As thermal insulator I used a piece of Celeron (aka Tufnol or hard linnen). I didn't expect to much of it but I just had to try because it was there. The specs say that it can resists temperatures upto 160 degrees celsius. Surprisingly it held out very well in my first test, the contact surfaces of the brass and stainless flanges became 200 degrees celsius.
The backside. It shows the stainless flange and the bolt that holds the inserts in place. The rod sticking out of the nozzle is a thermal couple connected to a display.
The frontside. You can see the coil from the soldering iron with the mica sheets between the coil and the brass.
The inserts. The nozzle has a 0,3 mm hole, the drill is next to it. Sweet isn't it? The hole trough the barrel inserts hasn't been drilled yet.
The connection of the heaterwire glows because of high resistance. Even without insullation, to keep the heat inside, the display of the thermal couple read 300 degrees celsius... As expected, the 50W from the soldering iron is a bit overkill. I'm planning to shorten the coil.
The testfacility. Unfortunately the ordered polymers didn't come in today so I haven't actualy been able to extrude yet...