Buffer for Prusa MMU

Disclaimer: This model is designed to be used with another model, the SpoolBox, which is available for purchase, or alternatively through MyClub.

The Buffer

This module will add an extra feature that has been requested: a buffer to bypass the original Prusa buffer.

I must confess that I tried some alternatives to the Prusa system; however, this one seems to work best with the MMU3 (I have no way to test previous versions).

Thus, this buffer, external to the SpoolBox (more on this option later), operates similarly to the original Prusa cassette system. So, what is the advantage?

• This version is more compact;
• The number of operations to change the filament is reduced; 
  • To change the filament, simply retract the material from the Spool, place a new spool, insert the guide piece, and pull the filament up to the MMU.

I took care to design something that does not require modifications to the SpoolBox you may have already produced; just connect it and it is ready to use.

There is a new version of the guide (Pulley and Guide V2.3mf) that should attach to the structure without the need to hold it by hand. It works like a spring; you just need to press it slightly to insert it into the slot, and the elastic effect of the PETG (the material it should be printed from) will do the rest. 

If, for some reason, the guide does not have enough strength for a good attachment, slightly force the guide outward to increase its diameter, that should work.

Why didn’t I place the buffer inside the SpoolBox? The reason is simple: the area needed to accommodate filament retraction is larger than the entire internal area of the SpoolBox... Considering that the SpoolBox already occupies the entire print area of the PRUSA Mk series, I couldn't increase the print bed size, and I also didn't want to further subdivide the SpoolBox. Therefore, I opted for the obvious solution: pulling the buffer outside the box.

PS: The guide, the orange part with a U shape, will me updated to stay in place without the necessity to secure it with your hand.

you can find does nice tags you see on the video here: Tags for MMU PTFE tubes

Problems that can arise when inserting the filament 

In certain situations, especially with cheaper pneumatic adapters, it can happen that the filament can jam at the adapter entrance. This is well known situation and also occurs with some adapters used by PRUSA and other brands, and it's due to the abrupt reduction in diameter at the adapter entrance, which should be conical but is not. To address this, there are some solutions that can help, as well as a more efficient and definitive solution:

1. Try cutting the tip of the filament on three or four sides to make it like the tip of a pencil, but not sharp. Additionally, the filament should have its end as straight as possible since the spool makes the filament curved.
2. Use a newer adapter like the Festo QSM-M6-6 (it can be found on amazon too), which was tested by FrankVZ and recommended by me, this one or a very similar is also used in the Prusa hotend along with the MMU3 kit, and precisely to avoid these situations at the filament entrance.

Assembly

Printable parts

All print files can be found on the folder “Buffer”. Their you will find:

• Cassette Bottom.3mf
• Cassette Top.3mf
• Pulley and Guide.3mf
• Base for Box and Buffer.3mf

If you take a look at the image bellow, you  will understand that there is no need to show the logo on the buffer side, so, I've made special parts for that side without the logo, you will find them under the project “SpoolBox with Buffer for Prusa MMU”, under the file folder “Buffer".

• Base_Right_withoutLogo.3mf
• Top_Right_Translucent_PETG_NoHexagons.3mf

Print this parts using PTFE; I've use PRUSAMENT: 

• Galaxy Black PETG;
• Orange PETG;
• Orange Transparent PETG.

The result of this color / material combination:

Other Parts

• 6x CHC (DIN 912  A2-70) bolts and nuts - M3x8mm
• 1x Bearing - MR128 (D=12 d=8 L=3.5 [mm]) Links to (Amazon) or (Bambu Lab)
• 2x Pneumatic Accessories to connect the PTFE tube

Assembling all the parts.

Change Log

• (22-06-2024) - Initial release
• (24-06-2024) - Updates do the "Base for Box and Buffer.3mf" added pocket to insert TPU feet's
  • The guide now functions as a spring, thus it should stay in place without the need to hold it by hand while the filament is being inserted. Initially, I will maintain the original version "Pulley and Guide.3mf" However, once members confirm that "Pulley and Guide V2.3mf" is a better solution, I will remove the initial version in favor of V2.