Prusa Research i3 MK3S+, Manual

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5. E-axis assembly
58 Original Prusa i3 MK3S+ kit assembly
STEP 9 Bondtech gear assembly
Take the Extruder-motor-plate and secure it using two M3x10 screws . Use the
cable as a guide to properly orient the part.
Resist the temptation to place a screw in the third hole! Leave it for later ;)
Rotate the shaft as in the picture. Flat part must face in the direction of the arrow.
Slide the gear on the shaft, the set screw must be facing against the flat part of the
shaft. Tighten the screw slightly.
There is a "channel" for the filament inside the printed part. Align approximately the
teeth on the gear with it.
Don't tighten the screw just yet. We will align it properly first. See the next step.
STEP 10 Bondtech gear alignment
Take a piece of the 1.75 filament. You can use the bundled one on a spool, don't use
the black nylon, which is too thick. Straighten the filament as much as possible.
Place the filament along the path and align the gear properly.
The filament will be always slightly bent. Use it anyway for the initial alignment.
For a final check replace the filament with an Allen key. Bear in mind, the key has
slightly different size than the filament.
Tighten the screw slightly to temporarily fix it, we will make the final check and
tightening later on. Be careful, you can strip the thread.
Don't use any glue to fix the screw in place, you won't be able to release it, in such
case you might have to replace the entire motor.