Why another Filament Buffering Solution?
I wanted a solution that met the following requirements:
- Does a decent job of handling retracting filament (duh)
- Fully 3d printable while ideally using a minimal amount of filament
- Retains maximum visibility of filament in the system
- Easy to change filament
The openscad source for this project is available under the MIT license at https://github.com/x0pherl/Filament-Bank
This is a filament buffering system designed for use with the Prusa MMU2s, but should be easily adaptable to suit similar requirements or MMU2S modifications adding additonal filaments.
The original inspiration for this comes from David Shealey's brilliant design for his Prusa MMU2 Filament Retract Bank. His concept of a simple wheel releasing filament into a channel was the first workable buffering system for the MMU2S, as far as I'm concerned. However, this design suffers from two flaws. First, the walls of the chambers were designed to be acrylic plastic -- which had the advantage of being clear, but required some knowlege of working with acrylic.
This led Piotr Karkovski to create a modified Fully printable Prusa MMU2 Filament Retract Bank (Buffer). This solved the orignial issue, and Piotr's instructions suggested maintaining visibility by using hex infill with no top or bottom layers. This was a very nice innovation, but it didn't help to solve the other issue with Shealey's original design.
Shealy's design relies on a paddle that slides up and down that, as you feed filament in, is supposed to force the filament to return up the other side. While this occasionally worked for me, I found it to be frustating in practice. Garth Gangaway set out to solve this problem with a new design, but this again relied on acrylic panels, and I did not like the clipping solution used on this model.
I am super grateful to all of these designers and their innovation. While I haven't used their original designs in creating this project, it certainly wouldn't exist without their original work, especially David Shealey's original design.
Complete printing recommendations are available in the github readme: https://github.com/x0pherl/Filament-Bank#step-one-printing-guide
for the sidewalls and separator walls, I recommend printing these with transparent filament to allow more visibility to the filament chambers. Printing these with standard settings will create a sturdier chamber, but I recommend printing them with 10% hex infill with no top/bottom layers. This will allow maximum visibility into the buffer chambers.
for most of the parts of the frame, I recommend printing this with transparent filament and minimal infill (downloadable gcodes are 5% hexagonal infill).
it may be better to read this from the github repo at https://github.com/x0pherl/Filament-Bank#assembly (that version will be updated over time, this is likely to remain static)
Buffering Chamber Assembly
Start with the bottom bracket. It may be helpful to use a utility knife to clean any printing artifacts out of the 6 slots along the bracket. Note that on the one side, next the round hole for the peg, there is a small notch. That side is the "deeper" section, and your seperator walls should be aligned to match.
Slide each of the six separator walls into the slots on the bottom bracket. With the notch on the right of the bottom bracket, slide in the two shorter pegs, then use a pair of pliers to give each peg a twist or two clockwise to lock the pegs in place.
Then carefully align one of the sidewalls with the separator walls, and slide it down into the bottom bracket until it is firmly in place. Repeat with the other side.
Align the top bracket with the sidewall and separator walls and slide into place. With the back bracket facing to the right, slide in the two longer pegs, then use a pair of pliers to give each peg a twist or two clockwise to lock the pegs in place.
Congratulations, you've finished the buffering chambers! Why don't you reward yourself with some gummi bears :)
Wheel Bracket Assembly
First, fit one of the printed axles through the top filament wheel mount (when inserted properly, it will sit flush on the plate). Place this on a flat surface so that the axle is pointing upwards.
Now, push one of the bearings into a the center of a wheel. Push the combined wheel/bearing onto the axle which is facing upwards.
Carefully align the bottom filament wheel mount so that the socket for the axle aligns with the axle, then carefully pick up the assembled bracket and gently turn the axle a bit by hand or using a coin to turn it. TIGHTEN VERY GENTLY, or the axle may break.
IF the axle breaks, you will need to get the remaining part out of the bottom bracket. Using a utility knife and stabbing the center of the broken axle and turning it is effective in this case.
Once you have the axle in place, insert the two 3d printed connector bolts to hold the top and bottom brackets in place. When all of the screws are in place, make sure they are all flush with the bottom bracket, or the brackets will not all fit into the buffering chamber.
Finally, make sure the wheel spins freely. You may need to carefully push the wheel towards the top or bottom bracket to eliminate friction and allow it to freely turn.
Screw two of the two PTFE tube quick releases into the top of the bracket, and you'll have assembled a wheel bracket.
Repeat 4 more times and then reward yourself with some gummi bears.
The top bracket of the buffering chamber has brackets for hanging. Using M3 screws, secure the buffering chamber to a wall or your print stand. Ideally, there should be a short line of travel from the MMU2s unit downward to the buffering chamber.
Insert each of the wheel assemblies into the top bracket. Note that the back should be angled down as you insert them, so that the guide along the back lines up with the protrusion along the back of the top bracket. Then drop the front of the wheel assembly down and secure it with one of the thumb pegs. If you printed the pegs and wheels in five different colors as suggested in the printing instructions, be sure to match them up.
Finally insert ptfe tubing from the back of the wheel assemblies, and run that to your MMU2s unit; and run PTFE tubing from the front of the wheel assemblies to your filament stands.
Now you're ready to print!
Part One - Filament Buffer Assembly
Part Two -- Wheel Bracket Assembly
Part Three -- Final Assembly