Six Color – Color Mixing Hot End for Reprap

This is my contribution to the RepRap project.  See below for update.

I’ve been thinking about ways to make a color mixing hot end since I read Myles Corbett’s research.

This is a Bowden type extruder hot end that uses mechanical mixing, and has a water block or heatsinks for cooling.

It has a very short melt zone and uses stainless tubes to lower heat conductivity.

Materials:

• 3/4″ Copper rod for the hot end body (thermal conductivity: 204).
• 304 Stainless tube for the Bowden tube inserts, mixer tube (thermal conductivity 8.4 – 16).
• 304 Stainless rod for the mixer shaft.
• 1/2″ aluminum plate for the water block.
• Nichrome wire for heating element (and thermistor – not shown).
• Motor for rotating the mixer (stepper motor etc).

Here is the overall design (using a water block – see below for less complicated version):

Paul’s 6 Color Hot End Assembly. This would have a smaller motor than shown.

The stainless tubes would be threaded into the hot end body.

Paul’s 6 Color Hot End – Top View

Paul’s 6 Color Hot End – Side View

Paul’s 6 Color Hot End – Top X-ray View

Paul’s 6 Color Hot End – Side X-ray View

Close up of Hot End:

Paul’s 6 Color Hot End Assembly Closeup

Paul’s 6 Color Hot End – Mixer Shaft

A variation: use a mixer shaft that does not have a hex end, instead it would be full diameter so as to block all inlets – except for one vertical cut that would allow a single color to pass.  The stepper motor would need an encoder to be able to determine it’s exact position.  Then just rotate the shaft to the appropriate color for near instantaneous color change (if used that way then the mixing chamber would be shortened).

Paul’s 6 Color Hot End – Color Switcher

Update:

Thanks to feedback on the RepRap forum I have changed the design to be smaller, lighter, and easier to build.

I’ve removed the water block and replaced it with heatsinks which can be easily made (with a lathe) from 1″ aluminum round stock.  They are just 0.6″ tall.

The filament tubes, mixer tube, and mixer shaft have been shortened.

A mounting plate can be screwed directly to the center heatsink, for mounting to the machine, and for mounting the mixer motor (DC or stepper).  A baffle would need to be mounted between the heatsinks and the hotend body to keep air from blowing directly on it.

Paul’s 6 Color – Color Mixing Hotend – Air cooled – Side view

Paul’s 6 Color – Color Mixing Hotend – Air cooled – Top view

Paul’s 6 Color – Color Mixing Hotend – Air cooled – Perspective