This is where I found that the M3nS nuts inserted into the belt-tensioner-pullies BOTH somehow managed to cross-thread and lock up. Even after stripping the body apart to try and free them, I couldn't and the nut started to spin inside the belt-tensioner-pulley. These are captive nuts and bolts and we have no control over how they thread so I can only assume that the slot for the nut in the belt-tensioner-pulley is too loose or not vertical. I now need to replace them both.
If you are anything like me, I strongly recommend you take a coffee break at this point and avoid my mistakes.
The prusa app's belt tuner was complete junk for me, and the website did not first work any better. Mistakes were made and belt got out from the end, and it was real fun getting it back.
Some time later I downloaded a guitar tuning app, and with that got it to 85hz with ease. Then tried the prusa website and magically it worked fine too now.
Read this before going to the guide! So, look, when you´re checking if the gantry is square by checking the play between the gantry and tensioners, make your belt as relaxed as possible. Now, check if the gantry is squared while the belt is relaxed, if it is not squared, you´ll need to bend the X gantry towards the side with the play, you can do it by putting a wrench between the tensioner and side with no play, then pull the side with the play towards the tensioner, repeat until it lies flat on it just like another side. If it doesn´t work, ask support. Now, if both sides have none or extremely small amount of play (less than 0.5mm is best, otherwise XY skew error is possible and homing problems) start tensioning the belts, but, be careful, do it evenly on both sides, 1 rotation X= 1 rotation Y, inbetween the stages move the gantry around to evenly spread the tension. When belts sound like low guitar bass, start using some kind of tuning app or guitar tuning tool, I personally used ''Tuner-Pitched'' app, as Prusa tensioning application doesn´t work well. Be sure your room is silent, now try to fit your belt pitch into 80-90hz range, ATTENTION! STILL ONLY TENSION WITH EVEN ROTATIONS, the reason for that being that uneven tensioning will cause play on endstops=non square gantry. As the guide states, tolerance of 3 hz is allowed between sides, and from my experience it works perfectly well as for me 85hz X and 88hz Y. After every small correction still move the gantry around 2-3 times to spread tension, don´t forget that. NOW, if your tolerance is higher than 3, you can try to correct is by seperately tensioning the X and Y axis, but, CAREFUL, is coreXY system, if you tension 1 side, other one gets tensioned slightly too, so don´t try to change both X and Y tension in different directions at the same time, tension one, move the gantry and check pitch again, that precise correction will be the most annoying part of tensioning process, but it´s worth it over rushing things, trust me I know from experience of 0.3% XY skew error on califlower and non ending extruder headbanging...
After you got the pitch, recheck if the gantry is square, recheck if tensioning screws change position, if yes move the gantry around more and retension the screws to the same positon until they stop moving from where they should be. If gantry is not square go back to the start and try again, if it repeatedly doesn´t fit, contact support. I hope this helps someone who was confused same as me and needed to bend the gantry to finally fix layer shift issues and long homing process
Thanks for the tips! For me, after relaxing the belt, I had to slightly add tension on both side for the gantry to be squared. It was just to loose to stay in place.
For the tuning, I would recommend the app "Phyphox". It makes the most of your phone's sensors, from gps to gyroscope, including your microphone. The tool "Audio Spectrum" is quite handy here as it allow you to setup a timed experiment: set it for a duration of 2-3 seconds. It will then give you the peak-frequency you are looking for (just ensure the accuracy is set to the highest value in the parameters).
The pictures in the instructions are misleading; I noticed that holding the phone in hand causes a lack of readings or readings above 130 Hz. It's best to lay the phone on a heatbed, then it's easy to adjust the belts.
These are captive nuts and bolts and we have no control over how they thread so I can only assume that the slot for the nut in the belt-tensioner-pulley is too loose or not vertical.
I now need to replace them both.
The prusa app's belt tuner was complete junk for me, and the website did not first work any better. Mistakes were made and belt got out from the end, and it was real fun getting it back.
Some time later I downloaded a guitar tuning app, and with that got it to 85hz with ease. Then tried the prusa website and magically it worked fine too now.
So, look, when you´re checking if the gantry is square by checking the play between the gantry and tensioners, make your belt as relaxed as possible.
Now, check if the gantry is squared while the belt is relaxed, if it is not squared, you´ll need to bend the X gantry towards the side with the play, you can do it by putting a wrench between the tensioner and side with no play, then pull the side with the play towards the tensioner, repeat until it lies flat on it just like another side.
If it doesn´t work, ask support.
Now, if both sides have none or extremely small amount of play (less than 0.5mm is best, otherwise XY skew error is possible and homing problems)
start tensioning the belts, but, be careful, do it evenly on both sides, 1 rotation X= 1 rotation Y, inbetween the stages move the gantry around to evenly spread the tension. When belts sound like low guitar bass, start using some kind of tuning app or guitar tuning tool, I personally used ''Tuner-Pitched'' app, as Prusa tensioning application doesn´t work well.
Be sure your room is silent, now try to fit your belt pitch into 80-90hz range, ATTENTION! STILL ONLY TENSION WITH EVEN ROTATIONS, the reason for that being that uneven tensioning will cause play on endstops=non square gantry. As the guide states, tolerance of 3 hz is allowed between sides, and from my experience it works perfectly well as for me 85hz X and 88hz Y. After every small correction still move the gantry around 2-3 times to spread tension, don´t forget that.
NOW, if your tolerance is higher than 3, you can try to correct is by seperately tensioning the X and Y axis, but, CAREFUL, is coreXY system, if you tension 1 side, other one gets tensioned slightly too, so don´t try to change both X and Y tension in different directions at the same time, tension one, move the gantry and check pitch again, that precise correction will be the most annoying part of tensioning process, but it´s worth it over rushing things, trust me I know from experience of 0.3% XY skew error on califlower and non ending extruder headbanging...
After you got the pitch, recheck if the gantry is square, recheck if tensioning screws change position, if yes move the gantry around more and retension the screws to the same positon until they stop moving from where they should be. If gantry is not square go back to the start and try again, if it repeatedly doesn´t fit, contact support. I hope this helps someone who was confused same as me and needed to bend the gantry to finally fix layer shift issues and long homing process
For me, after relaxing the belt, I had to slightly add tension on both side for the gantry to be squared. It was just to loose to stay in place.
For the tuning, I would recommend the app "Phyphox". It makes the most of your phone's sensors, from gps to gyroscope, including your microphone. The tool "Audio Spectrum" is quite handy here as it allow you to setup a timed experiment: set it for a duration of 2-3 seconds. It will then give you the peak-frequency you are looking for (just ensure the accuracy is set to the highest value in the parameters).