SpoolJoin (MMU2S) | Prusa Knowledge Base

If you have spools with just a small amount of filament, and not enough for a print, you do not need to throw them away, or manually change the filament every time it ends. You can use the MMU2S feature of filament depletion, called SpoolJoin.

This feature will automatically switch to the next filament in line, should you run out. In order to activate it, go to LCD Menu - Settings - SpoolJoin [On/Off]. Add each spool that you wish to finish on the MMU2S (do not skip any filament slot in between). Once the filament depletes, the printer will unload it and load the next slot.

The function works sequentially in a loop, switching from filament 1 to 2, then 2 to 3, and so forth. The switching occurs when the FINDA sensor detects the current spool is finished. While the printer is going through filament slots, you can replace the spools on the slots that have run out, and when the filament in slot 5 ends, it will go back to slot 1 and continue.

After an unload, there will be filament on the filament slot: even if you are not replacing the spool once it runs out, you'll have to remove the filament leftover by hand. Alternatively, you can do this after finishing the print, choose in LCD Menu - Eject filament - Eject Filament 1/2/3/4/5.

We recommend turning the SpoolJoin feature off for multi-material prints. As an example, suppose your multi-material print uses filaments 1 and 2. If filament 1 runs out or run-out is falsely detected, filament 2 will be used in both places, as filament 1 is considered empty.

There is a niche use of SpoolJoin when printing multi-material models. If you have a two-color print and, in PrusaSlicer, set it to use Filament 1 and 3, there is now a spare spool loaded to Filament 2. This will be used when Filament 1 runs out. In addition, Filament 4 and 5 can be loaded before printing with the same intention, substituting for Filament 3.

Filaments are often "secured" to the spool by a bent end (Blue circle). This might make your filament get stuck in the MMU2S PTFE tubes or pull the empty spool. Make sure to cut that end when you are finishing a spool.

10 comments

Eddie Louw

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3 months ago

Where is the spool join setting on MK4S MMU3?

Mike1D

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6 months ago

Please update the description that it will work with MMU3, too.(unless that feature has been removed which I don't hope - waiting for my MMU3 to be delivered)Also it might be useful to add this information (or a link to it) to the online handbook of MMU3. I was searching for that feature for quite a while and even no reply in the forum. I found it the using google at a reddit forum.

MMPLLC

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over 1 year ago

I have an MMU3 on a Mk3S that is pretty well dialed in. For the "niche" use of SpoolJoin, it says to preload spools 1 and 3, and the print sliced to use them as such, with spool 2 as the backup, and the printer will use spool 2 when spool 1 runs out. It also says that when spool 5 runs out, ti will move on to spool 1. Do these two tactics work in conjuntion? I currently do a lot of prints that use 3 and sometimes 4 spools, and I have the prints sliced to use spools 1-4. Can I slice a print to use spool 5 instead of spool 1, turn on SpoolJoin with spool 1 as the back up, and expect it to use spool 1 once spool 5 runs out, while still using spools 2-4 normally?

bryn51

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over 2 years ago

This article could elaborate more on how the spool join feature actually works. Does it sense the end of a roll using the Finda sensor ? If so then how would it unload the old filament ?

Giuliano - Official Prusa CS

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over 2 years ago

Hello. The FINDA senses the end of the filament. With the Spool Join function enabled, instead of waiting for the manual spool change, the selector will move to the right to pick up the next filament when the FINDA doesn't detect the filament any longer.

Emanuele

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over 2 years ago

Durante la stampa, se il filamento finisce, la stampante mi chiede di estrarre il filamento rimasto, ma non me lo espelle e se clicco mi ricarica lo spezzone di filamento rimasto.È un bug o perchè stampo attraverso Octoprint?
During printing, if the filament runs out, the printer asks me to extract the remaining filament, but it does not eject it and if I click it reloads the remaining piece of filament. Is it a bug or why do I print through Octoprint?

Giuliano - Official Prusa CS

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over 2 years ago

Hello. It could be because of Octoprint. You can try to disconnect it and see if the error persists.