Making a PID controller box for a 20lb melting pot

[WobblyHand]

Did you see the thread from a member here where he made some very nice swaging dies for pellets? Could be a good second op for uniforming those skirt walls.

I'm glad you're working outside and that the weather is nice. I've kept my mouth shut about working with lead. It's not the vapor/fume so much, since you're watching your pour temperature closely. It's all the contaminated equipment you're handling here. But you're an adult and can be safe.

What I really appreciated about this project is your power supply and PID controller. I've been thinking about rolling my own heat treat oven, because lab furnaces are too small and everyone thinks they are hard to build, which keeps prices up. Your control box would work perfectly for a HT oven as well, so long as everything was matched just like you did with your pot element. So thanks for the thread, I got something out of it.

I also think you should put a Miller decal on that blue controller box.

Yes, I remember the swaging die thread very well. As well as the lead wire extruder. The hard part for me would be creating the cherry. I don't have the grinding ability or tools to do that.

Pretty aware of working with lead. The crap really does get everywhere no matter how hard you try. I do clean nearly all of it up every time, but it is a concern. And yes, I do wash up after doing this stuff. I live in an old house in the northeast, so I'm aware of the dangers of lead and lead dust. Raised my kids in this house, knock on wood, no issues. (White paint = lead.)

Glad you got something out of the thread. Thank you for your suggestion of a circle cutter, that was very helpful. Made the job a lot easier.
Don't know that I believe it, but that kit SSR allegedly will switch 40A at over 300V, so it might be good for an oven. The fan isn't really needed indoors for the SSR, but out in the sun, that box heated up. I was glad I had put in a fan, the exhaust air ran relatively cool, even though it was 85F and in the bright June sun. The box itself was warm, almost hot from the sun.

Wish I could afford Miller Welders. I have a 185A Hobart MIG welder, kind of in the family, although maybe a black sheep... Used the blue paint originally to match my mill, so there was some left over. Safety blue definitely matches up with Miller colors.

 

[WobblyHand]

Think that the safety blue paint never quite cured. If you put anything on it, the paint eventually sticks to it. Kind of disappointing. May have to redo the paint or something. I put a piece of paper between it and the lid handle and the paint glued itself to the paper. So there's paper stuck to the paint in spots.

In the meantime, I didn't like the temperature range of the PID controller, so I bought a different one for the pot. This new one goes to 999C. This should give some head room. Before, I was near the very top range of the controller, which is generally not a good idea. I was surprised somewhat to find it was missing some contacts. Apparently this manufacturer left off the alarm relay contacts (and probably the relay) to save 12 cents. Fortunately, I'm not using the alarm function, as I don't plan to leave the pot unattended. At a total cost of about $12 or so, I guess that sort of cost cutting is to be expected. Still, if you think about it, it's a good deal of functionality for the cost.

Just switched over the controller box, but haven't done the all important smoke test. Located a spare thermocouple to give it a go in a little while. Now I have a spare controller. Thinking about doing a closed loop mold pre-heater. Have the hot plate already. When I used a hot plate it greatly increased the yield.

Basically there's not quite enough thermal mass in the lead of the pellet to sufficiently keep the mold warm enough. Now that the set point is no longer 5C from the absolute limit of the controller, I may get better regulation, and the hot plate can also keep the mold warm. Basically this problem is unique to pellets, as they tend to be low mass/volume compared to the molds. In my experience, larger bullets were far easier to cast and far higher yield. Hoping this pot/plate combo will help improve yield to a decent level.

 

[WobblyHand]

The switch over to the new -50C to +999C controller worked first time, which is a bit of a relief. Tested it out using our toaster over and let it run at the pre-programmed 100C set point. Regulated well enough, so passed it's 2nd maiden voyage. Not sure that I posted my schematics or not. I will have to go back and re-read this thread. It was my intent to post the schematics.

 

[WobblyHand]

I had a pencil sketch schematic. Really didn't want to bother with a "real schematic", so I tried to do it in LibreOffice. Jeepers what a pain in the neck! Lots of stuff that doesn't just work. (Or at least the way I expected!) Never tried to do something like this before with this tool. Finally got it done. Here's a pdf of the schematic. Nothing surprising, but might make it a little bit easier for someone following along. Hope it helps someone.