I ran out of ABS and I am switching to using PLA. I figured this was a good time to experiment with a stainless steel heater barrel. My first attempt was using a power resistor in a TO-220 package. This was easy to install, but I think it burned out because it sometimes doesn’t work. I didn’t have a suitable replacement, so I decided to build a heater using nichrome wire that only heated a short zone.
I started by cutting a piece of aluminum bar to get a piece that was 1 1/2 inch x 1/2 inch x 1/8 inch. I filed the edges and corners down so that they would not cut into the nichrome wire.
Next I drilled and tapped the center so that I could screw it onto my M6 heater barrel. I tried this in the past, but it was difficult to get a perpendicular thread on such a thin piece, so this time I drilled the hole into two pieces of wood as well, lined them up using the drill bit, clamped them together and then tapped through the first piece of wood and then through the aluminum. This held the tool perpendicular to the aluminum.
I screwed this piece onto the barrel. I then put the nozzel on tight and tighted the aluminum block to the nozzle to lock it in place and provide a direct path for heat from the aluminum block to the nozzle.
I attached the thermistor to the aluminum block. This creates good thermal coupling between the heater and the sensor. I’m using the old bang-bang control and having good coupling prevents overshoot during warmup and oscillations. With this setup, I have only 1 degree of overshoot. The downside is I don’t have an accurate reading of the barrel and nozzle temperature.
I also wrapped the aluminum block in a single layer of kapton tape to provide electrical insulation for the nichrome wire. I’ve found that this is required even for insulated wire because the insulation tends to break down due to the wire getting much hotter than the working temperature. Kapton tape stuck directly on aluminum or brass doesn’t get much hotter than the working temperature because it has a good heatsink on one side.
I wrapped the nichrome wire around the aluminum bar. I already had wire leads attached to the nichrome. I was careful to keep the amount of nichrome in the air leading to the copper wires short. This is because the wire can get very hot if it isn’t very close to another metal and tends to burn any insulation material that comes close. I had to redo one of the leads to get them both to be short.
To wrap the nichrome wire, I taped one end into position. Then I wrapped about half the nichrome wire around one side and taped it down to hold it in place. I ran a short bit along the edge of the aluminum block past the heater barrel (on the side opposite the thermistor) and taped it again there so that I could wrap the rest of the coil without the previous bit coming loose.
The connectors are steel butt connectors clamped tightly on each wire and then wrapped with kapton tape to prevent shorts.
After this I wrapped the coil in a few layers of kapton tape to hold it in place.
I also added a few pieces of tape that run along the wire connectors, down around the opposite side of the aluminum block and then back up to the other side of the wire connector. With another piece of kapton tape wrapped around the outside of the connector it is held in place without putting stress on the nichrome wire. I also wrapped some tape around the aluminum block on the thermistor side. This holds the thermistor in place as well as the pieces of tape that hold the connectors. Finally I put a few more pieces of tape on to make sure there weren’t any loose edges that might come loose.
The last step is an attempt to make the whole thing more durable. I’ve found that kapton tape that is in direct contact with nichrome wire tends to break down if it isn’t also in contact with a metal surface to cool one side. I’ve clamped a piece of aluminum sheet around the whole thing.
Unfortunately, I was not able to clamp it very tightly and so it isn’t helping much. I think if I did it again I would create three pieces of aluminum block that are the same size. The center one would be tapped as I’ve done here, but the other two would have larger holes in the center. The two extra pieces would be bolted together clamping tightly to the kapton tape.
Finally I mounted the whole thing on my extruder and tried it out.
At this point I discovered that with all the switching of barrels I have damaged my PTFE insulator . The only thing I can say about this insulator is that with an 8 Ohm heater and steel barrel it can reach 220 C without insulation and beyond 250 C with insulation.