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Extruder design to prevent filament grinding

Posted by amatta 
Extruder design to prevent filament grinding
June 10, 2018 09:48PM
So I have noticed that some exturders have trouble when a lot of retractions occur in a short period. It tends to lead to lead to filament grinding that can lead to under extrusion and sometimes the filament getting completely stuck. What are some possible extrunder modifications to help prevent this? Do bondtech gears help? Is there a certain hobbed bolt/gear profile that is good at preventing this?
Re: Extruder design to prevent filament grinding
June 11, 2018 01:50AM
Yes, see [somei3deas.wordpress.com].


Delta printer calibration calculator, mini IR Z probe, and colour touch screen control panel: [escher3d.com]

Large delta printer, and other 3D printer blog postings: [miscsolutions.wordpress.com]

Disclosure: I have a financial interest in sales of the Panel Due, Mini IR height sensor, and Duet WiFi/Duet Ethernet.
VDX
Re: Extruder design to prevent filament grinding
June 11, 2018 02:54AM
... i found out by chance that laser marking a cylinder surface with parallel lines produces perfect (laser-hardened!) filament feed wheels with micro-serration winking smiley

This could be done with the motor shaft too, but have to test the "life-span" until the micro-teeth will be grinded down ...


Viktor
Re: Extruder design to prevent filament grinding
June 11, 2018 09:04AM
I saw someone using the flint wheel from a disposable cigarette lighter for a drive gear a couple years ago. I think the name of the extruder had "flint" in it.


Son of MegaMax 3D printer: [www.instructables.com]
Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]
Re: Extruder design to prevent filament grinding
June 11, 2018 09:06PM
The laser marking thing sounds awesome, how are you doing it? with a laser engraver?
VDX
Re: Extruder design to prevent filament grinding
June 12, 2018 03:23AM
... yes - here's a video, showing the prototype with turning axis, I've assembled two weeks ago for an exhibition last week:

[vimeo.com]


In the video it's marking text on a screw head, but this was the same with parallel lines for the "micro gear wheel" winking smiley

When at home again (and find the screws), I'll post some microscope images ...


Viktor
VDX
Re: Extruder design to prevent filament grinding
June 12, 2018 06:50AM
... I've engraved another screw with coarser distance, so better visible - with smaller distance the "grip" will be better:




Viktor
Re: Extruder design to prevent filament grinding
June 12, 2018 12:03PM
Did you trim down the edges of the bolt head as well? You should consider selling these if they work well. This is way too advanced to manufacture for the average maker.
Re: Extruder design to prevent filament grinding
June 12, 2018 12:34PM
thumbs up
I'll order a hollow one that fits over a 5mm shaft and can be adjusted axially, then fixed by grubscrew. That way you can use the whole length, if it is worn out.
Re: Extruder design to prevent filament grinding
June 12, 2018 01:30PM
The question of the density of teeth engraved on a hobbed gear interests me.

In my opinion, there must be an optimal spatial density, which is a function of the hardness of the filament material, and the force that tends to cause the teeth to penetrate this material. These two parameters define the depth of the indentations in the filament, and therefore the shear force that can be transmitted without the material crumbling. The diameter of the hobbed gear also plays a role, since it is related to the number of teeth that interact geometrically with the filament.

To put it more intuitively, very tight teeth will tend to slip on a hard filament, whereas if they are more spaced, they will have more chances to penetrate, to be able to transmit a significant force.

On soft material (nGen for example), tighter teeth will be more effective. And at the limit, on very flexible filament, a smooth surface could well be more effective than a toothed surface!

Edited 1 time(s). Last edit at 06/12/2018 01:38PM by M_Xeno.
VDX
Re: Extruder design to prevent filament grinding
June 12, 2018 04:32PM
... this screws/bolts were a "random find" in a box - the heads were slightly grinded down, to fit better into the slots of extruded aluminium.

The geometry and materials are free selectable - the sizes/diameters too (up to 90mm diameter with this turning axe and setup).

This was only a quick idea, so no actual plans to start a business with them ... but this can change, if the interest is big enough winking smiley


Viktor
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