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Thread: Bringing the Lee Hardness Tester into the digital age

  1. #1
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    Bringing the Lee Hardness Tester into the digital age

    So a while back I started mixing up 1:20 tin:lead alloy for my Sharps, 'cause some folks said it was the thing to do.

    I thought, "Gee, it would be nice to use wheel weights instead of tin, 'cause I have a lot of wheel weights and tin is expensive!"

    So, I got one of those Lee Hardness Testers. According to the web, it is among the most accurate. Basically, it's a little pocket microscope that has some lines etched in it that correspond to .002" increments on whatever you are looking at. It's got a little spring-loaded dimple maker you put in a regular press.

    Problem is, I could not hold the little microscope still to save my life. I found it almost impossible to count the number of tick marks to measure the dimple.

    So, I 3D printed a nice stand for it. But in addition, I printed an adapter so that I could mount a cheap USB microscope to it. It does not fully view the entire scale of tick marks, but it works very well. Now I can gently ease the thing into position and count the tick marks on the screen with ease.





    I'm not sure I'm getting great results just yet - my 1:20 alloy is measuring out for hardness like 1:30 alloy should, and I'm pretty certain about my alloy. Gotta do some more testing.

    Steve

  2. #2
    Jim Barber is offline
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    Steve,

    Great idea! When my brother and I are casting, we always test out the chunks first-- but we look like two monkeys having relations with a football. One of us shines a bright light on the chunk while criticizing the measurement-taker's poor skills with the microscope. Usually we trade places a couple times until one of us catches a glimpse of the elusive dimple & scale. It's always a debacle. Under no circumstances can you use the Lee Brinell Tester after drinking half a pot of coffee!

    Cheers,

    Jim B.
    Grove City, OH

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    LOL Jim great visual!

    Steve

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    Chris Sweeney is offline
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    The Lee tester works well but it is super technique-sensitive! I get 1/2 point differences on different measurements of the same ingot. The instructions want you to file a flat smooth area on your test piece - I always wondered if there wasn't a bit of work hardening going on . . .
    Chris Sweeney

  5. #5
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    It is my understanding that lead actually work SOFTENS, but yeah, maybe it does affect it somewhat. But then what happens when you size a bullet? I'm sure there is some minute affect, but probably negligible in the grand scheme of things.

  6. #6
    John Bly is offline
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    Like most metals, lead work hardens when squeezed, sized or hammered. However lead at room temperature is above the critical temperature which means it is self annealing over time. Alloying elements can change the characteristics of lead. I'm talking about the pure stuff we use for minies.

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    How much will hard lead harden over time? Does it peak-out in so many days?
    Mike 'Bootsie' Bodner
    Palmetto Sharpshooter's, Commander
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  8. #8
    John Bly is offline
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    Pure lead and lead/tin alloys soften over time. Alloys with antimony have different characteristics that I'm not familiar with as I don't use them.
    The following is by Dr. Glen E. Fryxell - From Ingot to Target, Chapter 3 - Alloy selection and Metallurgy

    Metallurgy of the Cast Bullet

    Lead-tin (Pb-Sn)

    Which metals do we add to lead to make better bullet metal and why? The first and most obvious need here is to make the alloy harder, but there are other factors that play into this answer as well. Historically, tin was used because it was readily available in pure form, mixed easily with molten lead and contributed desirable properties to both the molten and solidified alloy (castability and hardness, respectively). Tin also increases the hardness of the alloy but does not interfere with the malleability of lead (a key point that we‘ll return to). Tin lowers the viscosity and surface tension of the molten alloy, allowing it to fill out the mould more effectively, resulting in a higher quality bullet. Tin is limited in its ability to harden lead, achieving a maximum hardness of about 16 BHN at 40% tin. These binary lead-tin alloys undergo slight to moderate age softening upon storage (1-2 BHN units), with the harder alloys undergoing more of a change than the softer alloys. The hardness of a binary lead-tin alloy generally stabilizes after about 2-3 weeks. Heat treating binary lead-tin alloys does not provide any change in hardness. At typical lead pot temperatures, lead and tin are infinitely miscible with one another, at the eutectic temperature (361o F) tin is still soluble to the tune of 19%, but at room temperature tin is still soluble in lead at the 2% level, meaning that as the bullet cools down there is significant precipitation of a tin-rich solid solution in the form of granules and needles in a matrix of lead-rich solid solution. It is important to recognize that tin is well mixed in the matrix and it hardens lead by making the matrix itself harder.
    Last edited by John Bly; 02-16-2019 at 09:31 AM.

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    John Bly is offline
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    Here's more than you probably need to know about antimony alloys.

    Lead-antimony (Pb-Sb)
    Antimony on the other hand hardens lead alloys much more efficiently, with only 1% antimony producing a BHN of 10 while it takes 5% tin to do the same, and it takes only 8% antimony to achieve a BHN of 16, as compared to 40% tin. The name "antimonial lead" refers to binary lead alloys with 1-6% antimony, with the higher antimony alloys (i.e. those with >1% antimony) commonly being called "hard lead" in industry. While antimony increases the hardness of lead, it does so by impairing its malleability. At typical lead-pot temperatures (ca. 700o F), antimony is only moderately soluble in lead alloys, and as the temperature drops, the solubility of antimony is markedly lower than that of tin. At the eutectic temperature for a binary lead-antimony alloy (484o F), only 3.5% antimony is soluble (note that this is 123o F hotter than of the tin eutectic temperature, but the antimony solubility is less than 1/5 that of tin). At room temperature the equilibrium solubility of antimony in lead is only 0.44%. The precipitated antimony appears as small rods, at the grain boundaries and within the grains themselves. Electron micrographs of lead-antimony alloys clearly show discrete particles of antimony surrounded by a matrix of lead-rich solid solution. In contrast to lead-tin alloys, lead-antimony alloys age harden, sometimes as much as 50% or more. When these alloys are air-cooled, some antimony is retained in the lead-rich matrix and as a result these alloys age-harden as this antimony continues to slowly precipitate. This usually takes 10-20 days to achieve full effect.

    It is important to recognize the antimony hardens lead alloys by a fundamentally different mechanism than does tin. Antimony hardens the alloy by precipitation of a separate crystalline antimony phase, which reinforces the squishy plastic lead phase that’s in between the hard antimony crystals. These alloys tend to be brittle because the plastic (squishy) lead phase gets its hardness from the reinforcing hard antimony rods. As the matrix gets deformed the brittle antimony rods shear off and the soft metal fails. In the case of the lead-tin alloys, the tin is more uniformly distributed through out the matrix, making the matrix itself harder, so plastic deformation of the alloy is more uniform and progressive, not the slip/shear of lead-antimony alloys.

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    This is the lead tester that I use. It is very simple to use and very accurate.

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    Mike Santarelli 03635V, Adjutant
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