Prusa MMU3 Review

Introduction

I have finally upgraded to MMU3 last week. I upgraded my MK3S+ to MK3.9 almost a year ago, and I have been keeping an eye on multi-color/multi-material upgrade options since MMU2 but I was not fully convinced. I have finally decided a few weeks ago and I have purchased the MMU3 upgrade and installed it last weekend. This post is my early impressions about MMU3, and I will update it in the future if I change my mind on something I write now.

I am actually not a big fan of color prints, that is because I like printing functional parts. However, there are a few reasons I want to use a multi-material/color feature:

• color prints are much more interesting for kids

• different materials for supports can be used

• up to 5 filaments are always ready to be used, no need to manually change the filaments between prints

I have hesitated to install MMU upgrades until now because:

• I was not sure if it seamlessly works

• I was not sure if it affects single filament printing

I should mention that I mostly print with PLA, sometimes with PETG (or variants like NGEN) and rarely with FLEX.

I have purchased the MMU3 kit with the plastic parts as I am sure Prusa does a better job than me. The assembly of MMU3 upgrade kit is not very difficult. It takes some time but it is definitely much easier than building the printer. The installation does not involve fine tuning, only the position of (FINDA) filament sensor and the position of pulleys have to be adjusted and these are very simple and also can be (probably must be) adjusted also later.

How MMU3 Works

MMU3 unit consists of the following:

• a buffer with five removable cartridges
• five pulleys in the MMU3 unit
• idler in the MMU3 unit
• selector in the MMU3 unit

Below MMU3 unit is shown:

The buffer is a separate assembly usually stays next to the printer:

Each filament (spool) is connected to a cartridge in the buffer with a long (65cm) PTFE tube (yellow arrows in the photo above). I am told that this PTFE tube should not be longer or shorter, I believe the length is used in the firmware for optimum operation. Probably the same is true for all PTFE tubes.

The cartridge basically forms a loop, where one side is connected to the filament (described above, yellow arrow in the photo above), the other side is connected with another long (65cm) PTFE tube (red arrow in the photo above) to a pulley in the MMU3 unit. There are five cartridges in the buffer and there are five pulleys in the MMU3 unit, thus up to 5 filaments are supported. The filament has to be manually fed from the filament side to pulley side when the filament is being loaded. Thus, the cartridge has to be removed first. The buffer is needed because the filaments are retracted during operation when changing the filaments and the retracted filament stays here to prevent tangling.

The pulleys stay on a shaft connected to the pulley motor. Each pulley has gears to hold the filament. However, for this to work, the filament has to be slightly pushed down, and this is the job of the idler. The idler is also connected to the shaft of the idler motor, so it can rotate. The metal bearings on the idler can push the filament down on either none or one of the pulleys. Thus, either none of the pulleys are engaged or one is engaged thus it can pull or push the filament back or forward.

Naturally, the position of each pulley thus the filament is different. The selector moves in front of the selected filament to receive it (from the pulley) and guide it to the Nextruder. There is a FINDA filament sensor working together with a metal ball in the selector. The selector is connected to the Nextruder with another (36cm) PTFE tube.

The original Nextruder (idler, swivel, tension screws and gearbox main plate) is slightly modified to work together with MMU3.

First Prints

I experienced a few problems initially.

First, I had to re-adjust the position of one pulley, as it was not pulling the filament properly. This was very simple.

Second, there was a problem with one filament and I am still not sure what the problem was but I have ejected and reloaded the filament and then it worked fine. I was a bit puzzled with this issue but reloading the filament resolved it for good.

Third, and it seems this can always happen, depending on the shape of the filament, loading the filament can be sometimes difficult. Not very difficult but what I mean is it may not be seamless and requires some manual intervention. The manual describes loading steps as “push the filament until it is caught by the drive gear”, however I try to manually insert it into the small PTFE tube in the pulley body, then it is pretty seamless to preload the filament into the MMU. This is probably why the manual says the filament has to be straight in the last 40cm. It is not yet very clear to me how this can be done perfectly as there is 1.3m of PTFE tube before the pulley and the filament in the spool is also naturally curved.

Other than these issues, MMU3 works quite fine without any problems. I havent had any problem during simple multi color test prints. I have also printed normal single filament (and large) models and it works as good as before.

These are the first two prints I made. The first one only changes color at layer boundaries so it can also be printed without MMU3 but it is a quick test print.

Penguin Pete is an actual color print with more than one colors in a layer.

Footprint Increase and Space Requirement

MMU3 setup requires more space than I thought. Naturally there is a space need for 5 filament spools. However, there is also the long PTFE tubes (65cm) from the filament to the buffer, and these (thus the filament) should not be bent too much (as it is pulled by MMU3 pulleys and by Nextruder). Because the cartridge buffer has to be removed when changing the filaments, it should also be accessible. However, keeping the filaments (spools) and the printer on the same table requires a lot of space, so I put the filaments on a shelf under the printer. The buffer still stays next to the printer, so the overall footprint is still increased. Additionally, there is the MMU3 unit on top of the printer which makes it not possible to use the simple IKEA Lack enclosure I was using.

There are some layouts people made optimizing this as much as possible (also using different buffers) but it requires quite a bit effort.

Color Print Time and Waste

A color print (with multiple colors in a single layer) takes much more time than I thought. Because there is a need to wipe the existing color, change the color, wipe the current color etc. If the model is small, this can be particularly annoying as it takes much more time than a single color print and a lot of filament (comparing to a small model) is used for wiping and becomes waste. It is probably less annoying for large models or models with multiple instances of the same object.

Nozzle Cleaning and Probing

Before having the MMU3, after I print something, I was not unloading the filament from the nozzle. So the next time when I start printing, both the nozzle cleaning and probing was done with the filament loaded. The problem is, since the nozzle is warm (even if it is not totally hot all the time), some small amount of filament was melting and causing something to clean later. With MMU3, the filament is always unloaded from the nozzle after a print, and the nozzle cleaning and probing is done without the filament in the nozzle. Then, the nozzle is heated up to the right temperature and then the filament is loaded. I think this is cleaner and just works better.

Limitations

FLEX/soft filaments are not supported by MMU3, and I think this will not change in the future.

The multi-material options are officially limited to only PLA and PETG (including variants like NGEN and CPE) at the moment. I hope that the profiles for water soluble filaments (PVA, BVOH) will be available in the near future.

Summary

Particularly the time required for a color print and the limitation with filament types made me better understand the benefits of multi-tool printer like XL. However, I am happy overall with the MMU3 upgrade.