Must mixing ratios add up to a sum of 1?

tom_lauerman

Hello,
When looking at the Duet online configuration tool I noticed that when setting up a mixing extruder the configurator will not allow one to set a mix that does not add up to 1. Presumably this is to ensure that the total amount of extruded material is the same as it would be with a standard (non-mixing) extruder.

My question is, what if someone wanted to extrude "too much" or "too little" material, could one use a value of, for example, 1.5 or 0.5? Or is there something about entering a value other than 1 which will be problematic?

droftarts

@tom_lauerman See https://duet3d.dozuki.com/Wiki/Gcode?revisionid=HEAD#Section_M567_Set_tool_mix_ratios
Generally, you'll want to extrude with the mix values adding up to 1. The slicer only knows how much to extrude in total, and won't be aware of the mixing, so any value that is less or greater than one will cause under- or over-extrusion. The configuration tool has been set up to only allow the mix to total 1.

However, yes, if that's what you want, there's nothing stopping you from doing changing the mix, though you will have to do it directly in your config.g, changing the M567 values for each tool.

Ian

tom_lauerman

@droftarts Many thanks for your quick and informative reply Ian.

I use the mixing feature in a non-standard way in which one motor advances a syringe plunger to dispense clay while a second motor turns an auger screw to aid in flow adjustments. In order to synchronize the two I use the mixing feature, and the syringe and auger comprise one "tool".

So in my case I will often make adjustments that lead to a value greater or smaller than 1, I just wanted to be sure this wouldn't cause other unknown issues. I'll make this adjustment via the config file rather than the configuration tool. Many thanks again!

T3P3Tony

@tom_lauerman said in Must mixing ratios add up to a sum of 1?:

I'll make this adjustment via the config file rather than the configuration tool

Tom I presume you already know you can make this adjustment on the fly using by sending the command in the console, so you can tune the ratio while the print is ongoing?

tom_lauerman

@T3P3Tony Thanks Tony, I adjust on the fly with the sliders in the web interface, but I hadn't realized I could also redefine the mix ratio mid print via command. In that scenario is it effectively replacing the setting in config and becoming the "official" config setting?

deckingman

@tom_lauerman Not quite. The "on the fly" setting won't be retained when you cycle the power. So when you find a setting that works, you'll need to edit config.g to make the change permanent.

tom_lauerman

@deckingman Thanks for the clarification.

deckingman

@tom_lauerman said in Must mixing ratios add up to a sum of 1?:

@deckingman Thanks for the clarification.

No worries. For info, as others have said, the most usual case for mixing is with a mixing hot end where, if the sum of the ratios does not add up to unity it would lead to under or over extrusion. I know of one instance where a beta tester of one machine set a mixing ratio leading to massive over extrusion and the resultant pressure actually blew the hot end appart. I did suggest that this is a dangerous possibility and that there ought to be a some mechanism in the firmware to prevent this happening unless people really knew what they were doing but nothing ever came of it.