3D printer extruder. idea

[Krinkleneck]

I wasn't sure whether to post this in here or on the open source hardware board.  Since I am building a 3-D printer from mostly from scratch... again... I have been thinking about extruders.  The main problem that I am partaking in challenging is the multi-color extruder.  The design I have in mind would have 4+ colors attached to one main motor, but activated by small servos.






 My thoughts on this would be to one high torque motor that drives to main gears with the filaments attached to swing arms that engage/disengage based on program.  The other option would be to use two motors in sync with same everything.  I already do this with my Z-axis for even lift, so synchronizing this shouldn't pose a problem.  Only software for the servos would add a few lines of code, and it looks like a copypasta job to accomplish all of this.  The only potential problem that I have been wrangling with is I need a default subsurface color, and I need white and black to be colors of their own to make CMYKW.  Unlike 2-d you don't have the advantage of your medium coming precolored white.  You also need a default color to take up a considerable amount of the volume so you're not wasting all of your color through the entire structure.  This issue of color and motor strength to power the colors are the simple problem. 
The main problems are shape and make of the extruder nozzle, and how the mixture will be done in the extruder so you only get the color that you want.  I believe the mixture can be controlled in software, but extensive testing will have to be accomplished.  With this being on my number 2 in my project list I am hoping for some ideas from veteran 3d printer enthusiasts.  Just to give you a heads up on what I am working on.. I am rebuilding my printer which is composed of wood, tube, and cold rolled steel.  I won't be able to touch any printing methods tell I finish rebuilding my printer.   My print bed only moves along the z-axis... and I am not using any standard measurements for anything.  My axis are powered by something by something inch threaded rod 14 turns per inch, and I mainly print PLA for anything.  So this project will have to be adjusted to my custom settings in firmware, and All abs printing is out of the equation as of right now.
Tell me what you think, and I would love some pointers on what you think I should do to move forward now that I have a cut from dirt rough idea.

[MacAttak]

I don't think it will work. You don't accommodate retractions at all. There are other things I think would cause problems - but that one is a show-stopper IMO.

[filip_cro]

You know that you need YMCK not RGB colors for printer?

I think that you will be best with white, black and YMC.

[Krinkleneck]

Sorry it took me so long to get back to you, but could you elaborate on the reatraction?  As for the motor that was the original concept with one motor, but the plan will probably move to two motors.  As for the retraction the only thing that would worry me is backlash.  If you move one main drive gear the other gear moves in direct opposite to make all filaments that connect to the drive gear move in the same direction, and when you retract they all retract.  So, I am a little at a loss on what you mean that it won't work.

[Krinkleneck]

You know that you need YMCK not RGB colors for printer?

I think that you will be best with white, black and YMC.

Yes, that's why I mentioned CMYK in the page, and I agree my big expense are going to be white and black first with the rest of the colors following.

[Maxlor]

If I understand right, you want to use CMYKW to get any color? That would be pretty awesome... but how would you properly mix the different PLA colors? If you join them before the nozzle and press them through, it'll probably look like striped toothpaste.

[MacAttak]

With your concept, how will you retract just one filament without interfering with driving the others? You don't want to just stop pushing one color through - you will want to pull it back slightly otherwise it will keep expanding and ooze forward. Most (all?) modern extruders will retract during non-printing moves otherwise you get nasty blobs and strings. For that scenario it is probably OK to just retract all filaments in unison - but there is still the problem of when you want to stop a specific color only.

[Krinkleneck]

The levers that force the filament into the drive gears have a retraction bar on them. It isn't clear in the illustration, but the natural state of the filaments is rectracted upwards away from the main drive gears. This means that you can have independent retraction with proper maneuvers. When the servos are activated, the line is then activated and being pushed into the main gear.  So, if you only want to work with specific colors at a time you just deactivate a filament. So if you want to deactivate/retract a color you just tell that color to turn off.  All I need is a good servo arrangement. 

Side note: I am debating on having its natural state as on.  I will have to cross that bridge when I get there though.

[Krinkleneck]

With your concept, how will you retract just one filament without interfering with driving the others? You don't want to just stop pushing one color through - you will want to pull it back slightly otherwise it will keep expanding and ooze forward. Most (all?) modern extruders will retract during non-printing moves otherwise you get nasty blobs and strings. For that scenario it is probably OK to just retract all filaments in unison - but there is still the problem of when you want to stop a specific color only.

That's the interesting part.  Someone has already figured out how to mix the colors together.

It's not perfect, but with this in mind I can get a leap forward on the proper mix settings.   So, that means before I can jump the bandwagon I have to....

• make the design
• get the code and settings that is being used
• refine to my hearts content
• poll my resources together, and hope for the best on this design

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[lapm]

I believe retraction is needed to prevent dripping effect, since plastics used in 3d printing expands when heated a slightly.

Some people just use print head that has multiply extraction heads and i believe i have seen one where several fillaments were inserted in same melting chamber to create mixed plastic layers.

[Krinkleneck]

Well retraction would still happen.  You would retract individually and by group.  So retraction would be taken care of.