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  1. #1
    Join Date
    Aug 2006
    Location
    Melbourne
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    47
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    Default Hardening nail punch

    G'day all,

    I've been reading a little about heat treating steels like O1 and M2 tool steels and managed to learn quite a few things about how to harden steels. Now that I have an idea how I can manage this at home, I would like to have a go at re-hardening a nail punch I made some years back.

    OK, I helped a mate with his deck by making him a nail punch with a fat head on it; simply a cold chisel ground to shape with a section of 6mm steel plate welded to the top so that he was able to give it a good whack without fear of bashing his hand with a 5lb hammer. All is well until about the 10th nail when the punch point has flaired to the point of damaging the decking timber.

    At the time I couldn't fathom why this would happen because I'd choosen the cold chisel for it's hardness. Now that I understand how I've damaged the temper through grinding the cutting the tip I'd like to have a go at re-hardening the tip to make it useful again.

    So, two questions:

    1) can anyone tell me roughly what carbon content I can expect to find in a steel used to make a reasonable quality cold chisel? This will help me determine both the hardening temperature and the optimal tempering temperature.

    2) Can anyone give me an idea what sort of hardness I should aim for with respect to a device used under the constant impact of a large steel hammer? Too soft and it will flair again, to hard and I might break off the tip or something.

    Thanks all for your assistance.
    "Human beings, who are almost unique in having the ability to learn from the experience of others, are also remarkable for their apparent disinclination to do so."
    - Douglas Adams

  2. #2
    Join Date
    Nov 2006
    Location
    kansas mostly
    Posts
    33

    Default

    With any unknown steel, unless you get a metallurgy analysis done, you really don't know what you have. For a cold chisel I would guess the steel would be something in the S series (maybe S5 or S7).
    I would thing it would be somewhere in the mid carbon range; maybe 60 or 70 points carbon. But that is just a guess based on what I would use.

    Are you familiar with the spark test? Different carbon content and alloying elements change the way a steel sparks when taking it to a high speed grinder.

    As to what to temper to, I'd start in the neighborhood of 55 - 57 HRc and see how that works and adjust as needed.

    ron

  3. #3
    Join Date
    Aug 2006
    Location
    Melbourne
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    Default

    I've done a little research and a medium carbon content seems to be the general recommendation for this sort of application. 'Blue' tempering around Rc57 seems to be the norm also.

    This is a good start, at least I can give it a go with this or this
    "Human beings, who are almost unique in having the ability to learn from the experience of others, are also remarkable for their apparent disinclination to do so."
    - Douglas Adams

  4. #4
    Join Date
    Aug 2004
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    Lost in Space
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    53
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    331

    Default

    Gidday

    Cold chisels are usually low carbon steel with the blade end being hardened through heat treatment.

    The entire chisel is not hardened to reduce the overall brittleness so that burrs n shards of metal dont get fly off the chisel after a heavy strike.

    So its really important to just harden the blade end of the chisel!

    Heres a handy article thats a good primer .............

    http://www.anvilfire.com/index.php?b...0anvilfire.com

    I suspect the same process would be applied to things like punches too............would be great to hear how you end up approaching this one!

    Regards Lou
    Just Do The Best You Can With What You HAve At The Time

  5. #5
    Join Date
    Sep 2007
    Location
    Sydney
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    61
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    Default

    A cold chisel and a nail punch have similar applications so you should be able to re harden and temper the nail punch that has been made from a chisel.
    I did the same recently and remembered back to year 8 or 9 when I made a punch and chisel set in metalwork, I still have them and have used them many times.
    You will need a heat source, like a good gas burner or oxy/acetelene, an old soup tin or similar 2/3 filled with engine oil (used is ok), a piece of emery paper, a bucket of water, a pair of pliers or multi grips and a pair of leather gloves.
    It also helps if you can place a couple of dry bricks or a piece of fibro to help with heating evenly but this can be done with moving the tool round in the flame to get an even heat.
    So, set up the area with heating torch, beside it the oil and the emery paper, then beside that the bucket of water.
    Hold the job with pliers or multigrips and heat the tip of the punch about 40 to 50mm up to cherry red, make sure the heat is penetrating the steel and not just on the surface. Move it round the flame to get an even red colour over the whole surface.
    Now dunk the job into the oil but don't drop it in. Expect much smoke and possibly flame from the oil (that's why the gloves). Keep it in for a few seconds and pull it out.
    Quickly rub the blackened surface 20 to 30mm from the point with the emery paper and you will see the temper colours appear. When it is a straw colour dunk it back in the oil for 20 to 30 seconds then into the water to cool it right off.
    Job done, go and test it.
    If it is too hard it will chip or crack, if it is too soft it will deform. Either way, reshape it and do it again.

    Do not be tempted to quench the job in water not oil, it will cool the job too quickly and may cause cracking on the surface or internally.

    Good luck and let us know how you go.
    Cheers

    Alan M

    My Daughter's food blog www.spicyicecream.com.au

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