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Thread: Cheap K type thermometer

  1. #1
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    Cheap K type thermometer

    I'm sick of overheating aluminium and getting hydrogen porosity. Since we don't have McMaster-Carr here in Europe, I am having a go at Raspers Thermometer (it is not a Pyrometer as it is not optical right?) using cheap parts.

    I have already received the K-Type thermocouples from China. At €3.14 a piece, I ordered 4 to have spares.
    http://www.ebay.at/itm/291156009222?...%3AMEBIDX%3AIT

    The graphite rods came from the Ukraine. They also arrived yesterday, along with a Diamond grinding wheel for my Clarkson T&C grinder, and some diamond honing paste to hone my carbide scraper.
    http://www.ebay.at/itm/281984894120?...%3AMEBIDX%3AIT

    Instead of a Multimeter, I'll invest the €5 for a digital Thermometer Display.
    http://www.ebay.at/itm/Neu-Digital-L...cAAOSwoydWkxtm

    Mark

  2. #2
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    I googled "pyrometer" and wiki implies that it's any remote sensing temperature measuring device.

    Interesting choice in thermocouple. Be sure to post results of the build.

  3. #3
    I use exactly the same thermometer and K thermocouple. The stainless steel probe melted after all these melts but i still use it and the reading is instant.
    I found that trying to find what I need and then make it work with what I have, is more trouble than designing what I want and doing it.
    me

    "Quick decisions are unsafe decisions."
    Sophocles

  4. #4
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    Dude, thanks for clarifying that. I was under the misunderstanding that Pyrometers used optical means.

    3D, Did you not shield it in a graphite rod, but just dunk the stainless tip straight in the Alloy? At €3.14 a probe, not a bad choice if they last a few casting sessions. Then again, since I already bought some graphite rod, and like solving simple problems with complicated solutions which involve the lathe, I'll probably still shroud them. The probes are really quite nicely made. I was surprised someone in china can make a profit selling something with so many parts, including postage, for so little dough.

    Mark

    Mark

  5. #5
    I was surprised at their price as well at 4.8 euros back then, so i bought two in 2014. I suggest you shield them and don't go as i did, although it lasted maybe a couple years before it dissolved. I still use it as it is and didn't replace it.
    I found that trying to find what I need and then make it work with what I have, is more trouble than designing what I want and doing it.
    me

    "Quick decisions are unsafe decisions."
    Sophocles

  6. #6
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    The things to keep in mind when drilling the graphite rod are:


    • Make the hole a tiny bit larger than your probe. The graphite rods break easily.
    • Stop drilling about 3/4 inch from the end of the rod.
    • It is important to drill the hole in exactly the center of the rod.
    • Molten bronze dissolves the graphite gradually. (I don't know about aluminum; I don't do AL.) It is best to drill several rods for future use while you are set up for it. They are easy to break if dropped or hit.


    Richard
    When I die, Heaven can wait—I want to go to McMaster-Carr.

  7. #7
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    Thanks for the inputs. Graphite sure machines easily. Chopped the electrode in two on the DoAll, then faced it and did the drilling on the lathe, and also cut an M8 thread in the end to pick up the thread on the thermocouple. The taper on the end is just to make it look finished. The handles are just some zinc plated 1.5 mm wall, water pipe, with a bit welded to the tip, and washer welded on for the probe to mount to. Welded them with skinny little 1.5mm electrodes at 50A. Kind of a differcult to weld, especially if you are a crap welder like me.

    I tested the probes with the mutlimeter. Now I am just waiting for the thermometer displays from china, and I'll probably fold up a little sheet metal box to hold them to the handle.

    I made two, one for me, and one for Franz, who I have been casting with lately.

    Mark
    Attached Images Attached Images

  8. #8
    Nicely done Mark! Do tell me how it performs, i'm interested to see if i should change mine.
    I found that trying to find what I need and then make it work with what I have, is more trouble than designing what I want and doing it.
    me

    "Quick decisions are unsafe decisions."
    Sophocles

  9. #9
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    Probably be a couple of weeks till the displays arrive on the slow boat from China. I'll post once we try them.
    Mark

  10. #10
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    The only thing you have to account for if you use the multi meter for a pour while you are waiting for the slow boat is that your are not measuring absolute temperature, but the difference between the temperature of the probe and the temperature of the multi meter. You purpose-built digital readout should account for that automatically.

    Richard
    When I die, Heaven can wait—I want to go to McMaster-Carr.

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