When the first extruder of my Rapman 3.1 broke I tried to fix it, as it was beyond the repair point I went to the manufacturer website to buy a new one but, at 200€ a pop, was too expensive for the durability it had so I decided to make a new one myself.
I found most of the information I needed at the manufacturers website and started the buildup.
The main component was a brass M6 bolt to which I made two holes, not at the first try I must say. First hole was a 3mm one through the threaded part of the bolt and was made with a dill press with the depth calculated to almost reach the head of the bolt. The second hole was an 0.4 mm hole from where the plastic was going to exit.
The chosen heating element was the nichrome kindly donated by an air heater, I used fire cement as an isolator and put a coat every column of turns, then waited for it to dry up. As a temperature sensor used a 100K NTC resistor, the website mentioned a 200K NTC resistor but it couldn’t find one, that meant that from that moment on, I had to compensate the temperature of the plastic that I selected for the prints as the resistor was going to give a different value than the expected by the electronics. NTC stands for negative temperature coefficient which means that as the temperature increases the resistance lowers.
For the first versión I bought a PEEK plastic bar that cost me a kidney (50€) and machined a 3mm hole through it and an M6 thread to hold the bolt. In later evolutions I found that PTFE (Teflon) is much cheaper and has a much lesser friction than the peek so I sticked with it. Both PEEK and PTFE are chosen for the very high temperature tolerance, ideal for this kind of application.
As the finishing touch I always isolate the extruder with Teflon or Kapton tape to reduce the heat loss and the heating time.
So if you find in the same situation as I did I hope you can learn from my experience, anyway nowadays the Hot End and extruders are much more easily available and are much cheaper.
Hope you enjoyed!!