Wades extruder without the hobbed bolt?

I was just wondering if it would be possible to add a rubber ring (something like this: [2.imimg.com], but the right sive of course) over the M8 bolt and have that sit tight against the 608 on the other side? Has anyone else looked into this??? As for availability, I have a few I pulled out an old printer, same concept there, the printer pulled paper through with the rubber rings and bearings.
What do you guys think??

i think the rubber would wear quickly, if it was able to but enough pressure on the filament.

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[mike-mack.blogspot.com]

If it was the right hardness it would definitely put enough pressure on the filiment. The question is, what's the right hardness?

Only way to see is pull one out of a printer and see.

I think there may be a problem in that residue from the filament will coat the rubber more than the rubber wearing out.
It's similar to the cause requiring replacement on the pickup roller.

I did some experiments trying to use a pure friction drive and I wasn't able to get enough drive force. I suspect that by the time you get enough compressive force with some sort of rubber drive roller, you will have either 1) mashed the rubber so severely that the drive torque is fantastically high (takes a lot of energy to compress the rubber), or 2) if the rubber is pretty hard, you will have mashed the filament out of round, which will also take a lot of drive torque because you end up deforming the entire length of filament.

The hobbed drive wheel works well because 1) you only are mashing small portions of the filament to form "teeth" along the filament, and 2) once the teeth are formed in the filament, you have a much higher effective coefficient of friction.

With a smooth drive roller, not many combinations of materials yield a coefficient of friction greater than 1.0. With teeth cut/mashed into the filament, the ratio of the drive force to the pinching force can be much greater than 1.0.

I've just tried using a friction drive with my Prusa Air, it works quite well actually, though I think it's Nylon, not rubber. As stated above, the greatest problem is filament residue.

cut a small notch in the rubber maybe to help grip the filament?

mesquka Wrote:
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> I've just tried using a friction drive with my
> Prusa Air, it works quite well actually, though I
> think it's Nylon, not rubber. As stated above, the
> greatest problem is filament residue.

That's cool - my efforts were dismal. Do you have any more details/photos?

Coating the nylon (confirmed, it's hard nylon), with paper glue improves grip (obviously), though I haven't tried it with the heating, just extruding, might cause some problems with glue mixing with the plastic. I've tried cutting a groove in the nylon, does improve the grip. I should probably wait until I fully complete my reprap (doesn't have a hot end, belts, or bed yet), and actually try printing with nylon grip.

After further testing, nylon grip seems to impractical, it seems to grip part of the time, but slips too much after the glue has dried. I think probably time to abandon this course.

Steve extruder(seemecnc) is friction driven. No rubber but steel. Double steel roller drive.

Thanks!!!

I think people should loose fear to make a hobbed bolt on the kitchen table. It's really simple:



You have the bearings already and all you need is some sort of a vice, a big washer, a hand drill and an M5 tap. Adjust the nuts to get the washer to the right of the wanted hobbed area, then simply hold down the rotating tap with the hand drill there. The washer makes sure the tap doesn't run away. The bolt will turn on its own. Oil prettyfies the result and reduces tap wear. Do that for some 30 seconds and you're done.

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Generation 7 Electronics	Teacup Firmware	RepRap DIY

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