Gearbox alignment (CORE One L, CORE One, XL, MK4/S, MK3.9/S)

On the Prusa CORE One L, CORE One, Original Prusa MK4/S, MK3.9/S, and XL, a gearbox alignment is necessary for user-assembled or serviced gearboxes. This procedure is part of the Selftest or can be initiated from LCD menu -> Control -> Calibrations & tests -> Gears Calibration.

Once the procedure is initiated, the printer will prompt for the calibration to start. Press "Continue".

The CORE One L and XL do not need to go through the gear calibration on arrival, as it is pre-assembled, only if the extruder is disassembled and reassembled. The process is the same as for the CORE One and MK4/S, MK3.9/S pictured below.

Slightly loosen the three bolts on the gearbox cover, by one turn and a half, then unlock and open the idler. When done, press "Continue".

The printer will go through the automatic gearbox alignment. This process can’t be seen from the outside. Once prompted, tighten the three screws in the pattern indicated on the screen, and close the idler.

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3 comments

Sven Weidenmann

•

Used Ninja Flex and could not unload. Used Ninja flex before couple of times. Excellent support, guided me through this first time experiance not working of unload. In my case, i had to fully remove nextruder with gear. Did use the gear allignement tool (E1) which came with the MK4S upgrade Kit and makes the critical adjustment much easier. I did trust the 1.5 turn instruction and final adjustment did work. Using my MK4 since 2 years with lot of prints, upgraded 1 year ago to MK4s. I had a situation where i felt the 3 screws does not fit anymore perfect. Thats was solved once i did remove the hole assemebly and re-assembled it back.

ljhms

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As someone noted in the comments of the Core One assembly kit: When the on-screen instructions tell you to "lightly" tighten the screws, they should still be snug. That is, they shouldn't be so loose that there is any play or that they work themselves out over time due to vibrations. Not doing it correctly was one source of random Z-banding/uneven layers on my machine that got worse over time, as the screws loosened. The point is that you shouldn't over-tighten anything. Not sure if the calibration detects it and warns you if you cause the mechanics to bind up or not, but finger-tight (using the small end of the allen key as a handle, putting only the lightest tension you can on the handle) seems enough.

One thing that isn't immediately obvious is that these screws are the only thing that fix the E-motor and gearbox assembly in space, relative to the extruder carriage and nozzle, so if there is any play in it, it could put uneven pressure on the filament, giving small variations in the extrusion.

I agree with the others about the directions on screen being contradictory when loosening them as well. Does it mean the top of the screw head should be flush with the cover plate, or the bottom? If it's the top, that's not possible, since unscrewing them 1.5 turns makes it poke out more than that (about half a millimeter, maybe). And making the bottom of the head flush would require significantly more turns. What I did was to follow the "1.5 turns" instruction and trust that. Maybe they mean you should pull out the (now loose) cover to make it flush with the screw heads?

In any case, after tightening them down again, the top of the screw heads are slightly below the surface of the cover. Not much, but half a millimeter at most.

dpow

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This is slightly confusing - arent the screws already supposed to be flush with the face? Rotating them 1.5x would make them not flush

RFT2112

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Exactly!