Thursday, 7 February 2013

After a long break working on other projects, I've returned to the Lego reprap. I gave up for a while because the extruder just didn't work properly. I kept getting jams in the nozzle I'd made - actually this is a known problem with the very early design reprap nozzle.

This time I bought a J-head IV nozzle from hotends.com .

I eventually came upon a good method of driving the filament using lego. I pinch the filament between two rollers. To work effectively the rollers have to be stiff enough to generate sufficient friction, but elastic enough to allow some slippage. They should rotate in opposite directions at the same (very slow) speed to pull the filament in.

I used two of the black lego driving shafts in adjacent holes as the rollers. They're driven by an old Lego technic motor. To achieve the extreme gearing in a small package with minimal friction losses, I've used worm gears to reduce the rotation speed. (I believe the lego motor has no internal reduction.)

The rollers have a section of grey Lego plastic tube slid over them to reduce the gap and because the tube is more flexible than the shafts. So it makes it tighter and gives some flexibility to the grip.

And.. finally, I have a working Lego extruder (albeit the nozzle is not lego, but lego was never going to survive the temperatures for extruding)!

video
I've included some pics and a video of the extruder working, hopefully the pics make it clear how this all works. Some of the pics show some plastic that's been extruded. The extruder is mounted on a temporary Lego frame for testing.
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