Compact MMU3 Buffer (with optional dry-box)

Overview

I love printing with the MMU3, but I don't like having to load and unload filament from the buffer back to my dry box when I'm not actively printing.

I wanted to make a new buffer than took up less space than the original, and could offer some protection to the buffered filament when it wasn't active. It should also offer some protection to all filaments loaded when the printer was not printing.

This is the result. A repurposed dry goods container fitted with a mating body that accepts the standard filament feed assemblies which clip in and allow each loaded filament to be buffered without interference from the container or other buffered filaments. 

The unit is intended to be placed upright so that filament hangs vertically so any interference with the walls is minimized.

Space is provided to include a desiccant dry-box at the bottom of the container if desired.

Bill of Materials:

• 1x Systema Ultra 4L food storage container (Manufacturers Link) (4L, 154mm  x 272mm x 142mm) (or equivalent). (The width and height are important as this allows the looped buffered filament to hang without interference)

• 6x M3 x 10mm  Cap socket machine screws (buffer body to buffer body fixing plate, either side of the food storage container lid)

• 6x M3 square nuts (buffer body to buffer body fixing plate)

• 6x M3 x 8mm, cap socket machine screws (dry box lid to dry box  body) (optional)

• 6x M3 square nuts (buffer body to buffer body fixing plate)

• 6x 297mm x 210mm plastic sheets (A4 Folio slip covers are perfect) (Filament separator sheets)

• Super glue (Fixing the dry box feet to the bottom of the dry box, to allow air circulation) (optional)

• Desiccant beads (for the dry-box) (optional)

• ~1.1m x 1.75mm filament in total (To stitch the filament separator plates in place), (broken down as follows)

  • 3x ~120mm x 1.75mm (To secure separator sheets to lower plate)

  • 4x ~120mm x 1.75mm (To hold separator plates apart via enforcers)

  • 2x ~120mm x 1.75mm  (To secure the separator sheets  inside the buffer body so they hang inside the container)

Tools Needed:

• Dremel with circular diamond cutting saw (or equivalent tool, for cutting the lid of the food storage container lid),

• Drill and 3mm drill bit (for drilling holes in the food storage container lid),

• 1x 2.5mm Allen key (The one you used extensively putting your MMU3 together)

• Scissors,

• Sharp side cutters,

• Ruler and straight edge,

• Craft knife,

• Fine tip permanent marker pen,

• Adhesive tape.

Assembly:

1. Purchase all items needed (or equivalent alternatives) as per the bill of materials.

2. Print all parts as per the project files or the included GCode.

Pro Tip:

If you print the dry-box in PETG you could potentially recharge the desiccant beads in place (PETG has a glass transition temperature of 80-85 degrees Celsius, compared to PLA which is 55 to 60 degrees Celsius). 

Prusa has filament drying times and temperatures here

Buffer Body & Fixing Plate

1. Using buffer body fixing plate as a stencil, place it on the lid of dry storage container and use a fine permanent marker pen to trace the inside slots for the individual buffer cartridges and the holes to hold it to the main buffer body. Make sure you locate it centrally.

2. Using the Dremel, cut the internal hold in the lid, cut the hole as once piece, there is no need to maintain individual holes for the 5 cartridges.

3. Use a 3mm drill bit, drill out the holes for the screws in the storage container lid.

4. Insert M3 square nuts into the main buffer body.

5. Check the lid for interference for the cartridges or the filament separators.

6. Fix the buffer body and fixing plate together with the lid of the container sandwiched between. Don't over tighten screws unnecessarily.

Result

• The buffer body should now be fixed to the lid of the storage container

• The edges of the hole cut in the lid of the storage container should not interfere with the buffer spools or filament separator sheets,

Marking & Cutting Filament Separator Sheets

1.  Take the separator plate template and tape the two pieces together.

2. Use the whole separator plate template to mark out six plastic sheets using the fine marker pen. Trace the outline and the holes.

3. Using a craft knife and ruler, cut out each sheet. Using the same knife cut a small vertical slit over the top of each hole (so you can push the fixing filament though).

Result

• You should have six identical separator sheets ready to install.

• All nine holes marked should have sits cut across them to allow you to push fixing filament through easily.

Installing Filament Separator Sheets

There are six separator sheets to match the five buffer slots between them.

• Four inner separators that keep the filament separated from each buffer slot, these are inserted though the fixing plate into the buffer body.

• Two outer separators that guide filament from buffer 1 and 5  so they cannot get tangled inside the storage container.

• Separator sheets are installed in order from 1 to 6  such that "outer 1  | inner (x4) | outer 2". Doing this makes it easier to feed the fixing filament  in from one direction.

Pro Tip:

Cut the fixing filament at a sharp angle so it makes it easier to thread through separator sheets.

Outer Sheet 1

1. Outer separators ARE NOT fixed to the buffer body, but instead 'flare out'.

2. Position one filament separator sheet into the lower filament separator fixing plate (That hangs in the bottom of the storage container) (it has three filament fixing holes to match the three holes at the bottom of each sheet). The sheet is positioned in the the first buffer slot. (Not in one of the four narrow slits reserved for the inner sheets).

3. Fix the sheet in place by passing a length of 1.75mm filament through each of the three guide holes so it secures the sheet in place. Advance each fixing filament so it just passes into the guide hole for the first narrow slit (between buffer slot  1 and 2).

