Simple Zero Ooze Dual Extruder - CRUX - no electronics, motors, or changed firmware

by galaxyman7, published

Simple Zero Ooze Dual Extruder - CRUX - no electronics, motors, or changed firmware by galaxyman7 Mar 19, 2017


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Update 10/23/17: The mechanism still works great almost 4 months later. The only thing that could be improved is the cooling fan mount, because it tend to slip down if the screws aren't tight. I made a little piece to keep it upright that I will include in the files.

Update 7/2/17: Updated the hotend holder cap (for normal sized hotends) to be more form-fitted in order to reduce cooling of the heat block. Changed the retaining arm for the extruder part to be less fragile and easier to assemble.

Update 6/18/17: I changed the design to work with either volcano hotends or normal sized hotends (just not both at once).

Update 6/17/17: The current version only works with the volcano hotends, I am working on a version for the regular sized hotends.

If you have ever tried a dual extrusion print, you know it can be a huge pain. The other nozzle bumps into what you are printing, it oozes all over your prints, and has to be primed before printing, which wastes plastic.
And if you try a mixing nozzle, it will constantly clog if you don't print with one of the colors for a while, one color will bleed into the next, and it can't use materials that aren't similar, for instance dissolvable support or flexible materials.

The CRUX dual extruder system eliminates all of these problems with a super cheap (less than $10!) and simple solution that requires no special knowledge to operate: No added motors, electronics, or firmware. Just build it and attach it, and change a few slicing settings. You can see the results in the images. The frog was printed at 0.3 layer height, so it does look rough but it was just for testing (I will upload more when I make more cool stuff).

Here's how it works:
The two hotends are at an angle to each other, and rotate together on two bearings. Rotating the hotends causes one to be vertical when printing, and the other to be "capped" with a metal strip, which prevents oozing. In order to rotate these hotends back and forth, the system uses a mechanism similar to a bike brake cable, but using a piece of filament and a bowden tube instead.
The carriage is switched remotely by the extruder. When the extruder gear rotates one direction (extruding), the mechanism pushes on the piece of filament, causing that hotend to rotate to the vertical position. While the extruder keeps extruding, the force remains constant, holding the hotend in place.
When the extruder rotates the other direction by 80mm (retracting), it will pull on the filament, switching to the other hotend. When the extruder un-retracts, it will switch back. The other extruder does not need any modifications.
The extruder mechanism allows for normal retractions (~ 6mm or less) without switching. This way you can just set your "extruder switch retraction distance" to 90mm in the slicer, and it will just work.

The youtube video below also kind of explains how it works (it is a bit old and describes problems that are now fixed):

Here is the parts list, not including the extruders and hotends (fits e3d hotend style and stock tarantula extruder):


Printed parts (see combined file for all on one build plate):
1x carriage
1x hotend holder pt 1 v2
1x hotend holder pt 2
1x hotend holder cap
2x peg
1x wire holder
1x extruder piece
1x pivot clamp
1x gear 1
1x gear 2
1x gear 2 cap
1x rack
1x magnet wheel
1x stage 2 v2
1x retaining arm
1x fan duct (optional for cooling fan)
1x fan duct linkage (optional for cooling fan)

2x steel sheet metal strips (these you will need to punch holes in, and bend to shape to fit your hotend)

Instructions for assembly:


Slicer setting changes:

Retract on extruder switch: 90mm
Retract on extruder switch speed: up to 100mm/s

Start G code:
G28 X0 Y0
G28 Z0
G1 Z5.0 F{travel_speed}
G1 X30 ;optional, positions the nozzle somewhere that works better for purging
G92 E0
G1 F600 E-90 ;pivots to first hotend
G92 E0
G1 F200 E20 ;purges first hotend
G92 E0
G1 F600 E-90 ;retracts first hotend
G1 F600 E0 ;pivots to second hotend
G1 F200 E20 ;purges second hotend
G92 E0
G1 F600 E-90 ;pivots back to first hotend
G1 F{travel_speed}
M117 Printing...

End Gcode:
G1 E-1 F300
G1 Z+0.5 E-5 X-20 Y-20 F{travel_speed}
G28 X0 Y0
G1 F1000 E0 ;brings filament back to nozzle to prepare for next print
G1 F1000 E0 ;brings filament back to nozzle to prepare for next print

M104 T0 S0
M104 T1 S0
M140 S0

Instructions for printing:
-The filament must be loaded all the way into each hotend before printing. You especially need to check this after stopping a print halfway through, since one of the filaments will be retracted by 90mm.
-If you are having trouble with the first layer not sticking, it's probably because your nozzles aren't level. Level the nozzles as best you can, and if it still doesn't work, try using a raft, which will make it much easier to get everything to stick.
-Don't be alarmed when you hear the extruder "clicking". The mechanism is making that noise, and it is normal. The two wheels with magnets are skipping past each other.
-You probably want to assign the extruder with the mechanism attached to the second extruder, so you don't constantly use it when you are doing single color prints. And you probably also want to use it for the part in the model that uses the least material, again so you don't constantly use the mechanism.

Print Settings


TEVO Tarantula


Doesn't Matter








2 perimeters. All supports are built in.
For me it takes around 8 hours and 100g of plastic for all the parts.

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Wow! Great work and documentation.
I would like to attempt to modify this to use a servo instead of the mechanical switcher, with your approval.

The equipment list shows a 30x30 fan but below is stated a 50mm, was that a change in design? The photo's look much bigger than 30x30.

Thanks again, really excited about the possibility of removing ooze from dual printing.

Yeah it's a 50 x 50 fan. Thanks! I have no problem with people modifying the design as long as it is posted under a remix. A servo might make it easier to build, but harder to set up correctly for slicing, firmware, electronics, etc. I try to shy away from that stuff if possible because of that. Just fyi.

I am getting close to finishing this, I have the scripts worked out and the Servo working to get this working. I had one question for you, do you want me to keep your "Krux" text on the body?

Sure, that's cool with me :). Make sure to send pictures when its done!

Great Thanks!
Yes the process is way out of my comfort zone. I am forcing my son to do the research for the firmware, already found options for the Slicer for switching so it should be possible, I know I'll end up doing it all myself ;-)
Don't hold your breath for a quick turn around, parts ordered from China already and I'll need the motivation to push it.

Again, great work!

Wow great design man.
What size blower fan will it fit?

Thanks! Here's the exact title of the blower fan I got on aliexpress:
High Quality DC 12V 0.06A 50x15mm Black Brushless Cooling Blower Fan 2 Wires 5015S

I can't seem to see where you describe what magnets to use... am I missing something, or where did you get the magnets?

They are listed in the linked google document that has all the hardware (in the description). They are 3mm diameter, 1.5mm thick magnets from Aliexpress.

I posted some pictures of a dual color benchy. However, keep in mind that I am using 0.6mm volcano hotends with cheap ebay filament haha. It tends to be more oozey, and doesn't do small features super well. I think printing a small prime tower may help, just to get the flow started consistently again before printing. I will try that out and also try printing with a support material.

This looks ace. Can you post some more pictures of what you've made with it? Thanks!

Ok I uploaded more pictures of the frog. It was printed at 0.3 layers, because it was just for testing purposes, so it is pretty rough looking. However, you can also see there is no oozing from the other nozzle getting stuck to the print. There are also no layer shifts or anything due to the mechanism.

Great stuff, thank you

I will definitely post some pictures when I print some more stuff. For now I will post more pictures of the frog haha.