Suitable for use with a single brittle & abrasive material?  

I can't answer your question directly but the function was available in the MMU2 so I would expect it to be carried over.

https://help.prusa3d.com/article/spooljoin-mmu2s_134252

Cheerio,

RE: Suitable for use with a single brittle & abrasive material?

Thank you for the reply. Yes - I read the SpoolJoin feature is what I want to use. But I am not sure if the MMU would work with brittle or abrasive materials?

Brittle shouldn't be a problem as long as you keep the filament paths straight - perhaps don't use the buffer.   Abrasive may mean that parts wear faster but again, as long as the surfaces aren't so jagged that they stick in the guides you should be able to print OK.  What filaments are you planning to use?

Cheerio,

RE:

Metal filled filaments. I didn't know you could skip the buffer! Do you happen to have a photo or a link that shows what this would look like so I make sure that I understand? Thanks!

edit: I've not seen one of these in person so I am having a hard time visualizing how it works.

RE: Suitable for use with a single brittle & abrasive material?

How brittle is brittle? 
I have used a lot of old filaments with my mmu3, I suppose a lot depends upon your filament management setup, I do not use the Prusa MMU3 Buffer box, instead I allow my filament to free buffer in mid air. and it works OK For me. 
My table is a bit congested with a MK2/MMU1 printer at one end, and a Mk3S MMU3 printer at the other end, and 9 spool holders along the shelf above the printers
the filament spools are each screwed to the top of the shelf, and each have a short PTFE tube drilled through the rear centre of the spool holder and shelf, 
below the shelf I have longer feed tubes going to the MMU input ports, the MMU3 has 4mm x 3mm Ptfe feed tubes, to reduce friction. The setup is similar to the picture below for both printers. 

I keep the filament feed tubes short enough to have  gentle bend between the filament spool holders and the printer, to reduce friction in the PTFE and reduce the chances of filament breakages

the MMU2 / 3 parks the filaments in the MMU on top of the frame, then it has to feed the filaments about 300mm into the hotend,  purge, print, wipe, form the filament ends and retract for each filament change so the air buffer has to handle quite a lot filament. 
When using Old brittle filament, I find that  MMU3 is ok with brittle filaments whilst printing, BUT if the filaments are left loaded in the printer and standing still, for a couple or more days, the most brittle filaments tend to break in the air buffers.  (the same thing happens on a basic Mk3S if brittle filament is left on the printer for an extended period)
I haven't had issues with them breaking during prints. 

Unlike the Palette 2 S Pro, which I also have. the Palette2S has four input drive motors a cutter section, a fuser section, then a buffer feed motor into the internal common buffer.  Filaments 1 and 4 both turn through fairly sharp curves as they feed into the mechanism, filaments 2 and 3 have more gently filament paths. I had a lot of breakages with brittle filament with that device...   

as far as abrasive filament goes, in the MMU3, I haven't noticed a lot of problems in MMU and feed tubes. obviously you will need a hardened nozzle to resist the wear at the printer nozzle. 

I tend to use a hardened nozzle for all filaments. (Nozzle Z, from Zaribo, (Direct size for size replacement for the normal e3dV6 brass nozzle)).

the only brittle  filament I had problems with, was an electro conductive filament that was so brittle, it broke, as you unspooled it from the spool, 
I never got that to print and junked it, in the end. 

RE: Suitable for use with a single brittle & abrasive material?

Thanks! That really helps. I didn't realize it would work feeding freely like that. It is the most hopeful solution I've seen thus far =)

RE: Suitable for use with a single brittle & abrasive material?

I just had a quick thought - two questions:

1. How would I test to verify it is working? Is it as simple as cutting the filament to simulate run out?
2. I keep seeing reference to kinked end on the filament causing failure. Do I need to respool filament and remove the kinked end before adding it to the MMU?

RE: Suitable for use with a single brittle & abrasive material?

If you cut the filament during an mmu3 spool join print, the MMU Should sense the lack of filament, and swap to the next available spool. 

If the last section of filament on a spool has a kink in it, you can suffer with the 'Fish hook effect' where the end of the filament sprints out of line of the filament path, and jams. this is a little less of a problem with the MMU3 Finda sensor, than the Mk3 extruder, because you can undo the PTFE tube between the MMU and the extruder, and remove the end of the filament...  but it's not particularly convenient. 
It's better if you can cut the end of the filament off, before the filament runs out, or force a spool join, when the old spool gets really low, and use the remainder for odds and sods, when you can be around, to manage the end of the old filament manually. 

the UK Manufacturer 3DQF, have addressed this end of spool issue, quite nicely, they say 

Cut me free before I run out:

During the design process, we knew our spool should release the filament cleanly at the end of the roll. To allow this to happen we loop the end of the roll outside the spool so you can snip it free prior to running out. This means it will allow the tail of the filament to release cleanly at the end of the roll, and through your run-out detector (if fitted) pausing your print. Commonly on imported filament on a plastic spool, you can't get to the tail of the filament and this will normally cause no end worth of issues as it generally won't release cleanly from the spool.

https://www.3dqf.co.uk/3dqf-pla-easy-start-guide

regards Joan

RE: Suitable for use with a single brittle & abrasive material?

Thanks!

Metal filled filaments.

Beware mixing metals or printing them against each other - damp, even atmospheric humidity, can trigger electrolytic degredation and some of the products, mostly oxides, take more space and can explode a print; slowly and silently it falls apart....  but it takes a year or so to do it.

I didn't know you could skip the buffer!

There are several methods, @joantabb's is as good as any but look up auto rewinding spoolholders as another (printable) option.

                                               *  *  *

the only brittle filament I had problems with, was an electro conductive filament that was so brittle, it broke, as you unspooled it

Was this a sample of the high density graphene filled prototype filament from a certain British manufacturer at TCT360 which they were asking for user test feedback on?  AIui they don't want to be named until it is ready for release.  It was very temperamental and graphene is such a good thermal conductor that heating and cooling were screwed up as well.  I did get some very simple circuits printed the manual MMU way but the stuff is also fragile after printing.  Did you try their other, low graphene density non-conductive sample? I found it much nicer to use, very stiff, I fancy that one might be on the market soon.

Cheerio,

RE: Suitable for use with a single brittle & abrasive material?

Hi Diem. No I didn't see those filaments at tct360.

I wanted to print antistatic modules for smokeless powder handling.