I’m throwing my hat into the ring

Well, this is cool.

Inventables is throwing $40,000 at the first person to come up with a way to make RepRap filament at home. Luckily, I’m already working on this project (even though I’ve since started from scratch). Here’s what I’m up to, and what I’ve done so far:

The auger

Adrian Boyer and Forrest Higgs tried their hand at making an auger. Exhibit 1 and 2 Surprisingly, I can’t find any reference to anyone in the Reprap community trying to make an auger as they’re already made. Just take a look at this page. It shows an auger with a core that is larger at the tip than it is at the base, somewhat like this design of mine:

There’s probably a reason for no one investigating this type of auger. They’re really hard to make, and the contributors to the RepRap community (especially the innovators, less so the prosteletariat) generally don’t have really high-end tools like five axis mills.

Not only are these augers really hard to make, they’re also really expensive to buy. Here’s two I found on eBay:

Click to slightly embiggen

$500 and $1200 is far too much to include in a project that should cost $250. I’ve shown my ‘bar napkin sketch’ (below) of my extruder to many, many machinists, and they say this is a $1000 part. That’s out of the budget for this build, so I’ve got to figure out something. Hopefully I’ll have something by the end of next week.

The rest of the device

I’ve trashed my previous build. It wasn’t living up to expectations, and also looked really ugly. I’ve decided to keep pursuing Copper pipe as the main structural element of this extruder for a few reasons. One, everyone on the planet has access to copper pipe. It’s a standard of plumbing supply companies the world over. Two, it’s very, very workable. Instead of welding, we’re looking at brazing. Yes, that does have a few limitations (namely wanting to stay away from temperatures above 300° C), but it’s far easier for some garage tinkerer to put together a few copper pipe fittings than it is to weld stainless steel.
Here’s what I’ve settled on:
The plan is to have make a half-inch copper pipe into an extruder barrell. At the end, I’ll machine (on my drill press) a small brass plug that fits inside the pipe. This plug will have the necessary 1.75mm hole to squirt out the molten plastic. Like my previous build, this 1/2 inch pipe will be wrapped with Kapton, nichrome and a thermocouple.
Conceptual plug drawing
Around this Kapton-wrapped copper pipe, I’ll have an 1 inch diameter pipe to enclose the whole thing. I’m going to pour a bunch of JB Weld between the two copper pipes; the furnace cement I had been using isn’t quite up to the task.
That should pretty much take care of the extruder barrel. Once I have the barrel and auger, the only thing left is the motor controller/heater/tachometer/temp gauge Arduino shield Jesse from Hackaday is helping me out with. Should be easy enough.
I’m really hoping to get a lot of the auger and barrel done in July, just to get anywhere close to the competition deadline. Updates pending.
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