**UPDATED** Integrated Spool Holder + Buffer for Core ONE & MMU3 MKII

Tired of managing messy filament tubes and bulky buffers? Here’s a sleek, all-in-one solution built for your MMU3

A compact filament management solution for multi-material printing.

I needed a space-saving alternative to the stock Prusa buffer for my Core ONE + MMU3 setup—so I designed this integrated unit that combines a spool holder and buffer into one clean, functional part.

This prints in one piece (or two, depending on your machine) and fits comfortably on a Core ONE bed. MK4 users, don’t worry—there’s a trimmed version for your 210mm Y-axis too!

🔧 Why I Designed This

After years of struggling with inferior buffer solutions, I had enough!  I took an evening and solved the issues that are prevalent with all of the buffers I've used and  researched.  My criteria were:

Compact and didn’t hog desk space

Integrated—no separate buffer

Easy to print and assemble

Worry-Free - must be 100% reliable

So I made this: a minimalist, reliable combo that fits perfectly on the Core ONE bed (and trimmed versions fit MK4.)

✅ Features

🔧 All-in-One: Spool holder + buffer combined in one footprint

🧵 Perfect for MMU3 setups

📏 Fits Core ONE (220mm Y) or trimmed for MK4 & others (210mm Y)

🔄 Mirroring supported: Flip it for left/right configurations

🧩 Who It’s For

Core ONE and Prusa MK4 users running MMU3

Makers who want a tidier, space-saving solution

Anyone replacing the Prusa buffer with something smarter

🔁 How It Works

 I took all the unnecessary parts of a spool holder, and all the unnecessary parts of a buffer and fed them to the shredder.  This is the bare minimum hardware (and best solution) to fully manage your Prusa MMU buffer needs.

🧪 Filament Compatibility

Tested and working with:

PETG

PLA (non-brittle types)

TPU (Shore 90)

ASA

BASICALLY ANY FILAMENT!

🧰 Parts Needed

Print:

1x Spool Holder

1x Buffer

Other:

1x Prusa Buffer Cartridge
Note: Assembled version required. See Prusa Guide for details.

5x M3x6mm screws

2x M3x10mm screws

1x 125mm PTFE tube

🔧 Assembly

Attach buffer to spool holder using:

5x M3x6 screws (counterbored buffer side)

2x M3x10 screws (spool holder side)

Insert 125mm PTFE tube into one side of buffer cartridge.

Connect MMU-bound PTFE tube to the other side.

Mount spool so filament exits the top.

Feed filament through short PTFE segment, around the wheel, and out to the MMU

🌀 Filament Pathway

Filament exits top of spool

Feeds into short PTFE → loops around buffer

Exits through long PTFE to your MMU

Upon unload, up to 750mm of filament retracts cleanly into the buffer’s internal cavity

💬 Share & Collaborate

Got ideas for upgrades or mods? Want to share your build?

➡ Drop a comment with your thoughts
➡ Post a make to show your setup
 

Support my work.  It will always be free, but show some love if you are so inclined.