This is my Multi Material Upgrade (MMU) for the Printrbot Metal Plus inspired by the Prusa MMU.
This collection of models has parts that I have remixed from:
Josef Prusa (I used his MMU for a base to make mine) https://www.prusaprinters.org/
SpannerHands (I used his MP spool holder to design the extruder mount) (https://www.thingiverse.com/SpannerHands/about)
Walter (I used his printable housing for printrbot extruder gears) (https://www.thingiverse.com/walter/about)
Please check them all out.
This modification does limit the Z axis to 220mm from the standard 254mm, this wasn't a problem for me as I never used the full limit.
This modification has been made to fit MY metal plus which is already modified with the SpannerHand's mods, this involved cutting the X cart which also moved the Z sensor and using a blower fan for part cooling. If you do this mod you can either also use his modifications and you'll be good to go. If you do not want to do the SpannerHand's mods, this will work with an uncut X cart and you should still be able to use the Z sensor as normal, HOWEVER the part cooling fan may not line up. This will be the same for an E3D v6 and UBIS hot end mount, when I make them.
Update - 08/04/2018:
I have now removed this mod from my Metal Plus, I was having issues with the printed extruders and I didn't want to but replacements. I'm now building a D-Bot ;-). Good luck if you do decide to build this, share your results if you do.
Update - 07/02/2018:
This is the wiki page I used for the wiring guide, http://reprap.org/wiki/Adding_more_extruders
Update - 28/01/2018:
I have made some mounts for both an E3D v6 and a UBIS 13S hot end, these haven't been tested other than a quick test fit but them seem good. I am not sure how well these hot ends will work with the MMU so use at your own risk. I have also remixed part of SpannerHands Printrbot metal plus mod, the lower parts of fan duct "should" fit without any modification and allow you to use either the E3D v6 or UBIS hot end with a blower fan and the lower ducts included here, the parts are named to show which is needed for which hot end.
This is made to fit my Printrbot Metal Plus with the single extruder, it mounts to the metal cart of the X axis with 3 M3 bolts which screw into M3 brass inserts, that have been inserted into the printed part with a soldering iron (See picture). It is as it stands for the DisTech Prometheus V2 Hot End, a E3D V6 & Printrbot UBIS mount coming soon.
I have remixed the Prusa filament guide to use M6 brass inserts (These need cutting shorter, see picture above) and M6 pneumatic fittings. My filament guide does not have tubes in as I drilled out the holes a little but this is up to you.
Included with the filament guide and Hot End camp STL parts you can use the optional dual colour logo's or use the NO_LOGO versions.
I am using the Printrbot gear head extruder gear set. These do not come with the small bearings needed so these had to be ordered from Aliexpress.
The extruders themselves are largely unmodified apart from making holes bigger for brass inserts, they were made as a mirrored pair and mount on the extruder mount with M3 bolts into M3 inserts. The mount uses Spannerhands idea of attaching to the metal frame of the plus, I have added cable tie holes to keep them in place.
Lastly as it is important that one filament is clear of the filament guide before another is inserted I decided to use clear PTFE tube, to help spot if something isn't going well and cut the power before bad things happen. I also think they look cool.
I'm using an Arduino Mega & RAMPS 1.4 board for my main controller, this of course only allows 2 extruders, so I am also using Printrbot's Extrudrboard for the extra 2 extruders. This is connected to the AUX-2 pins on the RAMPS and the firmware configured to use those pins.
So as I said above this set up uses brass inserts embedded into the plastic parts. I insert them with an old 30W soldering iron, just heat it up and place it on one side of the insert while holding it against the plastic part and it melts right in.
The hot end mount needs 5 M3 inserts, 3 are placed in the back of the mount to screw it to the Metal Plus X axis cart and 2 more inserts are need on the front for the hot end clamp to screw into.
The extruder(s) need 1 M3 and 1 M6 insert, these are for the PTFE connector and for screwing the extruders to their mount.
The filament guide needs 4 M6 inserts which if you use the ones linked about need cutting down (see picture)