Thinking about a dual extruder with 1 stepper & 1 nozzle

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Sebastian
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Thinking about a dual extruder with 1 stepper & 1 nozzle

Post by Sebastian » Fri May 20, 2016 1:05 pm

Hi together,
I'm thinking about how to do a multi-extrusion system from time to time. I don't want to have bowden system, I don't want to calibrate 2 nozzles and I don't want to add more weight than a single stepper motor. I had some ideas how to do that like two versions of an automatic filament changer (full retract and reload of another color) but all of them would need a "lot" of moving parts and extra stepper motors that need some µControler to control them..

Today I stumbled about the Dondolo extruder, a realy clever construction using a servo to clutch/unclutch two filaments on the two sides of a hobbed bolt and even sweep away the unused nozzle to prevent oozing. It still has two nozzles, but that should be avoidable with something like a dual version of the 4 way Flux Capacitor :lol: Awsome what can be found on Thingiverse..
So it would use a single hot end, retract the unused filament up to a point above the joining point of the 2 filament tubes, then use a servo with a pendulum to change the driven filament and start printing again after a prime.

Has somebody seen something before somewhere? I'm no friend of reinventing the wheel if there is already a working one ;) What are your thoughts about that? Maybe something like this would be worth some construction time..

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piercet
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Re: Thinking about a dual extruder with 1 stepper & 1 nozzle

Post by piercet » Fri May 20, 2016 1:11 pm

Thats an interesting approach. I've been toying with the idea of two coaxially mounted motors, with a hollow shaft on one of them with an inner shaft on the other. The first motor shaft would fit through the second one, allowing both motors to be mounted in approximatly the same spot, share a housing, and share gear locations. A clutch approach would work too. The upside to two motors would be simultaneous extrusion capability someday.

Sebastian
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Re: Thinking about a dual extruder with 1 stepper & 1 nozzle

Post by Sebastian » Mon May 23, 2016 11:56 am

I did some sketches to get a feeling what could work and what won't. I wasn't able to combine the Dondolo way of working with a gregs wade extruder, a direct drive is a must for this one.
But two filaments on one side of the hobbed bolt may work. The bolt has to be a bit longer than usual and there is another hobbed section, aprox. 9mm distance from the original one. The two idlers are moved by two kind of rocker arms, the arms are driven by a short camshaft with a standard servo.

Here is a rough sketch (not nearly finished):
Attachments
sketch.JPG

nbmoretto
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Re: Thinking about a dual extruder with 1 stepper & 1 nozzle

Post by nbmoretto » Mon May 23, 2016 1:22 pm

If you could use the E3D Cyclops hotend that would help with the single hot-end issue. I'm sure you could figure out a way to get direct drive out of that.

Sebastian
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Re: Thinking about a dual extruder with 1 stepper & 1 nozzle

Post by Sebastian » Mon May 23, 2016 2:22 pm

The problem isn't the two in one nozzle - the problem is feeding it with one stepper ;)
That's the thing i want to solve.

Sebastian
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Re: Thinking about a dual extruder with 1 stepper & 1 nozzle

Post by Sebastian » Tue May 24, 2016 12:59 pm

I'm not the first one thinking about a "cam extruder": Coherent Extruder: A 4 Color, 2 Motor Cold End
But all these extruders seems to be quite "beta"..

Today I recognised a mistake in my calculation regarding the servo: A gregs wade extruder needs about 6kg of spring pressure on the idler, not 0.6kg. :oops: I confirmed it with a kitchen scale. Maybe a very strong servo can turn this, but at last the cams needs some extra bearings to take bending forces away from the servo shaft. The other designs I found use a geared stepper to solve this - but a stepper is about 350g, a servo only about 50g!

Back to the drawing board.. But if it's working one day, the realy cool fact about such an extruder is that you can easily transform it from a 2 color single nozzle hotend to a 4 color, 2 nozzle hotend (our Rambo can't handle more heaters..) 8-)

Sebastian
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Re: Thinking about a dual extruder with 1 stepper & 1 nozzle

Post by Sebastian » Thu May 26, 2016 9:48 am

Calculated the servo forces, redesigned cam rod holder and cleanup. I'm feeling quite optimistic about that thing :)
Camstruder.JPG

Weekend_warrior1999
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Re: Thinking about a dual extruder with 1 stepper & 1 nozzle

Post by Weekend_warrior1999 » Fri May 27, 2016 1:56 am

Just an off the top of my head idea, but what about a dual channel wades extruder that feeds into a single hotend like you have above, and use a single push/pull solenoid to actuate the clutching mechanism that applies the required force on one filament or the other through which would be dictated by whether the solenoid is pulling or pushing. Im not sure what a solenoid would weigh to apply the required force, just thought id throw it out there.

Sebastian
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Re: Thinking about a dual extruder with 1 stepper & 1 nozzle

Post by Sebastian » Fri May 27, 2016 2:28 am

I read a little bit about solenoids in printers on Marlin GitHub. Even with small ones used for probe deploiment, you can't have them activated for a longer time because they get hot and use a lot of current. Keep in mind that we need 6kg (60N) of force on the idler, I guess that would require a very havy, big one with active cooling. Than you have no advantage against 2 independent steppers..

The servo and cam solution is very lightweight (servo is between 20-30 gram, compared to 350-400 gram of a stepper) and it should be even possible to deactivate the servo when it has reached it's end position.
There is only one possible drawback with this configuration: the force applied to the filament isn't variable as it is now with the thumb screw. Maybe this is a problem for soft filaments, i never tried them. If it is, there are two ways of solving this: put another (softer) spring on one idler and call it the path for flexible filament, or using a cam on one idler with less max. height so the spring isn't compressed to it's maximum.

I'm a little bit concerned about the necessary filament purge between each color change. This should be a problem of all 2-in-1 nozzles, but up to now I found nothing about it: To get a nice color change, it's necessary to purge all the old filament in the heater block. The hexagon has a very long one, so that's about 2cm of wasted filament on each change. If you have to switch the color once every layer, you might purge more mm of filament than it would be necessary for the hole print in one color..
An e3d v6 would be a better one for this, as it's lower with only about 14mm molten filament in it..

Sebastian
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Re: Thinking about a dual extruder with 1 stepper & 1 nozzle

Post by Sebastian » Thu Jun 02, 2016 9:02 am

Last post regarding this topic from my side for the next time.
The design is finished and I'm quite sure it will work at least after some final tuning. Also the BOM (bill of material) is completed. But I don't need two color printing in reality, that's why I can't overcome myself to spend the around 100€ to build one at the moment.

But if someone want's to do the adventure, I will give all the support and files to build one :)

Someday I will build it 8-)

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