It is recommended to perform regular maintenance on your Original Prusa MMU3 upgrade. Refer to the images below and familiarize yourself with the names of each part of the MMU3 unit.
This part guides the filament from the drive gears into the nozzle tube. Repeated loads and unloads of filament cause wear. Without the MMU, this wear is insignificant. However, a single MMU print can have thousands of filament loads and unloads, increasing the wear rate. Once this part wears out, the printer cannot properly push filament into the nozzle. Unlike the rest of the MMU parts, this is printed with Multi Jet Fusion so that the part lasts longer.
Besides the usual tools, such as Allen keys, needle-nose pliers, and IPA + paper towels, you might need:
The pulleys may be grinding the filament and its dust may accumulate around them. The best practice is to clean the pulleys with a mini-brush or a similar tool every time you run the maintenance. The pulleys also must be perfectly aligned with the filament holes, as shown in the photo below, and well tightened by the small black grub screw against the flat part of the Pulley motor axis.
Even a properly calibrated selector can be occasionally blocked with filament strings or dust or by a broken piece of filament. By pushing the right MMU button, move the selector fully to the right. Use an interdental brush or any thin wire (⌀ 1.5mm/0.06”) to push the waste through (still in service position). Use compressed air to clean any leftovers.
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