WIP: Dual extruder

[Kjetilei]

Hi guys!

I have been working on and off on a dual extruder for the past couple of months. It has been in cooperation with Guillaume. I have been responsible for the design of the prototype and Guillaume has been giving me feedback and moral support

Dual_extruder3.jpg

Dual_extruder2.jpg

My design goals where:
- use components already in Guillaume's inventory (M4 bolts/nuts etc.)
- make it as compact as possible to loose as little printable area as possible
- COG as close to the sliding bearing as possible with as few upgraded parts as possible
- easy to work with the hot ends (in/out and height adjustment)
- enough cooling on the cold ends

Reaching the goals where made hard by using M4 parts, using bearings to support the stepper shafts and using individually adjustable/flexible filament tensioners. In addition it was hard to get enough of the cold end parts accessible for the fan to be effective.

I had to remove the M8 bolts normally used to secure the hot end to the extruder base due to too little available space to use tools effectively. Instead I ended up with a "clamp" based design that share similarities with Guillaume's updated extruder design.

The distance between nozzle openings are 21mm (WOW!) the hot ends are nearly touching each other

I have also cheated a little bit to retain as much printable area as possible and the right hot end currently sits outside the hot bed when the x-axis is "homed". That way I only loose about 1.5cm if only using a single extruder. Note that my previous x-axis belt mount upgrade gave me more printable width on the x-axis so I have not lost any printable area compared to a default Felix printer.

I have not noticed any degradation of print quality caused by the added weight. I have printed several really nice looking parts with the extruder barely hanging together (due to not having long enough bolts and other small issues).

I still have to try a long dual print to ensure that the extruder base can stand up to long sessions with heat from two hot ends.

I'm on my second working prototype and have the third planned/soon finished. It works nicely but I have identified a few areas I want to improve; better clamping of cold ends, better ("invisible") routing of the wires, finalizing design of tensioning arms and create a good air duct to cover both extruders for cooling the printed part.

Dual_extruder1.jpg

Dual_extruder4.png

Dual_extruder6.png

Dual_extruder5.png

If everything works out as we plan, Guillaume will most likely make it available for sale in some way or another. But Guillaume still has to decide how and when (and if).

I hope you like the design

Please don't hesitate to give me feedback. No need to be nice as long as it is constructive

A little footnote on the joys of dual extruder printing: Oh boy was I unprepared for the immature nature of multiple extruders in the RepRap world... I have searched high and low to piece together needed information for getting the firmware/hardware up and running and actually printing a dual colored model still takes quite a lot of effort. I have to use Cura to slice the model before importing it into Repetier. I then have to use manual gcodes to heat up both extruders and load filament (it can be done with start gcode and stop gcode commands but I like to be in control since it is still quite experimental).

Luckily multiple extruder support is becoming more and more normal and the newest Slic3r has some multiple extruder updates that I have not yet had the time to test.

[HLA]

You were indeed tending towards dual extrusion And this is very exciting

This is a massive mod - wonderful to see it happening. Please keep us posted on the progress!

[Kjetilei]

LOL. I had to bite my tongue when the reference to dual extrusion came up in the filament roll holder thread!

Thanks for your kind feedback I'll keep you updated.

[dognotdog]

Pretty sweet! I'm tinkering with a bowden type dual extruder design, but it's good to know there's a direct drive one, should the bowden not work out.

Can you describe what you had to do to the electronics/firmware to get it all working?

[Kjetilei]

dognotdog: We considered a Bowden type version in the beginning together with a combination of direct drive for one extruder and Bowden cable for the other but these options in our opinion would be to combine the weaknesses of two worlds. You would not be able to gain much speed (if any) and only on the x-axis so really no point and it would introduce some retract problems etc.

Remember that the weight carried by the y-axis is most likely higher than on the x-axis with a dual extruder (I can't remember the weights of the different components at the moment). But this should not stop you from trying a Bowden type design if you have the time do it

I only had to make a few changes to the configuration.h and configuration_adv.h files (I think that are the correct file names). I can post the files. You will also have to replace the air duct fan with the second extruder on the RAMPS board.

Please share your design(s) when you are ready for it

[dognotdog]

Yea, I do wonder how well the bowden type extruder would really work. But, I also figured this is a stepping stone to add even more extruders, eventually.

Maybe one day PVA will be available in Europe, and we can print dissolvable supports

Also, according to my calculations, the moving Y axis parts weigh about 650g, and one stepper about 350g. So with two steppers, the X axis already weighs more, don't know how much more the hot-end adds. Any more, and I see stiffness becoming a real problem. I can see a lot of overshoot already at high speeds. Need some advanced software mojo that can deal with less than ideal stiffness, we'll see. Anyhow, it's all wishful thinking at this point

[Kjetilei]

Yes. I think you are right about the dual extruder weighting more than the z-axis. Initially I was thinking of using shorter/lighter Nema 17 steppers but ended up with the regular size.

The prints I have made using only one extruder (but all hardware mounted) with production profiles does not indicate any added problems due to the weight increase. But then again my printer is not optimally configured and may still mask problems that are caused exclusively by the heavier dual extruder.

As you mention Bowden type extruders make sense with multiple extruders (>2). Go for it and report back

I have included the two modified Marlin configuration files:

Marlin_dual_extruder.zip

Schematics:
http://reprap.org/wiki/File:Rampswire14.svg

[HLA]

@Kjetil:
Again, great job you are doing!
A couple of ideas to improve stiffness:
- X-axis motor is mounted so weight is not an issue - why not use a powerful Nema23 motor? The robust Al-extrusions should hold it and there is 2Amps of current that Polulus deliver;
- Thicker belts (e.g. 9mm);
- Use smaller Nema17s for extruder - why did you still end-up with regular sized ones?

@Dognotdog: Bowden extruder is a real innovation that was introduced in the community. However, it seems that there are split opinions about it. Less control over extrude/retract (-) on one side and less weight (+) on the other side. I have seen one Ultimaker printing and the results were not bad, but my Felix delivers better quality (hehe). I hope you can test this and report back with results.

[gfeliksdal]

Awesome design Kjetil ...Really exciting to see dual extrusion on the Felix.

I wonder how much more x-precision and less overshoot the bowden extruder design will gain compared to the current situation. To reduce overshoot you can reduce the acceleration in the firmware, but that will of course loose speed of printing. One possible downside of the bowden extruder is that you cannot print with rubberlike filament. At least that's what i've heard, but no own experience to back it up.

I guess the smaller nema 17s on the extruder should also improve dynamics, It's approx 80 grams less weight per motor. So, that will make it on par with the y-axis. Also the new linear guides, will increase the stiffness and precision.

For multiple extrusions I've been thinking that there might be a way to have multiple extrusions with one motor and one or more hot-end(s). There should be some switching mechanism(solenoid) to switch color. This will keep the weight down and still have the precision of direct extrusion.

[dognotdog]

@HLA: have you successfully gotten more power out of the pololus? I cannot turn them up much above 1/4, then they start overheating. What's the secret sauce? I think the stepper motors currently on the felix are also rated for over 2 amps. However, that doesn't help with the stiffness of the belt. I also appreciate the fact that all motors are the same, and you don't need to worry about having all kinds of different replacement parts.

@ gfeliksdal: New linear guides?