Now that it works, I should mention the changes to my heater, compared to the RepRap standard design. (See RepRap.org for the standard.)
Instead of the brass bolt for a barrel, I use a welding tip. It already has a 0.6mm hole at the tip, and it's easy to drill a 3mm or 1/8" hole at the top in a drill press. The smooth outer surface makes for good heat transfer from the nichrome wire.
I had several kinds of trouble threading it into the PTFE thermal barrier. First, I used a tap set to thread the PTFE, which created a good thread, but it expanded the hole above the brass, so that the melted plastic would expand too much, and be too wide to pull out, and too thick to push in. For my second try, I cut slots across the threads of a throwaway tip, and used that like a tap. It worked, but the threads were lower quality. The motor pushed the tip out of the PTFE threads.
My third try worked. I use a nut and fender washer to secure the tip. Then I hollowed out the PTFE in the shape of the nut, to keep it centered on the hole. Drill 3 small holes in the fender washer for 1/8" bolts that connect to the acrylic extruder frame.
The tip can be easily swapped for another, such as when I had to replace the tape with Kapton.