Model of the BFB's (http://www.bitsfrombytes.com) hot end (best hot end I tried). Unfortunately not easily manufactured if one does not have access to some fancy tools, but luckily BFB sell them as parts.
modules in the scad file:
hBarrel(diameter_of_the_nozzle);
This is the aluminum heat barrel. The heating wire goes around the "notch" (r=4.48). Thermistor goes into thermistor hole.
hPeek();
This is the PEEK insulator. Peek is used for strength and temperature stability.
hALU();
This is the Al tube that helps dissipate heat from the PTFE tube while strengthening the ptfe tube.
hPTFE();
PTFE (teflon) tube use for slipperiness and temperature stability. Filament is fed trough PTFE tube directly to the heat barrel. Peek and Al tubes strengthen the ptfe tube.
hREST()
This module contain the Al pressure "pad" that also works like a heat sink, screw holders, top MDF insulator and final acrylic insulator (can be also made of mdf) that pressures the PTFE tube to the Al. Make sure the PTFE tube is long enough so that final plate puts enough pressure so there are no leeks between ptfe tube and heat barrel.
You can see about the hot end itself:
bitsfrombytes.com/wiki/index.php?title=ManualUpdatesV30#head-assembly
