On the Prusa CORE One, 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.
Alignment
Before adjusting the belt, ensure the proper alignment of the CoreXY structure.
- 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 Nextruder to the frontmost Y-axis position, and to the center of the X-axis.
- Press the gantry corner against the front of the CoreXY, and make sure there is no play. Do this procedure on both sides. If there is any play in either side, perfect alignment is not achieved yet.
- Slightly loosen both the belt tensioner bolts. Loosen the bolt on the corner with play less than the other.
- Repeat steps 3 and 4 until a perfect alignment is reached. Do not worry if the belt is loose at this stage, adjusting the belt tension is done at a later step.
Belt tuner
We have our own belt tuner, incorporated in our Prusa App, or available on our belt tuner webpage.
In the meantime, we recommend referring to the belt tuner webpage for the updated procedure.
The application uses your device's microphone and determines the belt tension by measuring the frequency of the vibration generated by strumming it.
Using a mobile device, open the Prusa App, and navigate to Menu >Belt Tuner. Select CORE One, then select XY-belt, and follow the in-app instructions. When ready to measure the belt frequency, tap on Start listening to use your device's microphone.
Adjusting the belt
Small adjustment
- 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 Nextruder to the frontmost Y-axis position, and to the rightmost X-axis position.
- On the front of the gantry, strum the middle of the upper belt. Place your device next to the belt during this step, to measure the frequency in Hz of the belt sound. The ideal frequency for the upper belt is 98Hz.
- On the front of the gantry, strum the middle of the lower belt. Place your device next to the belt during this step, to measure the frequency in Hz of the belt sound. The ideal frequency for the lower belt is 92Hz.
- Adjust the belts by tightening or loosening the belt tensioner screws by the same amount. A tighter bolt causes a higher frequency, and vice versa.
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Extensive adjustment
The belt tensioners should be able to solve most belt issues. However, if you need to make a larger adjustment, or the belt has slipped from the holder. To access the belt, follow the steps below.
- Remove the print head cover left and print head cover right by removing the M3x10 screws shown below.
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- Disconnect all connectors from the LoveBoard, except the main cable.
- Pull up the Bowden-bend from the fitting on top of the extruder, and unscrew the fitting. Then, open the M3x10 screws that hold the LoveBoard assembly.
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- Remove the hotend thermistor and heater cables from the cable clip. Open the thumb screws and remove the hotend, being careful with the cables.
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- Unscrew the two M3x4rT screws on the hotend cable clip, and pull it to remove the heatsink fan and heatsink thermistor cables.
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- Unscrew the M3x18 screws from the heatsink fan to remove it.
- Unscrew and remove the three M3x10 screws holding the heatsink and pull it out. Be careful with the cables.
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- Now you have access to the Nextruder holder with the belts. Make sure to add the belts that slipped out, or move the belt that is too loose. If the belt is too difficult to reattach, try loosening the belt tensioner bolts. If you need more access, unscrew the four screws that attach the holder to the carriage.
- To reassemble, follow the Assembly manual and redo the belt adjustment with the belt tuner app.
49 comments
Now I still have a layer shift problem but also a belt tension problem.
The belt tuner app (and website!) is complete and utter garbage. Please do not mistake my choice of words as a sign of frustration. It is completely and utterly worthless as it will mess up your belts and then won't help you fix it.
I tested it on two different flagship phone models from different companies, I tried the website, and it will not give you a proper reading more than 1 out of 10 times. If it does, the measures will vary widely, a range multiple times as large as your target range.
After countless tries I sometimes get the correct reading. Now I can't print anymore. It fails to calibrate the X and Y axis as it doesn't find the home position anymore. After minutes of banging the nextruder against the walls (the same thing it does 3 times in a normal run) I had to stop it.
I thoroughly regret having followed your instructions and will now try to re-tension the belts blindly as your app is worthless. If I fail, this will become a guarantee case on your end.
when I check on the printer Core one, I found the 3D item messed up as If there was a belt problem, when I checked the filament, I found it tangled.
Now I'm unable to calibrate the Y axis, no matter how many times I've followed the steps.
It appears that during the calibration process, the print head stays at the front right corner, and doesn't go to the back on the Y axis.
I've tried to initiate the Y axis calibration with the print head located to the back left, it moves normally to the right, then to the front, initiate the calibration with the same result.
Please note that the printer came assembled.
Any help is apreciated
The Prusa tuning app doesn’t work well on my Pixel 9 Pro XL, so I used the Gates Carbon Drive app with the “Motorcycle/Scooter” option, which works reliably.
Does anyone know why I can’t get different frequencies for the two belts?
Bonus question: If, with the same frequency (i.e., tension) of both belts, the gantry is perfectly aligned, will it not become distorted when the frequencies differ?
I think at least a part of the problem is that my phone has troubles picking up the frequency when the print head is on the front of Y axis.
However, the top belt now swings at 97Hz, but the lower one at 102Hz. I don't understand how to tune the two belts separately. Anyone has an idea?
I dont understand how would it be possible to get both right if both bolts should be turned the same amount. I adjusted belts to correct tensions and ignored the "same amount" part of the instructions. Time will tell if it was good idea or not.