I have exams these days and experiments on this are delayed by now. I'll try to make a video of it working as soon as I finish them
"Y" joint to feed a single nozzle with two different filaments.
With a bit of firmware tweaking it is possible to extrude multiple colours/materials with one nozzle.
Material switching is still experimental, and needs a lot of tweaking. Cold retraction is needed to properly clean the tip, and distances need to be calibrated or you may end up trying to put two filaments in the same tubing section. It can be also a bit time-consuming.
Anyway this has potential to be the grandfather of the multicolour printer of the future.
The presented setting has been tested successfully on a Prusa Mendel i2 with a customized firmware, an E3D nozzle and two jonaskuehling extruders, generating the gcode with Kisslicer.
The setting is pretty simple, all you need is:
-2 "Y" joint halfs, 3D printed.
-2xM5 bolts and nuts
-5xM3 bolts and nuts
You need to cut the PTFE tubing in a way that each tube has the shape of its place on the joint, AND all the inner surface of the joint is covered by PTFE. There is a photo with a red joint prototype up there that illustrates what you should get.
The next thing you need to do is bolt everything together, very tightly. The tubing must be prepared to withstand the extruding force.
The upper tubing goes to the extruders, and the lower one goes to the nozzle. Pretty straightforward, huh?
The software part
You are going to need some tweaking on your firmware to make your printer recognize that it has one nozzle with 2 stepper extruders.
I made that for you in this Marlin frankenstein I made from the last commit:
After that, you need to edit your extruder changing gcode routines to make your printer do what you want.
(Maybe, park extruder in a safe place, cool down, retract until out of the joint, heat up, extrude carefully to the tip, extrude a bit more, wipe, and go on with the print?)
This last part needs more experimentation. Not to mix the two plastics is still a challenge.