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UM2s: UM2 Dual Extrusion Switching hack

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I got this switching mechanism idea already a year ago, but never took time to realize. Since I'm printing now a couple of months w/o any switching issue's, it's time to share this upgrade here on the forum.

It's working with a simple cam-plate, which is moving both nozzles at the same time. The cam-plate is bi-stable, by using the existing (UM2) springs which also hold the teflon isolator in place.


Benefits of this modification, besides enabling 2 material prints:

  • Simple modification on the existing hardware
  • Switching is done above bed clips, so no loss of additional print space
  • Modification works both on UM2 and UM2+


Switching in action:



Some prints:


Edited by EdgE
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On 3-1-2018 at 11:50 AM, jtronics said:

Hello, that's a nice solution (like UMO3). Has anyone else tried that?
Is it possible to generate the needed G-Code with Cura 3.X? Are there any scripts or something else?

Thanks, well a colleague has also one printer converted to this solution. He also created the Cura 3.x definition files. :)

His switching solution is activated by hitting the slider blocks. That will be a little bit quicker, but you loose also some mm printing space in x-direction.

I know also, that some other people are busy with this mod, but have not seen any pictures yet..


So there is a Cura 3.x machine definition available. (I will update this on my webpage.)

The Cura modifiction is working very simple. Within the extruder definition files (ultimaker2s_1st.def.json), I just changed the line:

"machine_extruder_start_code": { "default_value": "G0 F9000 X219 Y17.5\nG0 F1000 X223\nG0 F9000 X219" }
So here are the coordinates stored to do the switching action for lowering the left nozzle. A similar code is added for the right nozzle.

So the good news is, you only have the update the marlin firmware once and then you could just tune the switching coordinates in the json files.



21 hours ago, conny_g said:

I'd be a bit worried that cutting the bottom and removing the screws from the bottom plate makes the head much less stiff than before. Does that have any effects on the print quality?

Good point, I did add additional mass (extra heater block etc) and the bottom plate is indeed not bolted anymore. On the other hand, there is a big spring, which presses all play out of the switching construction in one direction. Also the screws are still connected to the upper plate, compressing the plastic parts a little. From my point of view, there is not noticeable more ringing, compared to the unmodified version.  If you know a very good test stl, send a link and I love to do some tests on this issue.

(I'm also modifying another printer, for (5x) higher printing speeds and here I do have issue's with stiffness resulting in ringing... But that will be a different topic.)


This picture shows hardly any ringing, but you do see some minimal layer shifting mainly in Y direction once in a while. I guess this will be around 0.1mm.


Edited by EdgE

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Generating gcode for this solution is pretty simple, like you do this with an UM3.


After a  nozzle switch (T0/T1), cura is executing the additional gcode automatically.

This could be found in ultimaker2s_1st.def.json:

"machine_extruder_start_code": { "default_value": "G0 F9000 X219 Y17.5\nG0 F1000 X223\nG0 F9000 X219" }.

Here you could place the commands for doing the switching movements.

See working example here: http://www.khwelling.nl/3d/pic/um2s_cura_definitions.zip

(These definitions are partly copied from UM3 & UM2. Be aware to save the right files in the right folders.)


So the only thing you have to figure out, where your exact switching positions are and write them in both extruder files.

(So this should also be possible on an UMO+.)


Strange Cura behavior:

Somehow cura 3.0.1 was still showing these 'machine_extruder_start_code', when showing machine travels after slicing.

With cura 3.0.3 these movements are not visible anymore, but still executed.

You see also some UM3 switching gcode paths, while you don't need them, since you are not using a UM3.

Edited by EdgE

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