On the Original Prusa XL, adjusting the belt to the optimal tension is crucial to achieving good quality on the prints. A loose belt can cause Layer shifting, Ghosting, or other print abnormalities, like getting an irregular shape instead of a perfect circle. An over-tightened belt can cause an irregular movement in the X and Y axes.
The Original Prusa XL geometry is CoreXY: it has two belts for the XY-axes.
Alignment
It is crucial to have perfect alignment between the right and left sides. The X-axis should reach both sides of the front printed parts at the same time.
For the procedure, ensure the stepper motors are disabled. This can be done by switching the printer off, or through the LCD Menu -> Control -> Disable Motors.
By hand, move the toolchanger or Nextruder to the frontmost Y-axis position, and to the center of the X-axis.
Test the alignment by squeezing the CoreXY gantry and the corner printed part, first on one side and then on the other. There should be no play between the parts. With perfect alignment, the squeezing test on both sides feels like pressing two solid objects together.
If there is misalignment, then the squeezing test reveals play in the front corner. In that case, loosen the belt on both sides slightly until the gantry is aligned. Loosen the tensioning screw of the corner with more play less than the other.
Repeat the procedure and squeezing tests until perfect alignment is achieved.
The right side image shows the mechanism behind the tensioning screw. Tightening the screw pulls the tensioner towards the front, resulting in a more tensioned belt on that side.
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Belt tuner
We have our own belt tuner. The application determines the belt tension by measuring the frequency of the vibration generated by strumming it. Follow the instructions in the video below to adjust the belt.
Homing tower
We prepared a specific homing tower, to visualize possible issues with the belt tension and have the possibility to correct them on the spot.
In case the belt is loose, the tower will have an inconsistent finish, with scattered material on the walls instead of a smooth finish. Without interrupting the print, tighten the screws on both Y-axis rails by half turn.
If the print finish does not fully improve, repeat the procedure once again, until the homing tower has a smooth, consistent finish.
An over-tightened belt can result in layer shifting.
Once the tower has a smooth finish, loosen the same screws very slightly, and observe if this further improves the tower. Repeat the procedure until the tower has an ideal finish.
31 comments
- I see in the video, the tool changer is attached to the carriage. But the demo printer is a one tool model. I have the 5TH, so I didn't have the tool changer on the gantry. Does that make a difference? I don't know. I am currently printing a homing tower as I type my experience. We'll see how it comes out.
- So first, follow the steps with the carriage all the way to the left side. The video is unclear on where exactly you should have the XY carriage stationed. I stationed right behind the 12th screw, which as per the video, the XY carriage aligned with the very back of the Z axis bearing housing.
- Strum on to get about 80 Hz on the right belt, then repeat the process on the left to get similar tension
- Now, move the XY gantry to the front, and move the carriage as much to the middle of the XY gantry and try and be as precise as possible. Now, check for play between the two. REMEMBER, you're trying to BALANCE out the tension between the belts, which run the whole length of the core XY. So loosen the tension screw on the side with no play and make the SAME tightening of the screw on the side with play. For example, if you loosen 1/2 turn on one side, tighten 1/2 turn on the other.
- It helped me to do little by little. I didn't go more than 1/2 turn at a time.
- Then repeat the process of the strumming while trying to keep the location of the gantry and location of strumming as consistent as possible.
Just keep going back and forth until they are both balanced and there is no give. It took me repeating the process 4 times before I got both equal tension via strumming using the PRUSA app, and no play in the front tensioner.
I hope this helps you guys. I'm very interested to hear how it goes with you all. Good luck!
Edit: Someone made a comment below to remove the spools off the holder, since it can vibrate. So true, especially if filament is loosely wound.
Also, my phone doesn't hear the frequency at all. I had to put the bottom edge of the phone onto the printer arm above the belt, blocking the microphone, but enabling the microphone to physically "feel" with the vibration. It's still not consistent but does occasionally give a reading.
Finally, I bought the Belter tool to have a more reasonable way to measure the belt tension in the future. The wierd thing is if I set both belts to the same tension it pulls the gantry out of alignment. If I use frequency to get them the same and aligned, the Belter gives different readings per belt. Very strange and not intuitive. For anyone curious and wanting to compare readings, my belts are at 78-80Hz, gantry is aligned, and Belter reads 7-7.05 on the left belt and 7.2-7.25 on the right belt. This is with the printed end piece on the Belter.
Interesting on the readings between the left and right. I will try to share my settings when done.
I have -6.25 on the left at 82Hz and -6.24 on the right at 81Hz