Some people have had problems with their Solidoodles overheating, and having the hot ends fall apart despite using a temperature setting of 230C that is very high, but technically safe taken at face value. I know that the temperature reading in Pronterface isn’t necessarily an exact real world temp. You need to find out what temperatures tend to work for your kind of machine and stick with them, ignoring recommended temps from other, different printers.
Still, I wanted to find out what the difference is between temps reported in Pronterface, and real temperatures. I got a thermocouple, which is a temperature probe that attaches to a digital multimeter and taped it to the bare nozzle next to the thermistor. The ideal method would have been running it down inside the hot end, but unfortunately that is not possible for one built to take 1.75mm filament. I could have done it for a 3mm hot end.
Here is a “naked” hot end. The heat core is a special nut threaded on the outside and wrapped with nichrome wire, covered in ceramic adhesive. The nozzle screws on to the end of the threaded barrel, and the heat core gets tightened down against the nozzle so it can transfer the heat to it. The other end of the heater barrel goes into the insulator barrel which is lined in PEEK. The heater barrel screws into the PEEK, cutting its own threads. The PEEK keeps the heat from rising all the way up to the gear and prevents the filament from softening before it can be pushed down into the nozzle.
I set the temoerature at at various levels and checked the reading of the thermocouple against the reading from the thermistor reported in Pronterface. Then I moved the thermocouple up to the top of the barrel where it enters the insulator.
I gave each temperature change time to stabilize before checking the reading, and started from room temperature and worked my way up. I’ve only done this once so far, but a few run throughs would probably be necessary to get a good representation of the behavior. I think this is a good start however. I also want to run these tests while running plastic through the extruder.
It seems a little odd that the temperature change flattens out from 170-190. It did that with both the nozzle and barrel tests, but I’d like to run it a few more times to see if that is consistent behavior. One important thing to take away from this test is to never run hotter than 210. The insulator is rated to 250. After that point the PEEK will soften enough that the threads will give way and let the heater barrel fall out of the insulator. Setting the temp to 230 will push the barrel temperature to 260 or more, which is more than enough to melt the PEEK.
You can print just fine without going anywhere near hot enough to damage the insulator. However I think it would be a good idea to have some kind of cooling at the top of the heater barrel. There is a lot of extra airflow coming off of the fan on the motor. Maybe there would be a way to direct some of that across the top of the barrel, maybe with a duct that runs under or through the bottom of the X carriage.