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I Forge Iron

Testing laser thermometer for heat treatment


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[MOD NOTE: The following thread started out on the "It followed me home" thread, but is moved here to accommodate the discussion of testing and calibrating that started a few comments in.]

Another mail call! Invested some of the money from my last commission in an infrared thermometer (goes up to 2,732°F/1,500°C) to take the guesswork out of heat treating. 

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It’s an “ANNMETER AN-1500” from Amazon, but there are a whole bunch of different brands that are basically the same. This one was a decent price for the temperature range I wanted. 

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Have one from Hobo freight, probably same model with a different decal. I compared the temp read out with a name brand (think it was a Fluke) where I work. Surprised me when the temps read within a degree of each other, problem is they don't read high enough for a forge temperature.

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1 hour ago, lary said:

problem is they don't read high enough for a forge temperature.

Mine is supposed to read up to 2,732°F/1,500°C, but I doubt I'll need to get quite that high!

I'm thinking about how I can test mine by measuring different substances at known high heats. Obviously, water boils at 212°F/100°C. I think the following melting points might also be helpful:

  • Boric acid (H₃BO₃): 339.6°F/170.9°C (the main ingredient of Roach Prufe, although minute quantities of the other ingredients might throw things off a bit)
  • Lead (Pb): 621.5°F/327.5°C
  • Table salt (NaCl): 1,474°F/801°C
  • Borax (Na₂B₄O₇): 1770ºF/966ºC
  • Copper (Cu): 1,984°F/1,085°C (assuming I can get this high in my gas forge; I think I can, but I've never tried)

Any other suggestions?

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Here are some other metals I might try:

  • Aluminum (Al): 1220°F/660°C 
  • Sterling silver (Ag + Cu): 1634°F/890°C (I've got some old jewelry from my mother-in-law's estate that no-one wants)
  • Cast iron (Fe + C + other stuff): 2200°F/1204°C

I could probably get some zinc (Zn; 787°F/420°C) easily enough, but I don't want to be breathing any zinc oxide fumes, thankyouverymuch.

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The breeder who developed the Carolina Reaper has developed a pepper (called "Pepper X", 3.18 million Scoville Heat Units) that he claims is twice as hot as the Reaper (1.5 million SHU). Another breeder in Wales has developed a pepper with 2.48 million SHU whose name would be quite appropriate for blacksmiths: the Dragon's Breath!

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Test it on your arm, leg, forehead, or where ever then take you temp and see is it matches. Also on ice. That will give an idea of accuracy of low temps. I have not used one in years but i know they used to have curve on accuracy. That had a sweet spot where they were quite dependable but the further above or below that temp would be off. Bell curve i guess. Also distance from what you are checking is important. Another thing is color of what you are checking. Shiny metal can reflect IR heat back into the thermometer and give a false reading.

I too will pass on those peppers. 

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One nice thing about this model is that it has two lasers that converge on a point about 30" out from their lenses*, so that it's easy to get the same distance every time.

*I'll check later when I get home from work.

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Did a little preliminary testing yesterday, heating up a piece of plate with the torch and comparing the thermometer with a 600°F Tempilstik, table salt* (1,474°F), and borax (1,770°F).  

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The results were a bit inconsistent: I was just heating one spot, and the steel was cooling down a bit as I juggled the torch and the thermometer. Nonetheless, all three measurements were pretty close, and I’m looking forward to doing some more controlled tests later. 

* Technically kosher salt, which may actually be a bit better, as it doesn’t have the iodine (sodium iodide or potassium iodide) or anti-caking agents found in table salt. 

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