This chapter will guide you through calibrating and preparing the printer for its first run. Starting with tensioning the belts:
⬢The left screw adjusts the upper belt.
⬢The right screw adjusts the lower belt.
⬢Double-check that the M3x30 screws in the belt tensioners were lubricated during assembly.
WARNING: Incorrect procedure may result in damage to plastic parts or seizing of screws. Before adjusting the belt tension, read the dedicated article:
I absolutely HATE tightening Prusa belts. I wasted a ton of time on this one. I was busily strumming, but kept getting vastly different results. I ended up downloading a separate app to ascertain what frequency the belts were, and found that they had considerably over-tightened (frequencies of ~250 Hz) which had happened simply screwing a few turns. I strongly suggest playing 98Hz on your computer/phone, and adjusting the belt tightness to approximate the sound before doing any of the processes described on this page or the accompanying belt tuning page!
I spent a while on the belt tension step as I think I had at least one belt one tooth too short (see my post in the X/Y belt securing step). I could not get the belt tensioner app working on my older iPhone with safari, as it would never display the frequency.
I did use the built-in tuning function (manual belt tuning) on the printer that vibrates the belt with a strobe so you can see the swing of the belt at the resonate frequency. The description of the swing is not that great. It will SWING, you will see it. I made the mistake of seeing a small swing and thinking that was what I was looking for. If you are thinking to yourself, maybe that is the swing... it is not. Once I went back and re-secured the belts at 3-4 teeth showing I was able to see the swing and the pulleys where not hitting the gantry at home (causing home calibration failure). Also it may be that both belts are at the same frequency, so when you set the freq for one belt the other may also resonate at the same freq. so they both move at pretty much the same resonate freq. Both of mine ended up at 92.5Hz.
Prusa has a BETA belt tensioner based on hertz of the belt vibration. The key is to pluck the belts in the front of the printer, not the sides. Open the link on your cell phone and give it access to your microphone. It says the top and bottom belts should have a 92 hertz sound to them when plucked.
It's easy to have the belts much too loose, but have the phone app say they are okay, because it can show a harmonic (2 times the actual frequency). The belts should give a nice clear tone when you pluck them, not a dull fluttering sound.
Due to our belts being too short, they came undone in the nextruder holder during the calibration process and had to uninstall the printer head and other wires to diagnose the issue. We don't want them to come undone in the middle of a print, so we'll have to reach out to Prusa support for two belts or may order the same type online.
I did use the built-in tuning function (manual belt tuning) on the printer that vibrates the belt with a strobe so you can see the swing of the belt at the resonate frequency. The description of the swing is not that great. It will SWING, you will see it. I made the mistake of seeing a small swing and thinking that was what I was looking for. If you are thinking to yourself, maybe that is the swing... it is not. Once I went back and re-secured the belts at 3-4 teeth showing I was able to see the swing and the pulleys where not hitting the gantry at home (causing home calibration failure). Also it may be that both belts are at the same frequency, so when you set the freq for one belt the other may also resonate at the same freq. so they both move at pretty much the same resonate freq. Both of mine ended up at 92.5Hz.
https://belt.connect.prusa3d.com/