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Spool join feature is useless...  

Active Member
Spool join feature is useless...

The spool join feature is one of the reasons I bought the mmu2 upgrade. But it simply does not work in a real world scenario. 

This is what I mean,


I did extensive testing, disassembly/reassembly to get multiple 'test lengths' of filament to 'spool join'. Meaning I cut off 2-3 feet of filament and loaded for each extruder and did a test print for the spool join feature.

There were occasional failures when the MMU2 tries to unload the extruder and pushes the 'tail end' of the filament back  through the selector and beyond the pulley bondtech gears towards the spool. The failure mode is the tail end of the filament jams between the selector and guide ports to the bondtech gears.

But in a REAL WORLD application, when dealing with the actual END of a spool, failure is 100%. Primarily because most spools have the tail end 'bent' into an eye on the center spool. This causes the non-straight end to ALWAYS jam when the MMU2 tries to unload the tail when the 'end of spool' is detected.

Even if you are lucky enough to have minimal filament left on the spool, and are able to take a snub nose cutter and cut the tail end 'bend' deep towards the center of the spool, it does not provide a straight enough tail end for it to be sent back through selector and pulley. It just JAMS, the mmu2 enters some error mode, and (as far as I can tell) there is no way to tell it that you have manually unloaded the  filament and proceed to load the next extruder.

Of course, with the prints I do, there still may be a number of layers left on the spool, that, are not enough for another print, but is too loaded up to even get at the tail to snip the end.

To get that close to the end of the spool, means you dont have much left anyway, and the effort to use the little remaining filament is just not worth it.


Again, the "Spool Join" feature is useless.





Posted : 29/08/2019 5:32 am
AndyPants liked
New Member
RE: Spool join feature is useless...

I fully agree with you. At beginning it was maybe a good wish from developer but in reality it is bullshit. I lost four hours print because next fillament was not loaded and printer hung saying "filament loading" with no way to continue.

Posted : 07/12/2019 2:19 pm
Estimable Member
RE: Spool join feature is useless...

As the rest of the MMU it is a nice idea not well thought-out. 

That being said, I just printed some parts with one sucessful spool join. What I did

  • I had a filament sample not wound too tightly
  • I put it on a 17 cm diameter sample holder
  • I straightened the end as far as possible and made a conical cut at the end
  • I made sure the end was loose on the sample spool holder.

So under these circumstances spool join can work. It will 100% fail as robert wrote when using with a regular spool nearing its end.

- Martin

Posted : 07/12/2019 2:57 pm
RE: Spool join feature is useless...

I have a large print running now with spooljoin enabled. I happened to be at the printer when the first spool ran out of filament. Unfortunately the printer just keep going after the last of the filament was drawn into the extruder. Nothing stopped to change to the next spool. I manually paused the print and then tried to load to nozzle the next filiment which kept loading, unloading, loading, unloading until it finally errored out. after a lot of finagling and trial and error I was able to get a the second spool loaded and resume the print. I lost a couple of layers so there's an obvious weak spot where the layers were much larger than 0.3mm but it seems to be continuing OK. I wish spooljoin worked as advertised....


Posted : 11/06/2023 2:00 am
Eminent Member
RE: Spool join feature is useless...

I have been using the MMU3 on a Mk3S+, and have had 100% success with the SpoolJoin function. I love the feature. That said.....


My problem is that it isn't functional with multi color prints. The dev team needs to work out this function to allow for the assignment of successive spools, so that when a spool runs out, the MMU will subsequently use the assigned successor spool in place of the spool called for in the program.


CNC machining centers have been doing this for quite a while now. The machine can be set up so that there are multiple tool pots in the carousel that are assigned to, say, "T1", so that, when the machine decides that the actual "T1" has had it, either by machining time or spindle load, for example, the machine will, from that point, load a tool from a different pot that has been assigned as a successor to T1. I see no reason the SpoolJoin function cannot follow this same behavior. When spool 1 runs out, the MMU uses, say, spool 5 when the program calls for spool 1. Dev team? You listening?


Thanks. Brad.

Posted : 18/10/2023 11:52 am