Combining several recent ideas from the forums, I've put together a quick and dirty extruder design. It uses many of the labour-saving tips (welding tips, the BfB 'big washer' design, Nophead's excellent resistor work) provided by others.
The PTFE runs right into a copper pipe end stop, which has an M5 drilled and tapped hole to allow a welding tip to be screwed in. The welding tip is *carefully* drilled out to provide minimal resistance to the extrusion.
Heat is provided by 2x 12Ohm resistors (wirewound, 6W, max 350degreesC) wired in parallel (which I reckon should give me a 6ohm load). Two resistors - one for either side of the nozzle - and they're squashed between the copper pipe end, nozzle, and a big washer on the bottom.
The big washer provides support to the PTFE barrel and is attached to the motor through long bolts.
I'm now soliciting any comments or advice before having a go at building this.
- ABS melt leaking along the side of the PTFE join?
- Not enough thermal inertia to keep the melt hot?
- Pack the gap around the resistors with FireCement to improve heat conductivity?
- Use silicone 'washers' to help seal the joint between PTFE and copper pipe?