Dual Extruders In The Space Of One Stepper Motor

The new hotness in 3D printers is – and has been for a while – dual extrusion. With two extruders and the requisite filament supply, it’s possible to print objects in two colors or two different materials. There’s a problem with this setup, though: each extruder requires a separate motor, greatly reducing the print area should you want to print in two or more colors. [Carl] and [Brian] think they have the solution to this with their dual extruder that is powered by one stepper motor.

As you can see from the pic above, the idea is relatively simple. Two strands of filament are fed past one gear attached to a stepper motor. Each strand is moved into the hot end through two idler gears and side of the extruder feeds into the hot end is determined by the rotation of the motor. It’s really one of those, “why didn’t I think of that” ideas.

[Carl] and [Brian] are also offering a quad extruder, a dual-sized extruder able to pump four different filaments onto a printer bed. With this, we expect some people to experiment with CMYK (or CMYW) prints, truly turning any 3D printer into a machine that prints full color parts.



76 thoughts on “Dual Extruders In The Space Of One Stepper Motor

    1. Ok, but if they called it the thunderdom extruder, e.g. two lines in, one line out
      would that make it more interesting (if not eventually, more expensive because of the
      licensing rights)

  1. The first innovators always draw the roadmap that others follow. Once these are out someone else will design a smaller, lighter version and before we know it full color 3D printers will be common. I just hope that these guys have well written patents to protect their concepts. If not then they will be over-run by others with deeper pockets.

    1. “before we know it full color 3D printers will be common”

      It doesn’t work that way though. Full color extrusion printing isn’t really possible. You can’t “address” each voxel to become a certain color. You can extrude bands of alternating colors but that’s about it. It’s AN advance (kinda) but the entire concept is somewhat flawed as it’s limited by resolution and unlikely to be able to improve. Still, it’s a neat hobbyist machine parlor trick.

          1. Conceivably, you can. You need to first establish, experimentally, what mix ratios generate what colors, and interpolate a curve.

            Additionally, you can control the feed rates of multiple filaments into the same nozzle to generate different colors. This has already been accomplished, and work is being done to refine it. (One extruder design even includes an auger screw to ensure the colors blend evenly.) You can find the writeup here: http://www.reprap.org/mediawiki/images/0/05/RepRapColourMixingReport-jmc.pdf

            From there, on the hardware side, it’s a matter of making a color-blending extruder compact, reliable, and capable of changing colors rapidly (so you’d either need an extremely short mixing stage or printer firmware that can look ahead and mix colors before they’re needed — likely both, come to think of it).

            On the software side, you’d need to extend G-code to handle multiple colors fed independently, you’d need a way to interpret color information across a slice as G-code.

            These are all difficult challenges, but there’s nothing to suggest they’re insurmountable.

        1. The issue is 3D printing In full color. Sure, you can pave over it by just coloring the filament, but that means using inks that will bond to your filament, and at that having it colored evenly and uniformly while it’s forming your model. Pretty tall orders

      1. I’ve been around long enough to remember when the first 7 pin dot matrix printers came out – they were the first dot matrix printers that would print true desenders (the part of the lower case “Y” that’s below the line). The printer was a technological marvel but the print head weighed over 5 pounds!

        And we have had color inkjet printers for a while now. Color inkjets don’t mix colors either, they print small dots of solid colors. It’s all about resolution & I believe 3D printers will get there.

  2. I’m not thinking that you could do CMYK as this system only allows one half to be extruding at a time, not both. I might be missing something but I would think that you would need to have all four feeding at different rates to achieve true full color parts.

  3. but what about retraction? my prints have issues with retraction turned off for jumps, and that’s even with only one head. sure, you get 2 extruders in the same space as one, but what do you loose in printing control?

    1. This design idea isn’t new. It was discussed at length a few years ago on the original makerbot operators google group. Consensus was the loss of retraction didn’t warrant the saved space/hardware. It’s just too important.

          1. So they are attempting to get a patent of something that was not only discussed in open forum before their application, but is also patented by another company? I wonder if they realize that…

          2. Not only that there is prior art. It’s called the automatic transmission.

            There is actually an electric transmission in which the gears are electrically engaged and disengaged with small clutches. Such a design would not only enable extruding multiple filaments, it is not patentable due to prior art.

            If I remember correctly, I read an article on it in popular science back in the 90’s. That would disqualify it for a patent.

  4. “Each strand is moved into the hot end through two idler gears and side of the extruder feeds into the hot end is determined by the rotation of the motor. It’s really one of those, “why didn’t I think of that” ideas.”
    How about because a 3D printer needs to be able to retract filament as well as feed it in? If you cant retract then you leave thin strings of filament every where when you move. It might work if you had some sort of solenoid selector, but not as it stands.

    1. Initially I was looking for a servo to control filament selection, because I just couldn’t see the point if you gave up the retraction. And servo came to mind before any solenoid because of weight/size/scalability for controlling filaments.

