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Thread: Mounting a thermocouple on Lee 4-20 Pot

  1. #1
    Boolit Buddy Tmaloy's Avatar
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    Mounting a thermocouple on Lee 4-20 Pot

    I would like to ask if anyone has an internally mounted thermocouple similar to the one in the pic below. I'd like to mount this in the center of the bottom of the pot using flat washers on both sides and locking them down with nuts to clamp and seal the drilled hole. Hoping the 4-20 pot arrives this week so I'd like to get some experience from others. I also have a Lee Magnum Melter and would like to do the same to it.

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  2. #2
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    JonB_in_Glencoe's Avatar
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    see post #71
    http://castboolits.gunloads.com/show...=1#post1280118

    bpratl mounted one in the center, but it interfered with a certain mold, so he moved toward one side.
    ~~~~~~~~~~~~~~
    “If someone has a gun and is trying to kill you, it would be reasonable to shoot back with your own gun.”
    ― The Dalai Lama, Seattle Times, May 2001

  3. #3
    Boolit Buddy Tmaloy's Avatar
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    Thanks JonB, I was hoping it would not interfere with the bottom of the pot. I am going to try something different then. I want to be able to switch between two pots for my PID controller. I have a broken battery operated grill lamp with a 24" gooseneck. I am thinking I can mount a TC to it and be able to place it in and out of the different pots and use the same PID.


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  4. #4
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    I like Tmaloy's (Post #3) idea. I have three pots I regularly use, and one PID. Notwithstanding this, all three generally get quite -- for lack of a better word -- "cruddy" -- and I bent a putty knife by squeezing it in a vice to match contour's of pots -- for cleaning. To *MY* way of looking at it, a thermocouple suspended from any sort of hanger -- my first was fabricated from a length of a wire coat hanger -- is the way to go. Further, the thermocouples I use seem to have a finite life -- one of mine di din fact die, so -- Murphy Law -- I ordered/received two of them so I'd have a spare. The spare is still in its bag, so perhaps original was defective? Don't know -- but, replacement effort, IF needed, is another consideration.
    BEST!
    geo

  5. #5
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    JonB_in_Glencoe's Avatar
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    Quote Originally Posted by Tmaloy View Post
    Thanks JonB, I was hoping it would not interfere with the bottom of the pot. I am going to try something different then. I want to be able to switch between two pots for my PID controller. I have a broken battery operated grill lamp with a 24" gooseneck. I am thinking I can mount a TC to it and be able to place it in and out of the different pots and use the same PID.
    Click image for larger version. 

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    If you want the TC to sense near the bottom, which is ideal, I don't think the braided lead wires on your short TC will handle the molten alloy. Also, if you read near the top, as the alloy level drops, that will be problematic as well.

    I use a 4" TC (100mm) and I mount it temporarily to the side of the pot, with a Clip that came off a the probe of a analog thermometer

    see post #572
    http://castboolits.gunloads.com/show...=1#post3059905
    ~~~~~~~~~~~~~~
    “If someone has a gun and is trying to kill you, it would be reasonable to shoot back with your own gun.”
    ― The Dalai Lama, Seattle Times, May 2001

  6. #6
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    HATCH's Avatar
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    You could take apart the pot.
    Weld a nut that has the same thread as your TC in the bottom center.

    On the TC you have shown, only the very tip is designed to be in contact with the hot lead.
    The stainless sheath is just for protection for the wires and provide mechanical support.
    If you submerge the braiding in hot lead it will eventually leak thru the braiding and short out the TC.
    Don't like being hammered by the Cast Boolits Staff, then don't be a nail.
    The rules are simple to follow.

  7. #7
    Boolit Buddy Tmaloy's Avatar
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    Thanks for input. The short TC I have in the original post is what I planned to mount in the bottom of the pot. I think I will go with the gooseneck and use a regular style TC. In case it needs replacement or being used between different equipment anyhow, it shoud be easier than disassembling the pot to get to it.