Inner Sheet 1

1. Inner separators ARE fixed into the buffer body.

2. Position one sheet into the buffer body (and fixing plate) into the narrow slit between buffer slots 1 and 2.

3. Fix the sheet in place by passing a length of 1.75mm filament through each of the two guide holes so it secures the sheet in place inside the buffer body. Advance the fixing filament so it just passes into the guide hole for the second narrow slit (between buffer 2 and 3).

4. Position the bottom end of the sheet into the narrow slit between buffer 1 and 2 and push the three fixing filaments to the next guide hole for the next sheet.

Inner Sheet 2

1. Position the next sheet into the buffer body (and fixing plate) into the narrow slit between buffer slots 2 and 3.

2. Fix the sheet in place by advancing each fixing filament forward so they secure the sheet in place inside the buffer body. Push the fixing filaments so they just pass into the guide hole for the next narrow slit (between buffer 3 and 4).

3. Position the bottom end of the sheet into the narrow slit between buffer 2 and 3 and push the three fixing filaments to the next guide hole for the next sheet.

Inner Sheet 3

1. Position the next sheet into the buffer body (and fixing plate) into the narrow slit between buffer slots 3 and 4.

2. Fix the sheet in place by advancing each fixing filament forward so they secure the sheet in place inside the buffer body. Push the fixing filaments so they just pass into the guide hole for the next narrow slit (between buffer 4 and 5).

3. Position the bottom end of the sheet into the narrow slit between buffer 3 and 4 and push the three fixing filaments to the next guide hole for the next sheet.

Inner Sheet 4

1. Position the next sheet into the buffer body (and fixing plate) into the narrow slit between buffer slots 4 and 5.

2. Fix the sheet in place by advancing each fixing filament forward so they secure the sheet in place inside the buffer body. Push the fixing filaments forward so they exit the buffer body.

3. Position the bottom end of the sheet into the narrow slit between buffer 4 and 5 and push the three fixing filaments about half way to the final guide hole.

Outer Sheet 2

1. Outer separators ARE NOT fixed to the buffer body, but instead 'flare out'.

2. Position one filament separator sheet into the lower filament separator fixing plate The sheet is located in the the fifth buffer slot. (Not in one of the 4 narrow slits for the inner sheets).

3. Fix the sheet in place by pushing the filament through each of the three final guide holes so it secures the sheet in place. Advance the fixing filaments so they pass just outside the fixing plate.

Result

• All inner filament separator sheets should be fixed inside the buffer body, with the two outer sheets flaring out on each side.

• All separator sheets should be fixed to the lower separator fixing plate, the four inner sheets into the four thin slits between buffer slots and the two outer sheets into the corresponding outer buffer slot.

• Fixing filaments in the buffer body should pass though all inner sheets.

• Fixing filaments in the lower fixing plate should pass though all sheets (inner and outer).

• Fixing filaments should extend 2-3 mm outside the buffer body and fixing plate.

Render showing placement of the four inner separator sheets in the lower fixing plate

Render showing placement of the two outer and four inner separator sheets in the lower fixing plate

Render showing what the assembly looks like with the four inner separator sheets installed. Note: Outer sheets not shown, but these would be present and flare outwards from the uppermost enforcers as they are not fixed in the buffer body.

Installing Filament Separator Enforcers

Enforcers are provided to ensure that separator sheets are held apart so each filament is free too move unrestricted within a similar volume.

• There are four separator sheet enforcers

• The install procedure is the same for each.

• Each separator sheet is fixed into each enforcer

1. Take a separation enforcer and position the first outer sheet into the outer-most fixing slot.

2. Push a length of fixing filament through the guide hole on the outer-most side so it passes through the guide and the separator sheet into the  next guide.

3. Position the next separator sheet into the next fixing slot and advance the fixing filament through to the next guide.

4. Repeat for all separator sheets, the final sheet should be the second outer separator sheet.

5. Repeat for the remaining separator enforcers.

Result

• All separator sheets should be held in place by the four separator enforcers.

• The gap between sheets should be consistent and the volume of each buffer slot created should be similar.

Render showing placement of the four inner separator sheets in one of the separator sheet enforcers

Dry-box assembly (Optional)

While the compact MMU3 buffer dry-box is not meant to airtight (the buffer spools have airgaps), filament held within it is significantly less exposed to natural air currents compared to the buffer provided with the MMU3 by default. However I have included a small desiccant container that fits at the bottom of the container and doesn't interfere with the filament buffering if you think you need it.

1. Insert four M3 square nuts into the dry-box body.

2. Fill the body with silica desiccant beads.

3. Place the lid of the dry-box over the body and use four M3 machine screws to fix it in place.

4. Flip the dry-box over and use a dab of super glue to fix each of the six feet to the bottom of the dry-box.

Result

The dry-box is assembled and filled ready to go.

Final assembly

1. Place the dry-box in the bottom of the storage container.

2. Place the lid (with buffer body, fixing plate, separators and enforcers into the container.

3. Secure the lid to the body of the container.

4. Prepare a buffer wheel assembly by loading filament into it  (with some buffered) and then lower into into one of the buffer body slots. Click it into place.

5. Repeat for the remaining buffer wheel assemblies.

6. Connect to the output PTFE tubes from the buffer wheel assemblies to the input of the MMU3.

Result

The compact MMU3 buffer is in place and ready to go.