  5. Just my unqualified 2cents:
    I think for full color printing you would need 6 CMYKW because in normal printing the paper provides the white. As for mixing the colors together adding a small 3V motor with a shaft inside the hot end that spins around blending the colors could produce a properly mixed sample. This looks like an interesting step in the right direction but there are other ways to solve this problem. Having the extruder motors separate from the printing head running the filament through a stiff tube.

      1. The way I had envisioned it you would be blending the color streams as close to the nozzle as possible and the motor shaft would be creating a turbulence in the not plastic blending it. this would be a small volume of plastic so changing colors during infill could allow for clean color changes on the exterior of the product. the low volume of plastic would allow a “ok” pixel size with minor bending between colors.

        ow I meant 5 colors not 6 btw. the 6th would be support material.

        1. Since color applies to the surface and 3d printing is volumetric, the “waste” can be used to fill the inside of the part which we won’t see and as soon as the color is mixed properly we file the outer surface area.

    1. If someone manages to build a working granule to filament converter, perhaps one could create a varying color filament that has just the color sequence that is wanted. That way the mixer could be a larger device because it doesn’t have to move with the print head.

      1. This idea has potential. Maybe filament from the spool could be fed through a color applicator machine before it reaches the print head. Not moving around but still happening at the time of the print.

    2. Dont need a mixer like you mention. Look at the epoxy auto mix tubes, completely passive. IF you changed the colors mixed at the right times based on use you could get around the “waste” issue. It will not be perfect, but it will work.

      1. Static mixers, particularly helical ones, mix progressively but unevenly. Purging them is very difficult “on the fly” and there’s a considerable gap between starting the mix and finishing it, that varies based on pressure, temperature, plastic, etc. Plus, the pressures needed to static mix plastics are not trivial either.

        1. It’s “Patent Pending”, so I’m wondering if they rushed this out to gain some kind of an edge in the patent application process or simply to have a physical product before someone has a chance to copy the design – it seems like an easily copyable thing. Kinda reminiscent of the mechanical patents in the 19th century when people patented all variations of every mechanical part imaginable to keep competitors from producing them for 17 years.
          Anyhow, I can also understand that they were so excited about the product that they simply couldn’t wait – happens to me all the time :)

  6. This is far from a new concept. Stratasys has been using this setup for decades. The secret is to release the force applied to the idler on one side when the other is extruding or retracting. In willing to bet that if you looked you could find a patent for this that is old enough to have expired. While not new, it is still a sound design concept and it is about time someone has tried to apply it to open source 3d printers.

  7. Aside from retraction – how do they know how many steps did they loose when changing the filaments? Isn’t that important so that they don’t have holes or blobs in the perimeter of the object?
    Also who actually cares about colors – I think that printing with support material or flexible and stiff materials in one object is much more interesting and offers some interesting mechanical advantages!
    And if they care about the print size so much, why don’t they just stick one motor above the other one? Or make the machine wider?

    1. +1
      I have used a uPrint SE which has dual extruders that would lay ABS and a plastic that dissolved in lye solution. The ability to do that was priceless when it came to things like holes in vertical structures, or things that extended up and out. It almost bugs me when the first thing people see with dual extruder is two colors.

    2. “make the machine wider”. In the event there is a demand for a proven working version, the first market will be those who already own a printer. Extruder motors stacked vertically may not fit in an existing printer either As far as printers with a larger bed, the market for a printer that takes up more space on workbench or shop floor is probably limited.

  8. it’s clever but yeah issues with retraction and slop when switching colors.. could be tuned in w/ software and retraction just reduces strings a bit, not a huge issue. But maybe is is more of an issue with multiple head extruders? I haven’t used them.

    1. If you have a lot of retraction then you need to be better at designing and planning the routing. every time you stop extruding you introduce errors, so you should always have a continuous path. Make “waste” tracks that you snap off when finished if you need to, but a non stop extrusion system can be done if the print was designed right.

  9. With a disclaimer that I’ll never use a 3D printer, much less own one; In the event I win a lottery that makes me independently wealthy, I’d call the fellas up to say prove to me & those who use 3D printers a lot that this can work & $25K is enough to get started I’d fund it fully. After an agreement that production will take place(at least in part) in my small rural hometown which has a boat load of vacant building square footage. From what I seeing in the animations it shouldn’t be difficult, to construct a working model using hand tools(although it looks like they have access to at least 1 machine tool) along with easily available materials and parts to video record.

  10. Did I get this right, it gives up the ability to retract filament? They did mention something about retraction but it looked as if there’s only some preset amount of retraction, purely mechanical, that’s happening while the gear switches from CW to CCW – can anyone tell if that’s going to be enough for dual color printing?