  8. #8
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    HATCH's Avatar
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    To be honest the temp of the lead will be the same near the edge as it is in the center.
    Molten lead in a small pot like the 4-20 will be within a couple of degrees across the entire pot.
    Don't like being hammered by the Cast Boolits Staff, then don't be a nail.
    The rules are simple to follow.

  9. #9
    Boolit Buddy Tmaloy's Avatar
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    Thanks all, just to clarify, my original intent was to place the short T/C in the inner pot through a drill hole internally, and use an appropriate nut/washer to seal the drilled hole. The T/C would be in the melt. The Lee pot should be here by Monday, so I have yet to get an idea of how much clearance the T/C would need being mounted in the bottom. If one way doesn't work, at least I can have the option to use the gooseneck.

    HATCH, looking forward to using your PID with my project melters. When you mean welding the nut to the pot, is there a specific type of weld to use or would silver soldering be enough to hold and seal the T/C in place with out leaking out. Thanks all for your input and time.

  10. #10
    Boolit Master Drew P's Avatar
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    You have to use an acorn nut inside the pot to retain the tc. Just drill a hole, and nut it in. It won’t leak. When you see the tc you’ll realize it won’t seal at all even to itself.
    No welding or sealing needed.

  11. #11
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    HATCH's Avatar
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    Quote Originally Posted by Tmaloy View Post
    HATCH, looking forward to using your PID with my project melters. When you mean welding the nut to the pot, is there a specific type of weld to use or would silver soldering be enough to hold and seal the T/C in place with out leaking out. Thanks all for your input and time.
    You have to remember that the pot itself can potentially reach 1k degrees F (if plugged in empty).
    You don’t need to puncture the pot.

    The Magma Master Caster factory TC is attached to the outside of the pot.
    The pot will be the temp of the lead or within a few degrees.
    It’s not rocket science so you don’t need the precise temp of the lead.
    You need a repeatable temp.
    For example on the star sizer with the factory heating base.
    I attach the TC to the mounting bolt in the left hand corner away from me.
    I know when that corner reaches a certain temp I am good to size.
    Don't like being hammered by the Cast Boolits Staff, then don't be a nail.
    The rules are simple to follow.

  12. #12
    Boolit Buddy Tmaloy's Avatar
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    I disassembled the grill lamp and ran a thermocouple line that came with my handheld temp reader I have for a mockup. I intend to use the probe that will come with the PID setup and run it through the inside of the of the gooseneck and mount the probe on one end. Both ends are threaded, metric as far as I can tell. I'm sure I can make a sleeve of some sort to have the T/C probe and gooseneck one piece. I may me able to mount the other end on the PID controller to keep everything together and be able to switch between both the 4-20 and Magnum Melter when needed.


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  13. #13
    Boolit Master Drew P's Avatar
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    Why do you want to avoid drilling the pot again? If it’s purely so you can move the pid around it would make more sense to buy another TC and just swap the wires instead. I don’t see how putting the TC underwater in the lead pot will be a good thing for it. Plus constant moving around and jostling is what will shorten the life to zilcho

  14. #14
    Boolit Buddy Tmaloy's Avatar
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    I don't have the short T/C, I will have the T/C that is coming with the PID controller that is the one HATCH supplies. I can use it and if I get the short ones in the future, I can try the internal pot mounting.

  15. #15
    Boolit Buddy
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    I just drilled a hole through the tin cover underneath the pot and secured the probe with a nut. Only the very tip of the probe touches the pot. I have about an inch between the spout and the top of the mold, so the mold never hits the probe. I've only had it on about a month, I've made about 5k 9mm boolits and it's been perfect so far.

  16. #16
    Boolit Buddy
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    This is my thermocouple setup. I cut approximately a 1" piece of 3/8" rod and tapped it to 10-32 then added a little piece of flat stock.
    Works well and I dont have to meddle with it.
    I can switch between pots or toaster oven for PC with 2 nuts.

  17. #17
    Boolit Buddy
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