Monday, March 03, 2008


More Crazy Ideas

Like some others, I'd thought about a feed mechanism similar to Vik's but never pursued it. In search for a mechanism that would also allow backing out the filament (as a ratcheting mechanism like Vik's does not), I thought about how other cylindrical things move... namely snakes. Here's a hastily drawn diagram of a snake-inspired friction-based feed mechanism.

It seems pretty obvious that the closer you could come to bending the filament through full 180 degree arcs, the more force you could apply. There's almost certainly some great math out there for averaging force vectors and friction coefficients... Anyone?


First off, while pictures are worth a thousand words, I need some more words with your pic (and it's a pretty good drawing, mind) to get across what you are trying to do.

Second, unless your grooved wheel has a pretty huge diameter, I don't think that you're going to get filament to bend like that. This 3 mm filament is fairly stiff. It's not spaghetti by any means.
Right. Although someone _might_ be able to make a feed mechanism like this work, I doubt it's the best course of action. My intent in posting it was simply to sew another idea into this fertile field.

That said, my intent in dreaming this fictional feed mechanism up was to think of something that could feed filament in either direction, while nearly all of it's parts (at least the wheel, cowling, and funnel) could be produced by the reprap itself.

If someone wanted to pursue a feed mechanism like this one, making the inset groove a little wider and deeper, and lining it with some grippy substance like silicone rubber (perhaps siped? - ) might help. I don't know.

In no way was this post meant to be something I think will work well... just an idea someone might take and run with. :)
Ok a quick couple of things.

Timothy, I think your idea probably has enough mileage to warrant a thread on the discussion forum. Folk will probably find it easier to reply to you there and you will probably get more feedback as more folk seem to hangout on the forums.

On the cowling it probably would add too much friction if it were to work, and may be better replaced with a recirculating belt or a bunch of rollers.

On the grooved wheel, less serpentine tracks but a groove that takes say a couple of turns on the wheel will increase friction considerably. It does on most drum winches.

Thoughts for what they are worth...
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