Adjusting belt tension (CORE One) | Prusa Knowledge Base

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.

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

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 rearmost Y-axis position, and to the center of the X-axis.
On the left and the right sides, strum the belts in the middle. Place your device next to the belts during this step, to measure the frequency in Hz of the belt sound.
The strumming sound frequency is typically between 80-90 Hz, with the ideal value at 85 Hz.
Adjust the belts by tightening or loosening the belt tensioner screws. A tighter bolt causes a higher frequency, and vice versa.
It is fundamental for belts to have ideally the same frequency, or at most a very small difference, up to 3 Hz.

12 comments

tumes

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This isn’t quite as complicated as it seems and following the instructions exactly fixed my homing loop in under 3 minutes of work. I would suggest this procedure:

1. Follow the instructions to eliminate play on both sides by loosening them asymmetrically (eg the side without play gets a quarter turn and the side with play gets 1/8th turn or less)
2. Tighten them symmetrically from that point until both sides are on either side of the 85hz target (eg tighten both sides 1/4 turn, check frequencies, repeat until one is above 85 and one is below).
3. Bring the gantry to the front and check for play again and repeat the procedure from step 1 until there is none. Ideally these will be small moves at this point.
4. Move the gantry to the back and fine tune anything way out of spec.

You may have to repeat 3 and 4 a few times at the end but it took very little time for me to hone it in and it instantly homes on its first try right after.

pstimpel

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I am sorry, but I have never seen such a ....

Guys, I need to tension the belts on my Prusa assembled Printer I received one day ago? Your firmware is telling me so with a nice red screen!

Then I need to use the app, because my laptop is too big. OK, the app asks for an account, for belt tensioning?

Belts frequencies are showing something between 50 and 170 Hertz ... while in reality it is something between 75 and 90 for sure. The App is useless, it seems.

This is not my first prusa printers, and I had kits and ready assembled ones... but this Core One here is a nightmare so far ...

koesterakis

•

You don't need the app. Just read this article.
Go to belt.connect.prusa3d.com on your phone. You don't need to log in.
It's that easy if you would just read.

chking

•

The website tuner isn't much better.

wbphelps

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after doing a very careful tuning, and getting 85 hz on both belts, and perfect alignment at the front, I ran a check using the GT2 belt tension device available on Printables and got 2.4 exactly on both belts...

Geltenus

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Hi. Could You please check the tension with https://www.printables.com/model/46639-tension-meter-for-the-gt2-belts-of-i3-mk3s-or-prus ? I am wondering if it will show closer to the max value. Thanks in advance.

Geltenus

•

Finally checked by myself. I had to bend according to https://forum.prusa3d.com/forum/postid/738308/ Tension meter printed in Devil Design PETG (black color). 85Hz is shown when the whole arm is just above MIN value. Printed tension meter twice, both show the same behavior. Using both of them, tensioning was a breeze. Managed to have 85/86Hz.

btarlton

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Please update this guide to be more clear. After spending over 10 hours assembling my Core One kit, I got to this step and it took me 2 hours to finally get things working because the instructions are not clear and the app is very inconsistent at picking up the frequency. I ended up using a laptop and an external microphone with the web based tuner for the best results. To keep there from being a gap in the corners, I ended up having to have my right side tighter than my left. The left side for me is in the low 80's and the right side is in the upper 90's. It passes calibration and seems to print fine this way. Been printing for 3 days straight now. But I would like to know if the frequency of each side being equal is more important than getting the gap out on each side. None of this is intuitive and the instructions are unclear.

Versayce

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I second this. The readings from the phone are pretty inconsistent. I ended up laying my phone on the build plate while strumming to get best results. This works similarly to a guitar tuner, but every guitar tuner I've used on the phone seem to do a better job at picking up frequencies and giving accurate readings that I have verified using my accurate tuning pedals. This is likely due to the belt being less resonant and loud than guitar strings, but it's hard to have a high degree of confidence in my belt tension after using the app and a more robust solution would be welcome. Either way, my prints are still coming along very well.

RFT2112

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Looking at the pics of the position of the head I can see tow belts on either side. this tells me that the head is in the formost position or closest to the door, Am I seeing this wrong?
Prusa really just needs to make a video of this for clarity.