Adjusting belt tension (XL) | Prusa Knowledge Base

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.

Tightening the right Y-axis rail reduces the space between the CoreXY Front Left and the X-axis on the right side but creates space on the left side, and vice versa.

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.

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.

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36 comments

Atle Dreier

•

I can't get the app happy. With the gantry square, I cannot get the belt tuning right.

Any advice? Core One, prebuilt.

michanisani

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The enable mic do not work with samsung M52 phone. Last android 13

Chris T

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I was getting very frustrated trying to use the belt tuning app. The app seems very unresponsive BUT if you do it from the website via a browser it works much better.

I kept getting constant readings of 120 Hz and telling me to loosen the belt. Well in order for the tuning to work appropriately the belt needs to be decently tightened before it will actually register appropriately. Once I got it to that point making adjustments to the appropriate frequency was much easier and consistently sounds much better.

Running a homing tower now to see if everything looks good.

3D Medic Vince

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I just had to redo the alignment of the axis as the right side wasn't touching the front like the left side. I went to retune and the app wouldn't work but if I put my phone in airplane mode it would. I assume there's probably an app that's blocking the Prusa app from using the mic but after airplane mode worked great.

senatorpjt

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I couldn't reliably get the app to pick up a result. What I ended up doing is just finding a 10 minute recording of an 80Hz triangle wave and tuning it by ear. https://www.youtube.com/watch?v=CHdMV2PROLE

P Perry

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Actually you can get it to pick up if the phone mic is less than 3mm from the belt. Not sure why it is tuned this way, but keeping it that close and strumming it with 83 Hz fixed almost all of my layer shifts. What remains I believe is coming from another issue.

Redshift Z8

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Hello All, this is a pathetic method of checking the belt tension on this machine. If you really want to get it perfect you need the correct tool for the job, I brought a proper belt tension test tool. It was like a few pounds. Here is a link https://www.ebay.co.uk/itm/226619618474 its a precise and easy tool to use. The reading i find works is 8.35 This entire strum the belt thing is ridiculas, to many variables, type of phone, type of microphone, type of software, way you strum, how long your finger nails are. if your using skin or nails. The entire thing is stupid. This tool gives you a precise reading. simples!!!. Best thing i ever brought for the xl and its like 12 quid. Also PRUSA please just give us the offical reading required for one of these tools out of curiousity. BETTER STILL INCLUDE a prusa one in the sale of the machine. Surly it would save you massive man power resources helping people with their belts. INCLUDE ONE FOR GOD SAKE PRUSA. Just do it. ALSO surly you have to run a input shaper test after doing anything to your belts.

P Perry

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The lack of actual videos or decent documentation has made that tool almost equally useless.

I’ve found that the sound works to make sure both sides are the same and doing test prints with the tower will allow you to find the right range. Once you do that, you can align the two sides with the tone and it will likely end up flawless.