instructions to fully replace the belt (copied below). I know it’s not exactly the same, but you may find them useful reference to you adjust the tension. In the second section called “Installing the new clamp and belt”, steps 5 and 6 include photos of the pulley that needs to be adjusted.


  1. Remove the belt (just from the stepper, no need to remove it from the laser arm)
  2. Loosen the screw, adjust the pulley, tighten the screw.
  3. Put the belt back on
  4. Test
  5. Repeat as-needed

Can you give that a try and let us know if that works?
Or if you do need replacements, let me know, and I’ll track them down for you.

Here are the (full replacement) instructions:

Removing the old clamp and belt

  1. Turn off your Glowforge.

  2. Open the front door and carefully remove the crumb tray.

  3. Underneath the laser arm on the right side, you will see two small screws. Using the tool we provided, remove both screws to free the belt clamp.

  4. Using both hands, gently slide the laser arm towards the front of your Glowforge to reveal the belt clamp.

  5. Slide the laser arm back towards the center and unhook the belt from the motor on the front side of the unit.

Installing the new clamp and belt

  1. Grasp the belt by the clamp and pull the rest of the belt through the laser arm towards the back of the unit to remove it.

  2. Pick up the new part so that the clamp is in the center of the belt. Make sure the holes in the clamp are facing you and the screw is at the top.

  3. Thread the right side of the belt from the back of the laser arm to the front of the laser arm as shown in the first photo below. Make sure to insert the belt between the holes on the top and the metal part on the bottom of the laser arm as shown in the second photo below.

  4. Loop the front side of the belt around the motor.

  5. Using your left hand, grasp the far end of the belt and set it on the bottom back half of the pulley. Use your index and middle finger to hold it in place. The belt will not be fully on the motor.

  6. Still holding the belt firmly in place with your left hand, use your right hand to gradually pull the top portion of the belt towards you. The belt should roll onto the pulley until it is secure.

  7. Push the laser arm back so the clamp is hidden behind the plate that holds the laser arm to the rails.

  8. Line up the holes in the plate with the holes in the clamp. You may have to pull the belt up a little, as shown in the photo below, to get them aligned correctly. You can check to see that the clamp and plate are lined up by inserting the tool into the holes and ensuring that it goes through both parts.

  9. Replace the screws using the tool. There you have it! Your Glowforge is good as new.


It’s been a little while since I’ve seen any replies on this thread so I’m going to close it. If you still need help with this please either start a new thread or email