soft grip filament drive for extruders?

I'm trying to tune my Wades geared nema 17 extruder. If it goes too fast it grinds the hell out of the filament and it goes downhill from there, but then I was thinking... I can push the filament with my hand through and it can go much faster, the big difference between my fingers and the M8 bolt with teeth in it? My fingers form around the filament, and the pressure helps grip it instead of helping grind it.

Has anyone tried using a soft material like silicone, rubber, etc. for gripping the filament and shoving it through the extruder?

If this has already been attempted I'd appreciate that starting point, optherwise I'll give it a shot and see how far I get.

thanks,
Anthong

2 cents, have you tightened your springs enough? i think my wades geared extruder forces the filament through more powerfully than i can with my hand.

Yes my Wade's has better grip than my fingers. It will extrude ABS through a 0.5mm nozzle at about 50mm/s. It will do PLA at 100mm/s.

Edited 1 time(s). Last edit at 09/20/2010 12:32PM by nophead.

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[www.hydraraptor.blogspot.com]

I've been ripping apart old printers for parts, and they have lots of rubber grippers to pull paper through the machine. many of them are on 5mm shafts. If you can get your hands on an old printer or two I'm sure you would find something to experiment with. I'd be interested in the results.

The first pinch wheel that Zach of Maker Bot when he was still at the reprap store had a bead of clear silicone caulk around the edge of the pinch wheel. It worked. Don't know why it was dropped but I'm guessing that the toothed gear held the filament better.

Wish you would follow this up though. If you can find a small hard rubber wheel that has a bearing or bushing I think it would work.

Arvin
[ouch]
http://www.mcmaster.com/#drive-wheels/=8xju51 but its $17.58
[/ouch]

Rubber pinch wheels have been tried but they don't have anywhere like the grip that the toothed pulley has.

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[www.hydraraptor.blogspot.com]

Thanks all, I'll definitely keep my current extruder for printing my Mendel and tweak it to work as good as it can.

I will definitely try some experiments with a coated surface or a rubber wheel, and post a new topic on the results.

Ideally, I would keep my extruder and just make a new M8 bolt, it's always nice to have experiments where you aren't changing out too many factors. As I've been thinking about it though, I imagine a larger diameter wheel than 8mm would produce a better result, especially with a pliable surface on it.

again thanks for the feedback, I know the wades extruder is good and I need to tweak my build of it, and will definitely display the results of my experiments, even if they fail.

Has anyone tried multiple toothed driven wheels? say from a number of gears or a long worm screw for the main transmission?

I did wonder if you could use both ends of a dual output stepper motor to drive the filament at two points to increase force?
You don't want one driving and one slipping, that would get messy.

I know BFB uses a threaded rod for the feed, but I can't imagine that's much better than one good pinch-wheel?

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[richrap.blogspot.com]

I am going to attempt to use a brass hobbed drive roller, with a urethane idler roller on an adjustable but not sprung axle. We shall see if its effective.

Yep, dual toothed wheels has been tried at least on a MakerBot:

[www.thingiverse.com] - pic

[www.thingiverse.com] - details

That's a mean bit of kit. Very nice design, just what I was looking for, thanks.

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[richrap.blogspot.com]

Last week I had the opportunity to see inside a Fortus 400 and this is what I noticed. I focused my attentions on the extruder area and this is what I noticed.

The 1.75mm filament was pushed with only two small metal gear teeth. They looked very familiar to wades design with the m6 tap idea. The drive motor was not bigger than this motor (http://www.robotcombat.com/products/0-GM13A.html) and really looked similar. I think makerbot was on the right path with a simple dc drive motor, but needs to add an encoder. The commercial machine have a great advantage over the hobby machines because a 1.75mm filament compared to the 3.00mm filament is nearly 4 times less area. Thus required a lot less force to push the filament into the heating zone. To make a better machine I think both 3mm and 1.75mm filament should be offered in the future.

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I think makerbot was on the right path with a simple dc drive motor, but needs to add an encoder.

Actually, RepRap used to use DC motors for extruders as well - in fact MakerBot stuff is a derivative of this early design. See Generation 2 Electronics, even the rotary encoder is already there.

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To make a better machine I think both 3mm and 1.75mm filament should be offered in the future.

Feel free to tweak the current design, but also make sure you have a supply for 1,75 mm filament ...

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