  11. I’m disappointed to see Hackaday cover this – it’s a half baked idea from some not particularly eloquent guys trying to make a quick buck off of the 3D printing / kickstarter community – after apparently only experiencing 3D printing for 6 months. It already exists on other printers, isn’t particularly clever, and as others have pointed out, has major problems. Anytime the Hackaday editors want to post a story on 3D printing, they might put an ear to the ground – the 3D printing google group had this to say:

    Well, they say their models will have an auto-retract-feature – that might be some spring-loaded device that pulls the filament from the hotend when the motor disengages.
    However, the fact that they are going for a patent with their weird wobbly-face design should give you a clear hint not to support them. Plus, they got their first printer six months before the kickstarter, so these aren’t experienced operators either.
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    John Ecker11:17 AM

    Um this is already a thing in commercial printers. How can they patent it?

    Thomas Sanladerer11:19 AM

    +John Ecker which printers exactly?
    Plus, the patent might not even be for the actual mechanism itself, but for some sub-feature of the thing that has nothing to so with the actual driving process.

    John Ecker11:22 AM

    I’ve seen it in a dimension dual material sst.

    Stephen Baird11:34 AM

    And the patent is also pending, there’s every possibility it won’t be granted. But the fact that they’re going for one in the first place is enough to sour me on it. 

    Whosa whatsis11:47 AM

    The Uprint has a (patented, ugh) system that uses a single motor spinning in opposite direction to drive two filaments. Rather than using the motion of the motor to engage/disengage the filament, it moves the extruder to one side (where it presumably does a wipe) and presses the extruder block against a stop to flip a bistable spring mechanism to the other side.
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    Whosa whatsis11:48 AM+3

    As for these guys, I don’t think their mechanism will work very well, but screw them for trying to patent it anyway.

    Ben Malouf12:31 PM

    Beyond retraction issues, which I don’t see as solvable without using a dump system (like Stratasys), there is no cooling solution in their hotends. Yeah, I’d avoid this like the plague.
    Add a comment…
    View post

      1. Sounds like the essence of hacking…

        That was exactly what I was thinking, too! There’s absolutely nothing wrong with covering all manner of projects, including failed ones. Indeed, Hackaday has just recently solicited write-ups about failed projects. If it’s shown to fail, you now only have to find 9,999 more ways dual extrusion does not work before finding the one that does.

  12. they could add a cheap linear motor to the z axis and stack four of the dual filament heads in front of each other and get a octo extrude for the space of a dual extruder. and as it’s just moving a axle through the main motor it can be a small cheap motor switching the gear between each dual element in the extrusion array. the same tradeoff for speed versus versatility is being made, but at a cheaper price.

    I would say though my preferred way would be to circularly arrange the heads in a ring of bevel gears and have servo’s engage each head vertically into the ring as it’s needed. This would increase speed reduce cost as servos are cheap. you could then mix color filaments with multiple material types using the head but would be from a given set of dye filaments rather than being fully blendable. plus it’d retract but thats minor.

    any 3d printer going through kickstarter should aim to minimise cost in mass manufacture, I think in general this project is a step in the right direction. a machine on kickstarter that could make different filament gauges from pellets would be good though as that could bring down 3d printing costs.

  13. 1.It can’t retract the filament
    2.You’re going to have to add aditional parameters to account for the dead zone in the meshing of the gears as it transitions from one to the other.

    Point #1 is kind of a deal breaker though, that’s going to make some sloppy prints.

  14. Why doesn’t someone just make a head that has both an extruder and paint spray gun. Let the extrusion cool down enough then shoot it with some ink. Surface only but better resolution then blending with multiple strings of dripping plastic.

    1. You are thinking that the material retains it’s shape while laying down a bead of filament, but that is not true.

      1.75mm or 3.0mm filament is melted in the extruder and comes out as a much smaller diameter, say .3mm or .5mm.

      So painting the outside, then melting it to liquid is not going to work.

      On another note with this device:
      I am also worried some that the amount of retraction (to prevent dripping, etc) is a constant and not adjustable.
      When you extrude different materials you sometimes have to fine tune the extraction to a different amount, and with this design you cannot do so.

      There is also, with this design, a different problem. What if the gears do not mesh when you are moving from side to side–they could lose position as the main gear rotates to engage the other side and not put out the amount of filament you thought you were going to.

      If the reason for going for this design of dual extruder is not reducing the printable area, an option is to use bowden tubes and mount the motors on the frame. not much space lost for the second nozzle, 4 could fit in an 1″ square. Bowden tubes have their own design problems too, but I think some development of stiffer tubes and correctly sized tubes would reduce them greatly. Currently people use standard push-lock fittings and air hose with diameters designed for other applications.

      On the same area of a dual extruder with two motors, you can have 6 or even 8 hot ends with bowden tubes attached. Sure, machines need to be built with that in mind, but that is not hard to do, many are extending their printers now for more area.

  15. As has been said above, Stratasys/uPrint already does this (dual extrusion with a single motor) and has been doing so for years now. In fact, the prototype for this project looks suspiciously like the Stratasys one. Good luck getting a patent on that.

  16. The only way I can see of getting decent resolution for multi colour 3d is to print in white and ink jet each layer. I’ve got some ideas and one of those arduino drivable ink jet cartridges but it’s about two or three projects down on my to do list… I’d be interested if anyone else has any progress in this area.

    You would still need a dual extruder for support though….

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