Granulate Extruder

The possibility to use plastic granulate instead of filament would be a great addition to the reprap project. Granulate is the usual form in which plastic is available anywhere, and it is much cheaper than filament.

Because of that several approaches have been discussed, for example in the wiki, blog and forum.

(picture from reprap wiki)

The solution presented in the wiki looks most promising to me (especialy because it is confirmed that is basically works).

I want to make some experiments on this, and the problems I see now are the following:

1. The auger

This design uses an auger to transport the granulate to the nozzle.

Plastic granulate is available in various sizes, but the original ware should have a size of 3-4mm, so I need an auger wich is able to transport this size. Assuming the core is one third of the diameter, that would be 12mm. To be on the safe side, I would say a diameter of 16-20 mm should be ok.

I had no luck finding an auger of that size available anywhere, so I fear this would have to be a custom job, which would not really fit into the philosophy of the reprap project.

For now I'm going to try my luck with the second best I could find to replace the auger: A drill, "Schlangenbohrer" in german, I think it's "auger bit" in english.

I got three versions, 12, 16 and 20mm. It seems the 16mm drill should be big enough, maybe even the 12mm one.

Of course the drill must be rotated counter-clockwise, but I don't expect any problem there. I don't have any knowledge of the dynamics of liquids and augers, but the tip of the drill doesn't looks like it will be ideal to generate the pressure needed to extrude the plastic. Well, we'll see.

2. The barrel

The auger sits in a barrel, which has the nozzle at the end. That end is heated to melt the granulate, so the upper end must be cooled to prevent the melting of granulate in the reservoir, I hope a passive element is sufficient there.

I would like to have a screw thread at the ends of the barrel, so I can fasten the nozzle easily to the barrel as well as the barrel to the reservoir.

Until now I have not been able to find a threaded tube of steel or aluminium which fits one of the drills, or even a tube that is thick enough to be threaded.

3. The reservoir

The current filament extruders have virtualy unlimited material, because the filament can be received from a spindel next to the reprap. A granulate reservoir would have only limited storage of granulate. Also it can't be very large because it would become too heavy and bulky.

So we might need a way to refill the reservoir continuously, or to stop the reprap when the reservoir is empty and continue when the operater refilled it.

For the first experiments I'll settle for small parts, which don't need any refill. It should not be impossible to solve this problem elegantly later.

This is how far I have thought until now. In any case it will take a while before I can even start to experiment, I still need to build my reprap before that.