Filament not loading to extruder
I have just gotten a mmu2s second hand, for my mk3s+, but it is barely used. I have now set it up, but when i try loading the filament, the mmu pushes the filament throgh the tube from the mmu to the extruder until the filament activates the ir sensor, and then the mmu disengages. Then the extruder bondtech gears first pull the filament a bit down into the extruder, then pushes it up, to a point where it sometimes cant grip it again, other times not the case, then pulls it a little bit down again, and then pushes it up again, where the mmu takes the filament back, and gives me the failed to load message. Sometimes, the gears grind so much on the filament (im using PLA), that it gets stuck, and i have to disassemble it to get the filament out. (and i have made sure to cut the filament tip correctly before loading)
I have calibrated the ir sensor and the FINDA and they seem to work fine, i have tightened the screws like prusa says to, but nothing works. I have also tested there is almost no friction in the setup, and i also tried to remove the ptfe tube from the extruder, loosened the idler door screw (i think that is what its called - correct me if im wrong), and then tried manually inserting filament while the printer was hot, and there was absolutely no problems. The filament just went straight down and out of the nozzle.
My theory is that the mmu isnt pushing the filament far enough, but im not sure.
I also tried calibrating the bowden tube length but i cant find anything on how to get that to work.
If anyone knows something i would really appreciate it, becuse i have spent several frustrating hours on this, but nothing seems to work.
RE: Filament not loading to extruder
I would upgrade it to MMU3
regards Joan
I try to make safe suggestions,You should understand the context and ensure you are happy that they are safe before attempting to apply my suggestions, what you do, is YOUR responsibility.Location Halifax UK
RE: Filament not loading to extruder
Hi Joan
I want to make sure that there is no other good option, before i start spending to much money. If you know any other solution i would really like to know.
If no could you provide me with a material list, or somewhere i can get the upgrade kit.
Thank you
MMU3 Info
Hi Magnus,
I am not a Prusa employee so forgive the unprofessional links and suggestions below
I got my MMU2 working much better by changing out all of the the PTFE Tubes from 2mm ID to 2.5mm ID tubes... More recently Prusa decided to use 3mm ID Ptfe Tubes...
a number of people had power problems with MMU2 and did DIY Power upgrades... Prusa now offer a PD Board upgrade (available on the prusa spares pages) as part of the MMU2 to MMU3 upgrade, there is a link below for a clone version (the PD Board also needs a new power and data cable)
This thread may help you,
Some people have just upgraded the MMU2 power and loaded MMU3 firmware (the controller board is the same for MMU2 and MMU3)
Some people have changed to UltiMulti to improve the MMU Plastics
https://github.com/davidkerny/BUZA-ULTIMULTI
the MMU3 plastics have been updated to improve filament paths and replace the original idler drum with a revised drum with aluminium coupler (the MMU2 Idler drum was a bit fragile around the motor connection, over tightening the motor shaft screws could split the original idler drum.
there are improved MMU2 drum STL's on Prusa printables, there are also printable motor connectors on printables to allow connection of the MMU3 idler drum without the aluminium fitting from the upgrade kit.
the MMU3 Selector now has two cutter blades, you may still have a spare blade from the original MMU2 build, that you could use for the second blade...
the selector for the MMU3 now has a vent to allow particles of filament strings to escape from the Finda chamber, and it uas a magnet and steel ball, to improve the Finda operation... (Note the ball used in the selector must be attracted by the magnet, (Some ball bearings are not attracted by magnets) the magnet is the same as the small magnet from the original Mk3S filament sensor so you may well have a spare, available)
the original MMU2 to MMU3 kit had e3d filament collets to retain the filament feed PTFE tubes, there is an alternative for the MMU3 on printables https://www.printables.com/model/693548-mmu3-collet-holder-r3-pc4m10-conical
the original Mk3S filament sensor tower is hard to adjust, there is a revised version in the original prusa MMU3 printable parts on printables in the mk3S+ section...
other improved filament sensor towers are also available in printables...
In My opinion, the single most helpful item for MMU2/3 is a filament sensor with an LED Indicator, it makes filament sensor adjustment much much easier...
I Upgraded my filament sensor by adding a 5volt LED, directly to the filament sensor 
this was my MMU2
this was where I connected the LED!
