Saturday, January 10, 2009


Feeding ABS with Worm Gears and Threaded Rod

Here's a method (inspired by all the other folk experimenting with alternative filament feeds) of feeding filament using Worm Gears and 3mm Studding.

Next job is to design the holder to mount it all to a RepRap extruder and a feed motor assembly.

The pitch of the M3 is 0.5mm per turn giving a feed rate of 0.5mm per turn of the drive shaft.

The tooth pattern cut into the gears is aprox 1mm deep so 0.33 of the diameter of a nominal 3mm plastic filament.

Whilst it all feels to grip pretty well I will need to actually make an assembly and do some measurements to see how well it works really.

I cut the worm gears myself on a mini lathe and they were surprisingly easy to do. The details can be found on my blog.

The technique should be adaptable for use with a Pillar Drill used as a lathe or Vic's Afghan Lathe.

I really like what you have been doing here aka47 with your worm gears. Do the come out sharp so they easy cut into the filament?

We might also want to look into the idea of using knurl wheels a drive mechanism. Knurling wheels are the tool us use to put grip texture onto a workpiece in a lathe. They are fairly affordable (about $10-15) for a cheap one. You can find them for sale all over the place, but Enco has some good ones. I was planning on either using the knurling wheel it's self, or a steel piece that has been knurled with a straight knurl.

However, these hand made worm gears you are making already have a guide feature and a gear reduction built in. Very cool.

If you used a knurling wheel you would have to have another wheel, perhaps with a vee or U grove, for the knurl to push the filament against.

What would be really cool is a set of knurled vee wire feed welding wheels, they cost about $30 for a pair. You should be able to get them at your local welding supply. They grip plastic filament like crazy, but they have a disadvantage. They have a large diameter ~ 1.625 inches. This requires a large gear reduction to get the torque and speed right to drive the filament.
Either way I'm highly in favor of this type of drive mechanism, it should lead to a more simple design with fewer parts. my 2 cents.
Very nice work. I really want to go this route (pinch wheels) as it just seems so much more reliable. I was considering having a way to adjust how much a wheel is pinching a filament to allow different sizes of filaments but haven't thought up a simple enough design. If I remember right the Stratasis machine I used in school used pinch wheels in a very similar looking setup i.e. 4 wheels in contact.
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