Extruder calibration not consistent

[kasabian77]

Hey Guys,

i´ve replaced the minirambo on my Prusa MK2.5 with a Duet mini 3. My printer runs on 12v and the extuder motor is a Trianglelab geared Nema 17.

I calibrated the steps per mm with 1mms extrusion speed and noticed massive overextrusion on normal prints and hat to use a 83% extrusion factor to get decent looking results. Just now i extruded 110mm at 5mms and i measured about 20mm of filament left above the extruder.

Does it help to run the duet on 24v and control my 12v heatbed with a SSR?

Maybe someone can help me how to move onward from here.

MK2.5 Config.txt

[o_lampe]

@kasabian77
I think there is a mechanical reasons for this.
Loose grubscrews or too much friction in the gearbox?
Or the filament idler pressure wrong? To low and filament slips through the gears, to high and the motor can't push hard enough and skip steps.
In general the motor should be able to extrude at 5mm/s and 800mA. (with the right hotend-temperature)

[kasabian77]

I just checked the grubscrew and its fine and the filament tension was also good.
When i upped the temp from 205 to 220 i got to about 12 mm left.
It feels like the geared motor does not have enough power. On my original Minirambo board it was working fine, maybe the tmc2009 on 12v is to weak?

I think i will try to switch the duet to 24v and use my 12v bed with a SRR

[Phaedrux]

I recommend this method.

https://duet3d.dozuki.com/Guide/Ender+3+Pro+and+Duet+Maestro+Guide+Part+4:+Calibration/40#s165

[engikeneer]

@kasabian77 it might also be acceleration/jerk related? That would explain why you get less extrusion from lots of little moves (I.e. with lots of acceleration phases where steps may be lost). You could try reducing the extruder jerk/accel (might be that you've changed these from your old minirambo?)

[kasabian77]

@Phaedrux thats exactly how i did it 100mm at 1mm/s and i get 9,9mm left but at 5mm/s speed i get 19mm left.

[jay_s_uk]

@kasabian77 thats typical and suggests you need to calibrate non-linear extrusion

[Phaedrux]

Did you carry on and calculate your max extrusion rate?

[DanS79]

Keep in mind that this is a mechanical, fluid dynamic, and thermal dynamic problem.

If you increase extrusion rate, then one one or more of the following needs to change.

• increase the hot end temperature
• lower the part cooling fan speed
• increase the nozzle diameter

the extrusion/flow rate multiplier (slicers have various names for it) is nothing more than a fudge factor that allows you to make a tweak without changing one of the above.

Calculating your e steps at 1 mm/s will minimize the the fluid dynamic and thermal dynamic variables at play.

If you want to completely remove fluid dynamic and thermal dynamic variables, disconnect the extruder from the hotend. That way the only thing you're dealing with are mechanical variables.