A modified filament sensor is available from Zaribo
https://zaribo.com/sensors/546-5033-zaribo-smart-prusa-filament-sensor-for-3d-printers.html#/177-smart_fs_accessories-none 
Prusa offer modified PTFE Connectors which had a larger internal diameter
but I use these
I use 360degree swivel connectors on my Mk3.9 MMU3
BUT these can collide with the MMU3 at high print heights,
SOOO... I use modified MMU3 Mounts
mmu3-Horiz-mount-enclosure-offset30mm (1) Found on Printables
Useful info
https://forum.prusa3d.com/forum/original-prusa-i3-mmu3-general-discussion-announcements-and-releases/mmu2s-to-mmu3-upgrade-info/paged/2/
or this
https://help.prusa3d.com/article/list-of-parts-for-mmu2s-to-mmu3-upgrades_887521
I have never used the clone PD Board and cable myself, but I have heard that it helps
https://www.ebay.co.uk/itm/236387035252?_skw=prusa+mmu3&itmmeta=01KA3GK712CR7EXJQTSGXFFCSG&hash=item3709c3e874:g:dOEAAeSwo1Bo7QhL&itmprp=enc%3AAQAKAAAA8FkggFvd1GGDu0w3yXCmi1c6zuaR5wdsKNgpuSaTQrn%2FkbjhKBT%2BjvG0m4zxZQLL1FE3ZieNfAMY3n3LITcLTgxTch9tNiBU9IxPNs4vAGN%2BBIkUUGnDTXHwP7ufXJeSyGEMLPnLkB2Vjky7Hu6VXO6BRf%2BlNEoR9zAw1Goy7%2BYB6yIK7o0Hcpz9cpEP9gPK84s8hd6amac83ebqJ%2BkgFGOnAsQEWR4ETN8bWh2EHhIL07fOHL1JPbmeYf74VrH%2BKJh6iF3CF3O22A9INgztxbYlUDvvgoxtyPNy8moGp3Wfa0SNqbz399NK544E8LWRsg%3D%3D%7Ctkp%3ABk9SR4rxzPDQZg
Regards Joan
I try to make safe suggestions,You should understand the context and ensure you are happy that they are safe before attempting to apply my suggestions, what you do, is YOUR responsibility.Location Halifax UK
RE: Filament not loading to extruder
Thank you very much for the advice. I will try out some of these things to see if they work.
I just have one question though: Why is it that when the filament reaches the extruder, the bondtech gears pulls it down, then pushes it up, then down again and then up again? Because that is where my loading proces keeps failing.
Best regards - Magnus
RE: Filament not loading to extruder
And also one last thing. I think i will just upgrade it fully to an mmu3, if there is no other good option. But here is the list over parts needed for the upgrade. How many of these things are strictly needed for the upgrade. It seems there are some of the things already in the mmu2s. But im not sure:
Idler
6x 5x16sh shaft
2x 5x6x25bt bushing tube
1x magnet (10x6x2 mm) (not purchaseable separately, part of this set of magnets)
1x coupler 5mm6x 625 bearing1x ball 7mm (ferromagnetic, zinc-coated)
2x blade
1x silicone stopper
Pulley and ELE:
If you have MK3S+, 1x MK3S+ MMU3 printer cable - Einsy
If you have MK3.5/S, 1x MK3.5/S MMU3 Printer Cable
5x collet5x PTFE tube 4x2.5x191x
MMU PD-board addon
Buffer:
10x PTFE 4x2.5x650
5x 693-2RS bearing
10x collet
5x 2.9x8.5 shaft
Fasteners as per package (spares included):
4x spring
11x M3x30 screw
32x M3x6 screw
28x M3nS screw
25x M3n nut
38x M3x10 screw
4x M3x18 screw
3x setscrew M4x5
Extruder parts:
1x PTFE 4x2.5x360
5x washer M3/3.2/9/0.8 A2
Prusa lubricant
Best regards - Magnus
And thank you in advance
RE: Filament not loading to extruder
Thank you very much for the advice. I will try out some of these things to see if they work.
I just have one question though: Why is it that when the filament reaches the extruder, the bondtech gears pulls it down, then pushes it up, then down again and then up again? Because that is where my loading proces keeps failing.
Best regards - Magnus
Hi Magnus,
I never questioned why the filament is juggled by the extruder...
