MMU Filament Buffer (approx 400-500mm)

Universal MMU Filament Buffer

This is a universal MMU buffer that stores approx. 40 -50 cm of filament in an enclosed housing. The filament is protected from dust and stays dry noticeably longer, even if you leave it in the buffer between prints.

Hardware required

• 2× 608-2Z ball bearings (8 × 22 × 7 mm)

• 8× neodymium magnets, Ø4 × 2 mm

• 16× M3 heat-set inserts (per buffer; when stacking, 6 fewer for each additional buffer

• 14× M3 × 8 mm countersunk screws (per buffer; when stacking, 6 fewer for each additional buffer

• 2× M3 × 12 mm countersunk screws

• 2× PTFE tube (4 mm OD / 2 mm ID), approx. 20 mm long

• Super glue (CA)

Optional (one of the following):

• 2× ECAS04 couplings, or

• 2× PC4-M10 push-fit fittings

Printed parts
Tray_Front_ECAS.step, (or Tray_Front_M10.1x1.step, or Tray_Front_M10.2x1.step), Tray_Bottom.step, Filler_Top_Lid.step, Buffer_Top_Lid.step, Filler_Base.step, Buffer_Base.step, Handle.step, Tray_Top.step, Wheel_Top.step, Axle.step

Printing

• Orientation as shown in the pictures. (Material, layer height, infill, supports see print settings)

• Choose the front panel that matches your coupling. There are two versions for PC4-M10 fittings. In my case, "Tray_Front_M10.2x1" works best: the M10×1 thread is enlarged by 0.1 mm so the fittings screw in easily.

• Buffer_Top_Lid has holes closed by a thin sacrificial layer. You can use them to mount cereal containers (as used for filament dry boxes). Drill them open before assembly if needed.

• Buffer_Base has the same kind of holes for brackets, so you can mount the buffer (with or without a cereal container) to 2020 or 3030 aluminium extrusion.

• The lid mounting holes are through-holes, so you can stack several buffers and screw them together. Use M3 screws long enough for your stack (each buffer is 25.6 mm high).

Print settings

• Material: I use ABS, but PLA or PETG will work as well

• Walls: 4

• Infill: 30 %

• Layer height: 0.2 mm

• Line width: 0.45 mm

• Supports: none

• Orientation as shown in the pictures

Assembly

1. Install all heat-set inserts first.
   ⚠ Stacking multiple buffers: The six inserts around the edge of Buffer_Base (marked in red in the picture) hold Buffer_Top_Lid. If you want to stack buffers, install these six inserts only in the bottom buffer of the stack. In all other buffers, leave these holes empty so the long screws can pass through into the bottom buffer. Install all other inserts as usual.

2. Press the ball bearings into the two wheel halves.

3. Press the wheel halves together and secure them with a drop of glue.

4. Press the axle through both bearings.

5. Note: one side of the wheel is marked "TOP". This side must face up.

6. Screw the wheel assembly (wheel, bearings, axle) to Tray_Bottom.

7. Screw Tray_Top to Tray_Bottom and to the axle. Check that the wheel turns freely without rubbing.

8. Screw Tray_Bottom, Tray_Front and Handle together using the two M3 × 12 mm screws.

9. Press the two short PTFE pieces into Tray_Bottom from the back. They guide the filament when you insert it.

10. Glue four magnets into the front panel, all facing the same way.

11. Glue the remaining four magnets into Buffer_Base, oriented so they attract the front panel magnets and do not repel them.

12. Press or screw the ECAS or PC4 fittings into the front panel.

13. Screw Filler_Top_Lid into Buffer_Top_Lid. Depending on your printer, this can be a tight fit and may need some light trimming.

14. Screw Filler_Base into Buffer_Base.

15. Screw Buffer_Top_Lid and Buffer_Base together and slide the drawer into the housing.

⚠ Both fillers must sit completely flat in their housing parts. Otherwise there won't be enough room for the filament. Gluing them in can help.

How it works

Pull out the drawer. Feed the filament through the inlet fitting, over the wheel, and out through the outlet on the other side. Then slide the drawer back in.

During normal printing, the filament simply runs over the wheel. When the MMU unloads or retracts filament, the excess is pushed back into the buffer, where it can form a loop without twisting or kinking. The next time that filament is used, the loop is pulled out of the buffer first until the filament rests on the wheel again, and printing continues as normal.

Tested with:  PICO MMU --> https://github.com/lhndo/LH-Stinger/wiki/Pico-MMU