After melting the PTFE insulator on my RepStrap extruder twice, I went back to the drawing board and replaced the whole hot-end assembly.
I manually turned the new nozzle and barrel on my mini-lathe. The nichrome heater wire will wrap right around the nozzle, applying the heat as close as possible to the tip.
The heater-barrel has a reduced outer diameter, my theory being that less metal there will reduce the flow of heat up into the PTFE insulator.
Here are a few pictures.
Extruder nozzle, with channel for nichrome.
Extruder nozle, flats are for a wrench.
Video of a first test printing
First 3D print from bill S on Vimeo.