My belts are wearing and squeaking. The culprit is the idler pulley. In RepRap spirit, why buy when I can design and print a new one.
Toothed -> gentler on belt to improve longevity and smoother entry/exit
ComfortFit flange -> smooth profile is gentler on belt edges and eliminates squeaking
Dual ball bearing -> more stable, less wobble and smoother
This is designed to exact GT2 belt profile specification. If you have any fit issues, your belt may not be to spec, such as tooth or pitch line.
You will need two 623 bearings per pulley, such as: https://www.amazon.com/gp/product/B01G7L3B74/ref=oh_aui_detailpage_o09_s02?ie=UTF8&psc=1
I included two sizes of pulley, a 22T and 24T. 22T is more standard but 24T prints a little cleaner with the larger diameter.
To clear up some confusion, the effective diameter of the 22T pulley is the same as the smooth pulley that comes stock on Prusa. This is because the belt teeth fit into the pulley teeth so the belt pitch diameter works out nearly identical.
Outside dimensions are 9mm (9.4 with washers) x 18mm diameter. Flange is 1mm so 7mm belt path. GT2 is 6mm +/- 0.2mm typical.
You really should use s 0.25mm nozzle or similar. It might work with 0.4 nozzle, but likely not as accurate of fit. I think it is impressive to "manufacture" something to this level of precision at home. Enjoy.
Update I added a version that should print well with a standard 0.4 nozzle.
Also need to print 0.05 layer height to get the smooth ComfortFit flange. I included gcode that is dual layer, 0.05 for the flange and 0.1 for the rest. I recommend PLA. Note that the washer prints in the middle so don't throw away.
If using Slic3r, I recommend these settings (already in supplied gcode): 0% infill, limit speed to 20 mm/s for 0.25 nozzle, 4 perimeters, turn off "ensure vertical wall thickness". You can use 'split' to separate out the washer and can scale it in Z direction if you want a tighter fit.
Build is simple:
Print two, press in a 623 bearing on each side, sandwich together, add washers and install. See photo. Inserting horizontal helps keep the washers in place while you slide it in. The washers should prevent you from over tightening, but make sure it spins freely.
I included a test_moves gcode you can run that moves your X and Y axes in a square, X, circle, fast and slow over full range (Prusa bed) to see if everything is well behaved. Easy to hack the file if you want to change.
see Taurus line of upgrades for best performance.
I have many parts for MK3. I like them all, but here is what I recommend to tighten things up and improve reliability and print quality. This is based on my own experience using these parts and from others using the same or similar upgrades. YMMV.
Z mounts - fix alignment, sturdier
Y endstop - fix layer shift, long term reliability
hard feet - reduce vibrations
stable pulley - stabilize belt, longevity
runner - offload frame, poor man's reverse-bowden