Yesterday and the day before I had a problem with a friend's newly upgraded DIY MMU3
the final result was down to my friend pulling the filament out of the extruder, breaking the filament in the process.
this resulted in the filament aparrently feeding correctly then causing a filament out error, during the backfeed section of the process
it is likely that the failures that you are seeing, are due to the filament sensor adjustment. under normal conditions
the MMU3 uses all of the MMU2 hardware bearings, rods and bushes.
the Idler roller is re designed to be more robust and accurate rotation.
the selector becomes bi directional with the blades more firmly mounted,
new magnet and ball bearing improve the filament sensing
the new filament sensor assembly gives easier sensor adjustment.
as a first stage I would try a new selector print with twin blades, magnet and ball bearing, and all new large bore PTFE for filament feed, reverse bowden and short sections behind the selector plus the revised filament sensor tower and idler door...
I never recognised power issues with the MMU2, maybe I was lucky... as the PD Board and new cables were part of the upgrade I just fitted them as a matter of course.
One of the links I sent, mentions using MMU3 firmware on MMU2 hardware... you might wish too try that
Joan
I try to make safe suggestions,You should understand the context and ensure you are happy that they are safe before attempting to apply my suggestions, what you do, is YOUR responsibility.Location Halifax UK
RE:
Hi Magnus
For the Mk3S or Mk3S+ with MMU3 firmware
you need to download the Mk3s 3.14.1 firmware and MMU3 3.0.3 Firmware files. if I recall correctly (My friend's DIY MMU3 is using the 3.14.1 Revo vrsion of the firmware, because they have an e3D revo hot end,
Idler Print in PETG Files in MMU3 Printable parts on printables I Printed all of my parts
6x 5x16sh shaft Salvage mmu2 I think there are eight, five idler rollers, idler body end bearing and clam shell hinges
2x 5x6x25bt bushing tube Salvage MMU2
1x magnet (10x6x2 mm) (not purchaseable separately, part of this set of magnets) Possible Salvage from Mk3s old filament sensor
1x coupler 5mm6x 625 bearing1x ball 7mm (ferromagnetic, zinc-coated) May be in Mk3S spares bag check attraction to magnet
2x blade one in MMU2, one in MMU2 Spares bag
1x silicone stopper Works without this, but a bit noisyer
Pulley and ELE: 5 pulleys Salvage MMU2
If you have MK3S+, 1x MK3S+ MMU3 printer cable - Einsy Re use existing cables or use new cable and PD Board....
If you have MK3.5/S, 1x MK3.5/S MMU3 Printer Cable
5x collet5x PTFE tube 4x2.5x191x Difficult to source, my friend printed TPU Collets from printables or use modified part and 10mm pass through fittings as mentioned in post yesterday
MMU PD-board addon Ideally use PD Board and new cable
Buffer:I have had MMU1, MMU2 and MMU3, and never used a physical buffer I use Air Buffer (Spiling extra filament into the air...)
The MMU3 Buffer holds mor filament than the MMU2 buffer... so update if you intend to use a buffer
10x PTFE 4x2.5x650 I use 3mm ID Ptfe, Just bought 10 metres off Ali Express,
5x 693-2RS bearing Salvage MMU2 as far as I recall there are eight, 5 in the idler drum, one to support the end of the idler drum and two for the clam shell hinge
10x collet only required if using the buffr
5x 2.9x8.5 shaft only required if doing buffr
Fasteners as per package (spares included):
4x spring Salvage from MMU2 don't recall another two???
11x M3x30 screw General Spares or may be recovered from MMU
32x M3x6 screw Buffer?
28x M3nS screw ?Buffer
25x M3n nut ?Buffer
38x M3x10 screw Recover from MMU2
4x M3x18 screw Recover from MMU2
3x setscrew M4x5 New
Extruder parts: Print from MMU3 Mk3 spcific parts list on Printables
1x PTFE 4x2.5x360 If you buy 10 metres of tubing you should have enough for this
5x washer M3/3.2/9/0.8 A2 not sure where these go... mind getting old... lol! (Two on top of idler clamshell tension springs)
Prusa lubricant you should have some lube, only a smear needed on the selector rods
Hope this helps,
Joan
I try to make safe suggestions,You should understand the context and ensure you are happy that they are safe before attempting to apply my suggestions, what you do, is YOUR responsibility.Location Halifax UK
RE: Filament not loading to extruder
Thank you very much Joan
I will try this and see if it will work
RE: Filament not loading to extruder
G|ood luck...
I have a Mk4, arriving on Monday, with luck...
Need to find an MMU for that.
Joan
I try to make safe suggestions,You should understand the context and ensure you are happy that they are safe before attempting to apply my suggestions, what you do, is YOUR responsibility.Location Halifax UK