I’ve made a paste extruder(plunger type), in which a plunger will push the syringe to extrude. Plunger movement is controlled by a stepper motor. In that arrangement, for g-code generation I’ve used inside dia of syringe as the filament diameter and inside dia of needle as nozzle diameter and to calculate extruder steps per mm, I"ve used the lead of threaded rod which controls the movement of plunger.
But it had several issues like air bubbles and unable to print thick pastes.
Later I’ve seen this video on Youtube https://www.youtube.com/watch?v=PeYb3snGrU8 . In which he later changed to a Auger bit mechanism and I’ve seen WASP LDM https://www.personalfab.it/en/shop/clay-extruder-kit-2-0/ already made a successful one.
I’m trying to make one of these. But in this mechanism how to calculate the steps per mm for Extruder?
Is it same as the lead of Auger bit?? What about the filament diameter in slic3r settings?? in wasp LDM for 3d printers other than wasp recommended steps per mm is 400. But they’re not telling how they arrived at it or what’t micro stepping ratio they’ve used
Anyone have any idea??
Thanks
Augers are not positive displacement pumps like syringes and filament extruders are, so the steps/mm has to be calibrated by experiment.
@Ryan_Carlyle There’are too many unknown parameters. Is there any method to find at least the filament diameter to put in slic3r settings???
I’ve to follow trial error method for filament diameter too??
Any advice to where to start???
@Athul_S_Nair filament diameter is completely nonsensical for a pellet auger extruder. You’re going to have to try random stuff.
I know mine would be different, but can you give me your configurations, filament dia used when slicing and steps per mm
Well do you know how much material the auger can shift per turn? how many steps it takes your motor to make that one turn, and therefore how many mm it thinks that is. then calculate it with volume of a cylinder, as you now have the length of the cylinder and the volume, solve for diameter.
@Justin_Mitchell it’s not that simple. Screw extruders are viscosity pumps, so the flow rate depends on three things:
- screw speed (not total turns, SPEED)
- plastic melt viscosity profile along the length of the screw
- nozzle size / backpressure
It’s not like a filament-pushing extruder where motor revs * hob circumference * filament cross-section area = flow rate, and you don’t need to worry about plastic temp or nozzle size. The calibration for auger type extruders is highly situation-specific and only valid for a narrow range of conditions.
@Athul_S_Nair slic3r is just multiplying those together internally to get a flow-per-step. The flow-per-step value is different for every auger type extruder hardware, microstep setting, motor gearbox, temp, plastic type, and nozzle size. So we can’t give any suggestions. Just pick a “filament diameter” at random and try different E-steps values until you get the flow right for your printing conditions.
@Justin_Mitchell What comes out of the nozzle may be in cylinder shape, but what comes out of auger bit is not cylinder.
when configuring step per mm for extruder stepper motor (for direct drive extruder)
steps_per mm = no. of steps of stepper motor * micro stepping/distance moved in one revolution
no.of steps of stepper motor = 200 (for 1.8 degree)
micro stepping = 16
distance moved in one revolution = perimeter of filament drive gear
see here we are looking at how many mm FILAMENT will move for one revolution of stepper not the extruded plastic comes out of nozzle.
For auger extruder I’ve to know the mm of paste comes through the auger, not through nozzle. I don’t think that’s possible, may be I could measure it’s volume. Even if I find that I’ve to know the shape of material comes out of Auger to find other parameters.
If I put some random value for steps per mm in the firmware , and some way I could find out how many mm of material will come through; say for a command for extruding 10 mm material, then I could calibrate my steps _per_mm by,
new_steps_per_mm = old_steps_per_mm*10/material actually extruded
Only if I could find the length, not volume.
Like @Ryan_Carlyle I’ve to fix one value and find other by trial and error
The slicer software only wants to know the filament diameter and steps per mm so that it can calculate what volume of plastic is pushed through the nozzle for a give number of steps. It does not matter one bit what shape etc.
Now, if the auger has a defined volume per turn it outputs then great, we know how many steps there are for one complete turn, so we can calculate how many mm of an imaginary filament that would be.
If we dont know the defined volume, then set it up and extrude several mm at once then weigh it, PLA has a density of 1.25g per cm³
a 1.75mm filament would be (1.75/2)² * pi = 2.405 mm³ per mm extruded of standard filament.
so once you know the volume output of the auger, and how many steps it took to extrude that much, you divide by the volume of standard filament and you have your settings
@Justin_Mitchell for example;
My current steps per mm for extruder = 98
If I give the command to extrude 10 mm of a standard 1.75m filament,
then no. of steps required = 10 * 98 = 980 steps
If I use same motor and steps per mm to in AUger extruder and gave a similar command to extrude 10 mm material and weigh the extruded paste.
The weight of extruded paste = 5 g
The density of paste = 1.76 gm/cm^3
Then the volume of paste, V1 = 5 * 1.76 = 8.8 cm^3
volume of 10mm, 1.75 mm dia filament, V2 = pi * r^2 * h
==> V2 = pi * (1.75/2)^2 * 10
==> V2 = 24.05 mm ^3
==> V2 = 0.02405 cm^3
Then,
New steps per mm = Old steps per mm * V1/V2
= 98 * 8.8/0.02405
= 3585
Is this what you mean??
If not please give an example???
You have made a mistake early on, multiplying in a length that didnt need to be there.
If 5g was extruded by 980 steps then thats 2.84 cm^3 total volume.
Now in terms of 1.75mm filament that would be:
2840 (mm^3) / ((1.75/2)^2 * pi) =
2840 / 2.405 = 1180 mm equivalent of 1.75mm filament.
980 / 1180 = 0.8305 steps per mm
not such a useful number, so lets instead do it in terms of a fictional 10mm filament.
2840 / ((10/2)^2 * p) = 36.2 mm of10mm filament
980 steps / 36.2 mm = 27.1 steps per mm
Thats still rather a fast extruder, if you have a massive nozzle then fine, but otherwise you may need to look at increasing the number of steps, either using higher microstepping, or physical gearing.
@Justin_Mitchell “If 5g was extruded by 980 steps then thats 2.84 cm^3 total volume”
2.84 cm^3??
How did you get that??
If the density of paste is 1.76 g/cm^3, then
volume = 1.76 * 5 = 8.8 cm^3
Isn’t it???
The weight of extruded paste = 5 g
The density of paste = 1.76 gm/cm^3
So you extruded 5/1.76=2.84cm^3
Which you also said took 980 steps.
@Justin_Mitchell Okay,
I’ll try this
Thanks
