Prusa Mk4/MMU3 & Mk3S/ MMU2S Tower Print Buffer

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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 instructionsPrusa MK4/MMU3 & Mk3S/MMU2S Tower Buffer Assembly InstructionsNon printed parts list:M3 Square Nut 5.2 X 5.2 Square x 1.75mm Thick 44M3 Hex Nut Standard M3 Hex Nut 29M3 X 12 SHCS Standard M3 Socket Head Cap Screw 69Prusa MMU2S Re-used parts:8x22 Ball Bearing (Skateboard Bearing) 20Spool Roller Tube 8MM OD Aluminum Tube (shorten) 10Filament Guide Tubing 2mm ID X 4mm OD Teflon Tube 3m1) 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 thensnap them in place. Note that the raised features areoriented to the center of the printer (toward the MMU2SUnit).b. Install 6 square nuts and 6 hex nuts in each spool supportblock. Note that 2 square nut slots are not used on eachblock, and that the nuts are installed to make a mirroredassembly. Do not install square nuts on the front-outsidescrew holes (they are not used). Use 4 screws to fasten eachspool support block to the legs.c. Using 4 screws, attach the front spacer bar to the spoolsupport blocks.d. Using 12 screws, attach the six spool roller guides to thespool support blocks. Note that there are left and right pairs.Insert the aluminum roller tubes in the bearings and snap apair into each roller guide set.e. Using 8 screws, attach the two filament guide spacer blocksto the spool support blocks (on the backside of the printer).f. Install 4 hex nuts in each filament guide support block, theninstall the support blocks onto the filament guide spacerblocks with 8 screws.g. Install 5 hex nuts into the middle filament guide block.Loosely install the filament guide tube clamp screw. Install 3square nuts into each of the 4 bottom filament guide blocks.Loosely install one filament clamp screw into each of thebottom guide blocks. Attach the bottom filament guideblocks to the middle filament guide block.h. Snap the top half of the buffer tower to the bottom half andinstall it under the rear cross bar of the printer base. Snapthe middle guide block into the top of the buffer tower.i. Attach the middle guide block assembly onto the filamentguide support blocks using 4 screws.j. Install 2 square nuts and 1 hex nut into each of the curvedfilament guide blocks. Loosely install a filament guide clampscrew into each block. Install the smaller of the 4 blocks onthe spool 2 & 4 area of the filament guide block using 2screws each. Install the larger of the curved blocks on thespool 1 & 5 (outside) locations using 2 screws each.k. Install the 36cm (14”) long Teflon tube into the middle (spool3) guide block. Ensure it extends all the way down to the topedge of the tower opening and rests just inside. Tighten theclamp screw such that the tube cannot be easily pulled outand a piece of filament still slides easily through it. Repeatthe installation of tubes with the next longest pieces in spoollocations 2 & 4, then the longest 2 sections in spools 1 & 5.Ensure all the tubes sit about 1CM (1/2”) below the top edgeof the tower lip. Use your finger to push the tubes forward.They must be able to clear the front edge of the tower andprotrude out toward the MMU2S unit. Once satisfactorilyinstalled, trim the portion of the tubes that point toward thefilament spools about 5cm (2”) away from the filament guideblocks.l. Trim the MMU2S tubes to be about 3cm (1.25”) from thesurface of the buffer tower. These can be adjusted a littlefurther away for better finger clearance if soft printingmaterials (TPU) will not be used. Trimming too far back cancause the filament to hang up and not slide down into thebuffer reliably.m. Check and tighten all the screws, center the MMU2S unitinput 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.