Maybe the World's Lightest Extruder

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arsi

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1) The knife edge had to be symmetric, or the extrude and retract would be different.

I have tried different knife shapes and the best solution for me is to thin the bearing flange to 0.2-0.3mm and perpendicularly ground to the required diameter
The force required for rotation has not changed...

But the main problem, which appears with all knife shapes, I have not yet managed to eliminate. The pressure on the filament from the hotend, causes a change in the thread pitch at different speeds of extrusion and therefore the number of steps per millimeter. According to this video, I'm not alone [youtu.be]

I have been using my extruder for well over a year now, and this has not been an issue. Tom and I have discussed it, and I think that using high quality (ABEC 5) bearings and precision shoulder screws is pretty important. If the bearings can wobble at all, there will of course be an effect on the extrusion and retraction.

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arsi
But the main problem, which appears with all knife shapes, I have not yet managed to eliminate. The pressure on the filament from the hotend, causes a change in the thread pitch at different speeds of extrusion and therefore the number of steps per millimeter. According to this video, I'm not alone [youtu.be]

This is why RepRapFirmware supports nonlinear extrusion, to allow for the extruder steps/mm increasing with extrusion speed due to the increased back pressure from the hot end. See [reprap.org].

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

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dc42

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arsi
But the main problem, which appears with all knife shapes, I have not yet managed to eliminate. The pressure on the filament from the hotend, causes a change in the thread pitch at different speeds of extrusion and therefore the number of steps per millimeter. According to this video, I'm not alone [youtu.be]

This is why RepRapFirmware supports nonlinear extrusion, to allow for the extruder steps/mm increasing with extrusion speed due to the increased back pressure from the hot end. See [reprap.org].

Indeed, today I fired up an old geared hobbs extruder to check for this effect, and the same effect is there. I suspect that the results are so far down in the noise that no one has ever noticed it.
A slightly eccentric hob will far overpower any variation between hob tooth spacing.

Edited 1 time(s). Last edit at 09/18/2022 07:19PM by rq3.

Hi arsi,

Hum I've still a lot of job to get a fully usable extruder, but until now, with the tests I 've done, the cutting bearing makes a beautiful continuous thread mark, it is is very regular (visually seems to at least).

Which pressure do you mean instead, the pressure in between the wheels or the pressure to go through the heat block ? in my opinion, If it is to go through the heat block it means that your filament "glides" or "wears". Maybe the edge of the sharp bearing is not enough cutting, or your material is escaping like caoutchouc.

In my case the edge is sharp and it makes really like a clean microcut in the filament.

I'll work further and it, and report you the further results

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ADG AKA GA3D_tech ------ [www.instagram.com]------ [www.reprap.org] ------ [ga3d.tech]

Hi everybody,

Before that I go further in my project version of the kind of extruder I've done a quick pulling test, to check the capacity of my design :

Youtube - Pulling test Rolling Thread Extruder GA3D.tech

I want to cry, only a little load on the filament is already making a lot of problems.

the filament can be cutted, or twisted, it does not matter indeed, it is just not going forward.

Thank you @arsi to have me warned about that.

I must take a step back to find a solution or at least make a break on the topic until I find a smart lazy efficient solution.

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ADG AKA GA3D_tech ------ [www.instagram.com]------ [www.reprap.org] ------ [ga3d.tech]

But nonlinear extrusion would mean a new calibration for each filament and hotend temperature change.
First I want to try to include a bowden extruder in parallel. This could create a filament preload...

You're making a fundamental error in thinking. Been there, done that. The extruder doesn't PULL on the filament (except to get it off the spool). It PUSHES the filament in to the nozzle.

Edited 1 time(s). Last edit at 09/24/2022 12:32PM by rq3.

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rq3
You're making a fundamental error in thinking. Been there, done that. The extruder doesn't PULL on the filament (except to get it off the spool). It PUSHES the filament in to the nozzle.

It's easier to simulate it that way. But it's about the same thing. I figured it out by measurements on a real hotend during extrusion. (50mm of filament at 1mm/s vs 5mm/s and the difference was 8mm)
A conventional extruder will easily rip the filament from my fingers when I hold it or loses steps, in this case unwinding the filament from the spool will have an impact on the pitch of the cut thread.. And on Monday I will measure it on my hemera, I never thought to measure it and I'm curious about the result..

Edited 1 time(s). Last edit at 09/24/2022 01:30PM by arsi.

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arsi

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rq3
You're making a fundamental error in thinking. Been there, done that. The extruder doesn't PULL on the filament (except to get it off the spool). It PUSHES the filament in to the nozzle.

It's easier to simulate it that way. But it's about the same thing. I figured it out by measurements on a real hotend during extrusion. (50mm of filament at 1mm/s vs 5mm/s and the difference was 8mm)
A conventional extruder will easily rip the filament from my fingers when I hold it or loses steps, in this case unwinding the filament from the spool will have an impact on the pitch of the cut thread..

No. It's not "about the same thing" at all.

@rq3

Yes you are right traction does not exactly equal compression.

But in my case, If I push or I pull the filament, I have only one "knife" stuck in the filament, if the effort is enough to start the cutting process : I cut the filament instead of pushing it.

with my design I must add more blades to elevate the effort needed to start the cutting the process. I could do a kind of tube with many sharp bearing but I must think how to make it simple and easy.

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ADG AKA GA3D_tech ------ [www.instagram.com]------ [www.reprap.org] ------ [ga3d.tech]