PID control of old RCBS ProMelt

[rogerpjr]

I have one of the old RCBS ProMelt furnaces ( 20+ years old) and want to control the temperature with a PID. Does anyone have a way to do this without mounting the temperature probe inside the pot? Has anyone attached the probe directly to the pot (maybe by the pour spout) or is there another way to set up the probe similar to the new model furnaces?

[HATCH]

You would disassemble the pot.
Weld a nut to the outside of the pot (under the shielding). Use a round TC and a bolt
Don't do the pour spot as its not gonna be a accurate reading of the lead.

[rogerpjr]

Unfortunately I don't have a welder or know anyone with one. But I may have to get one of the $100 HF ones. What would be the best location to locate the nut? Any recommendations on the model # for the thermocouple? I'll probably be using a MyPin controller.

[JimB..]

I’m curious why you don’t want a probe in the pot. I mounted mine by drilling a hole in an old aluminum hard drive platter and setting it on top of the pot. Couple magnets hold it in place.

[rogerpjr]

Cleaner install. Prevents junk/debris getting caught behind probe and makes stirring easier.

[Mr_Sheesh]

Use a MAPP gas torch and braze the nut onto the pot, should work well enough?

[cheese1566]

Aren’t the RCBS pots stainless steel?
I could be mistaken, but mine sure look like it and don’t get rusty.

[scotner]

I mounted mine on a small steel strip and added two magnets. Then PC'ed it to make sure the magnets stay with the bracket. You can position it anywhere you want it in the pot or remove it to add ingots or flux.

[rogerpjr]

I kind of like that magnet mounting idea. I did just locate a TC with a ring mount for only about $2.50 on Amazon which I may pick up just because of the price. But I'm not real thrilled about cutting all the rivets I just put in after I disassembled the whole unit to clean it. For some reason there was a lot of lead inside the housing amd I needed to redo the insulation around the pot too. Unit works fine now but I still can't figure how the lead got inside.

[lightman]

I used a piece of flat bar stock about 2 or 3 inches long with a hole drilled in each end. Its bolted under one of the existing bolts on top of the pot. I used a double nut so that it will swing out of the way for storing and fluxing.

[Petander]

How much does the PRO-Melt temperature swing with the original thermostat?

[dragon813gt]

How much does the PRO-Melt temperature swing with the original thermostat?

It’s going to swing more w/ lead level than anything else. As the level drops, thermostat isn’t moved, the temperature will go up because there’s less load. W/ a thermometer you can adjust as needed. This is what I did for a long time. The PID allows you to focus of every other aspect because you don’t have to worry about the temperature.

[rogerpjr]

I have the same answer as dragon813gt. I bought a lead thermometer from Brownell's at least 15 years ago and mostly keep it in the pot. I adjust as needed as I add back discards or ingots. The PIDwill solve the monitoring of the thermometer for the most part.

[Petander]

It’s going to swing more w/ lead level than anything else. As the level drops, thermostat isn’t moved, the temperature will go up because there’s less load. W/ a thermometer you can adjust as needed. This is what I did for a long time. The PID allows you to focus of every other aspect because you don’t have to worry about the temperature.

Thank you for the reply.

I usually cast the whole pot at once until almost empty and seldom adjust it during the session. 750 being a usual start, many of my molds start working better around halfway the pot.

Now I know why.

I use two or three molds and a hot plate.

[bigbore805]

I added a home-built PID controller to my pot about 6 months ago but the pot seemed to be running too cool with the probe stuck in the lead. The RCBS Pro-Melt uses a capillary probe temperature sensor running across the bottom of the pot at the pour spout. I decided to hook up a thermocouple to the same spot and see what happens.
I used a type K washer probe from Auber Instruments and wired it under the capillary tube with a short piece of steel wire. It won't go anywhere and it's covered by the bottom insulation pad. The probe has a 6' stainless steel braided lead so I cut off a short length and wired it to a panel-mount connector on the side of the pot. I put a new connector plug on the remaining wire so now I have about 5' of tc lead going to my PID.
The first test yesterday was excellent. The PID kept the pot at 725 for the whole session and the .45-70 bullets were very good, no wrinkles and no frosting.
The temperature will be difficult to control with less than about 3/4" in the pot because the heating element goes mostly around the side and there is only one line going across the bottom of the pot. It's probably there to act as an anticipator for the capillary tube.
I will be doing much more testing in the coming weeks to see if this is really a good solution but it seems to work well.

[Mike W1]

Believe the OP was concerned with having the probe in the pot and in the way. When I first did my pot that was of concern to me also. In reality it doesn't present any real problem. Just made the hole in my holder a little larger than the probe itself and it's still easy to skim around it as it'll wiggle some. Stayed with the seemingly recommended 1/2" off the bottom and the side. I just use the Lee 10# pots and cannot really ever detect any temperature difference from top to bottom other than when adding lead or sprues of course and it changes pretty fast then but also gets a consistent, if lower, from top to bottom which also occurs rapidly. My method is to use a feeder pot set a couple three degrees hotter than my pour pot and usually only get 1-2 degrees drop at most. Always have hot lead available when needed and find it easier to get consistent pours by not filling the pour pot real full nor letting it drop real far down either. Used to use homemade warming shelves on my ingots but much prefer now to heat them on the hotplate instead that initially prewarms the mold or molds. Probably use a few extra watts of power this way but I like flipping a few switches and when things are heated up everything is right where I want it. Have weighed enough 1st bullets out to know they'll be as good as the ones a dozen cycles later. Kind of like (somewhat) riding the bike 40 miles or taking the car. Lots easier. I'll grant the bike will still get you there but the comfort level is lacking.