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Thread: Flame Hardening

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    Default Flame Hardening

    I would like to understand more about the metallurgy behind flame hardened lathe beds, also the process itself (is the bed preheated, how is the heat regulated, how deep does the hardness go, is the flame followed by an oil quench or is it just an air-hardening process). And lastly, if a flame-hardened lathe bed is re-ground due to wear, will it require re-hardening, and if so, does anyone offer that service?

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    All the demos I've seen, the part starts at room temperature, there is an array of flame nozzles with controlled motion that move from one end to the other, and there's almost always a flood water (might be a synthetic quenching fluid, but I doubt that's common) quench that follows the flame at a fairly short distance. Travel speed is adjusted to bring the ways to the desired temperature at the desired depth.

    Hard case depth varies a lot with the parameters (e.g., travel speed) the manufacturer chose, but 0.025" to 0.040" before finish grinding would be a reasonable range. That means a moderate regrind job may preserve some of the hardened case.

    Whether rehardening is "required" would depend an awful lot on the specifics of the machine involved and how many years additional use, and the severity of expected use. I'd generally say "not required", because if you plan to put another 3 to 5 decades of hard labor on the machine, you're probably better off buying a new and/or additional machine. If the machine is being reconditioned for a home or recreational shop, the answer is "absolutely not required".

    There is probably someone who can make a stab at flame-hardening for you, but it's not a common service, and unlike the original manufacturer they certainly have not dialed in their procedures on your specific model of machine. So, some risk involved. If the original manufacturer is still in business, and if they recondition their older machines, probably best to send it to them.

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    Check out page 5 on hardened bed ways. http://vintagemachinery.org/pubs/2103/19731.pdf

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    Quote Originally Posted by rimcanyon View Post
    I would like to understand more about the metallurgy behind flame hardened lathe beds, also the process itself (is the bed preheated, how is the heat regulated, how deep does the hardness go, is the flame followed by an oil quench or is it just an air-hardening process).
    This is an interesting old video that many people here have seen before, "The world turns on Colchester lathes":



    Starting about 6:20 in, you can see the hardening process for the lathe bed. They use an induction heater that moves along the top of the bed, with an integral water quench.

    What I find funny in this video is that many of the production machines were finished with gold-colored paint, presumably for the filming.
    Last edited by ballen; 04-24-2021 at 01:48 PM.

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    Quote Originally Posted by ballen View Post

    What I find funny is this video is that many of the production machines were finished with gold-colored paint, presumably for the filming.
    I'd commented on the gold paint in an earlier thread about that video, and someone made the point that it could be from colorizing of the video rather than the actual color used by the factory. If anyone knows for sure it would be nice to have confirmation one way or another.

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