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.

another Reprap addict...

Hi, I'm Alex, m, 28 , 'Informatik' student (computer science), from Germany
When telepath first told me about '3d printing@home' I wasn't sure 'bout it... it looked interesting but rather complex for a 'normal' person ( ... let's better not discuss normality). I read the articles about it and went on.
As he presented me the project a 2nd time, I was rather impressed, not only the project itself had matured, but there were also lots of interesting side-uses for some of the components (maybe later more about that, I have to prioritize). And since you have to start somewhere if you dont want an everlasting 'chicken-egg-problem' one of the possible side uses becomes a main use: A small PCB-milling machine driven by the Gen3 electronics as a RepStrap.
First we'll focus to use it as a RepStrap only and after we've build our own mendels maybe I'll convert it into a small pcb-mill.

Introduction from telepath

I've been fascinated by 3D printing ever since I read about Fab@Home some years ago. Just a few weeks ago some impulse made me look up the topic again, and I noticed that the project was as cool as I remembered, and by now you can even buy a fully assambled Fab@Home, but it's still much too expensive to make one myself.

(picture from fab@home wiki)

But I also found an article (german) which mentioned another project which they called "not so advanced", the reprap.

So I had a look around the wiki and was astonished, it's SO much simpler and cheaper than the Fab@Home. And since the article was from 2006, the "not so advanced" project was much more mature by now, with the mendel just being released.

(picture from reprap wiki)

Since then I was certain that I would follow the project, but as any hobby it's boring to do it alone, so I told my friends about it and one of them, Alex, was just as enthusiastic as me (well, maybe not quite as much), and so I got a good friend on board who has experience with atmel chips and stepper motors and who has been tinkering with a small mill for wood and circuit boards.

By now we have ordered all the parts for the electronics and mechanics for two mendels and are basically just missing the reprapped parts. Since it's a major problem finding someone who is willing to print the parts and has not already a bunch of people waiting, we have been thinking of a repstrap design, and I think we are on a good way. We have many diferrent opinions about which way to do something or how to solve a problem, but I think that will help us very much to find a good solution in the end.