Prusa Mk4/MMU3 & Mk3S/ MMU2S Tower Print Buffer

August 20, 2024:  Re-uploaded the unique MK4 parts as the original upload appear to be corrupt.

This Tower Print Buffer has been updated to work with the MK4 and MMU3 system (It still works with the Mk3 and MMU2 as well).  The frame mounted supports are tweaked for reasonable clearance to the print head, the cross bar between the spool supports gives better clearance to the MMU3 to MK4 Print Head feed tube and better guidance for a tall print, The center roller supports have guide fingers that prevent the feed tube from hanging up when the print head descends toward the print bed from a high position, and the roller carrier plate openings are tweaked for improved spool clearance.

The remaining parts and hardware remain the same along with the assembly below.  Note, only model files (.AMF) are uploaded, no g-code uploaded for the upgrade.

This is a redesign of the MMU2S Print buffer system to relocate the 5 spools above the printer and a rear mounted vertical buffer system. It saves a lot of space, fitting within a 56cm X 56cm (22" X 22") footprint. It just fits inside an IKEA Lack enclosure that is double stacked (except the Mk3S control panel sticks out a little).

It is also far easier to feed new filament. The MMU2S feed tubes are shortened to under 10CM and there is more space for fingers to feed filament to the MMU2S rollers. The feed from the spools is also relatively easy with a large space for hands to get in and work.

This solution has been tested with PLA, ABS, and PETG. TPU also works.  Any 1.75mm dia material that can be curled into a 9cm (3.5") diameter circle should work.

Print instructions

Prusa MK4/MMU3 & Mk3S/MMU2S Tower Buffer Assembly Instructions

Non printed parts list:
M3 Square Nut 5.2 X 5.2 Square x 1.75mm Thick 44
M3 Hex Nut Standard M3 Hex Nut 29
M3 X 12 SHCS Standard M3 Socket Head Cap Screw 69

Prusa MMU2S Re-used parts:
8x22 Ball Bearing (Skateboard Bearing) 20
Spool Roller Tube 8MM OD Aluminum Tube (shorten) 10
Filament Guide Tubing 2mm ID X 4mm OD Teflon Tube 3m

1) Download the print files (Ready to print MMU2S single color G code and STL files for altering print setup are provided). Note: The G code files are set up to print with PETG material.

2) Procure the commercial hardware from the parts list, M3 screws, square nuts, hex nuts, and 4mm OD x 2mm ID Teflon tubing (or re-use the existing buffer tubing).

3) Cut the existing 10 aluminum buffer roller tubes to 10.5cm (4.25”) long.

4) Extract and open the parts lists, 3D print parts, and commercial hardware.

5) Print all the components. Note, a few are quite large and will take more than a day to print!

6) Cut the Teflon tubing to length for the spool feeder section. Cut them a couple of cm longer than the lengths listed below and trim them to appropriate lengths during assembly.
a. One Center tube (Spool 3): 36cm (14”)
b. Two inside tubes (Spools 2 & 4): 41cm (16”)
c. Two outside tubes (Spools 1 & 5): 46cm (18”)
d. Five MMU2S Feeder Tubes: 9cm (3-1/2”)

7) Remove the old print buffer assembly and tubes. Keep the spool roller bars and bearings.

8) Install the five short MMU2S Feeder tubes into the MMU2S input side.

9) Assembly:
a. Install 4 square nuts into the main spool support legs then
snap them in place. Note that the raised features are
oriented to the center of the printer (toward the MMU2S
Unit).
b. Install 6 square nuts and 6 hex nuts in each spool support
block. Note that 2 square nut slots are not used on each
block, and that the nuts are installed to make a mirrored
assembly. Do not install square nuts on the front-outside
screw holes (they are not used). Use 4 screws to fasten each
spool support block to the legs.
c. Using 4 screws, attach the front spacer bar to the spool
support blocks.
d. Using 12 screws, attach the six spool roller guides to the
spool support blocks. Note that there are left and right pairs.
Insert the aluminum roller tubes in the bearings and snap a
pair into each roller guide set.
e. Using 8 screws, attach the two filament guide spacer blocks
to the spool support blocks (on the backside of the printer).
f. Install 4 hex nuts in each filament guide support block, then
install the support blocks onto the filament guide spacer
blocks with 8 screws.
g. Install 5 hex nuts into the middle filament guide block.
Loosely install the filament guide tube clamp screw. Install 3
square nuts into each of the 4 bottom filament guide blocks.
Loosely install one filament clamp screw into each of the
bottom guide blocks. Attach the bottom filament guide
blocks to the middle filament guide block.
h. Snap the top half of the buffer tower to the bottom half and
install it under the rear cross bar of the printer base. Snap
the middle guide block into the top of the buffer tower.
i. Attach the middle guide block assembly onto the filament
guide support blocks using 4 screws.
j. Install 2 square nuts and 1 hex nut into each of the curved
filament guide blocks. Loosely install a filament guide clamp
screw into each block. Install the smaller of the 4 blocks on
the spool 2 & 4 area of the filament guide block using 2
screws each. Install the larger of the curved blocks on the
spool 1 & 5 (outside) locations using 2 screws each.
k. Install the 36cm (14”) long Teflon tube into the middle (spool
3) guide block. Ensure it extends all the way down to the top
edge of the tower opening and rests just inside. Tighten the
clamp screw such that the tube cannot be easily pulled out
and a piece of filament still slides easily through it. Repeat
the installation of tubes with the next longest pieces in spool
locations 2 & 4, then the longest 2 sections in spools 1 & 5.
Ensure all the tubes sit about 1CM (1/2”) below the top edge
of the tower lip. Use your finger to push the tubes forward.
They must be able to clear the front edge of the tower and
protrude out toward the MMU2S unit. Once satisfactorily
installed, trim the portion of the tubes that point toward the
filament spools about 5cm (2”) away from the filament guide
blocks.
l. Trim the MMU2S tubes to be about 3cm (1.25”) from the
surface of the buffer tower. These can be adjusted a little
further away for better finger clearance if soft printing
materials (TPU) will not be used. Trimming too far back can
cause the filament to hang up and not slide down into the
buffer reliably.
m. Check and tighten all the screws, center the MMU2S unit
input on the buffer slots, and the assembly is ready to go!

Setup tips:

1) When loading spools, ensure the filament feeds from the bottom of the spool (closest to the top of the printer). Feeding from the top of the spool can cause the spool to be pulled off the rack.

2) The shortened MMU2S feed tubes appear to work best at about 25mm (1") from the buffer. Increasing the gap improves the ease of loading the tubes from the buffer side so some experimentation may be needed to optimize this.

3) Use the Mk3S filament load function. Feeding filament into the stock tube receptacles can be a be a problem when the filament cannot push beyond the end of the tube. Cut the filament at a diagonal and try different diagonal cut positions until you find the best angle for trouble free feeding.