I didn’t buy a thermometer for my furnace for the longest time. I just kind of figured I would know if the lead was at the right temp by seeing if the bullets looked right when they came out. Then I broke down and bought one to see if it really would help me out any. I can’t say that it did or didn’t. What it did show me was the wild temperature swings that I would get simply by adding a single piece of the sprue or dropping in another ingot to fill her back up again. Worse, the thermostat is just about pointless. It allows the lead to get way too cool only to heat it back up again way too much. So then I started reading up on adding a PID controller to a furnace. Some of the Castboolits guys go back and forth on what parts work best, where the parts should go, but one thing is for sure… Keeping the lead at a steady temperature seems to be VERY worthwhile. So adding a PID controller seems like a very worthy effort to go through despite the levels of effort and cost that will be involved. For anyone not sure what I’m talking about, here is a link that explains it almost too well:
Dual PID lead melting pot temperature controller and mold temperature