Wednesday, March 25, 2009

 

Chocolate Extruder

Hello all!

Since it's my first post to the RepRap builders blog, I thought I'd better make it a good one. I've been blogging my RepRap build at Renoir's Rants and I've just started experimenting with extruders.

Although my RepRap isn't quite there yet ( the ABS extruder isn't quite working), I have experimented by building a chocolate extruder from copper pipe fittings and a drill:
From choc_extruder_v0.01
A copper tube and bowl hold melted chocolate which is fed to a drilled-out welding nozzle via an auger made from a drill. The heater is a standard nichrome wire and fire cement, along with a 100k thermistor, connected to the standard RepRap arduino electronics.
Drive for the auger is provided from a Tesco Value 3.6v rechargeable screwdriver. Currently, this is manually operated as I'm having a problem driving the motor using the PWM DC driver.

From choc_extruder_v0.01

The heater took a while to heat up, but the entire apparatus reached target at 60 degrees C. Shoving a few chunks of chocolate in, it melted very quickly.
Extrusion worked much better than I expected: when the motor was off, there was a very slow drip of chocolate through the 0.6mm welding tip (approx 1 drip every 5 seconds).
With the motor on, I was able to extrude a steady stream at several mm/sec and drew some lines on the plate. With the motor in reverse, chocolate was actually sucked back up the nozzle!
From choc_extruder_v0.01
All in all, I'm pretty pleased with the experiment so far. I've written up some construction details at chocolate extruder. A couple of photos are on my picasa album.

Still to do :

As soon as I've printed something, I'll post some pics. Might be a little while as I'm trying to get an ABS extruder working first...
:-)

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Comments:
Where to get a 3d model for a bunny? :)
 
I bet something a lot like a bigger, hotter version of this could be used to recycle plastic pieces. You could size the nozzle such that what it extrudes could be used directly as a feedstock for the standard extruders. Of course, with a nozzle that wide a valve of some sort might become necessary and unusual steps might have to be taken to cool the new plastic filament in a reasonable amount of time.

Thoughts?
 
Seeing as the reverse direction sucks chocolate back up the nozzle. You could possibly reduce, or even eliminate the 5 second dripping problem by running the motor in reverse for brief periods every second or so whenever the extruder is stationary for a extended period of time.
 
The DC motor board doesn't deliver enough current to drive the hand drill motor, all it will do is whine at you.

You can do it with the PWM driver board if you gang two channels together and put a EMF kickback diode across the output.

You will then have a single rotation direction and vast difference between the load and no load speeds.
 
Yep, I found I had trouble driving a large 3.6v screwdriver motor.

I replaced it with the standard BfB extruder motor/gearbox - which appears to have *plenty* of torque!

That motor already connects nicely to the electronics.
 
@BeagleFury: There's a (particularly famous) 3D model for a bunny here: http://www-graphics.stanford.edu/data/3Dscanrep/ :)
 
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