How do you treat a watch spring to keep it’s shape?

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  • #48411
    ptheys
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    I have a hampden watch with a odd shaped spring.I have material for watch springs. I can make the shape, but how to keep it, harden it. It stretches out fast. This is one of my favorite watches.I have tried heat treating with a flame but I must be doing it wrong. Any help is appreciated.

    #52373
    Bob Tascione
    Moderator
    • Topics Started: 38
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    Welcome the the forum Paul!
    Distortion is a real challenge when dealing with heat treating springs. I like to use oil hardening steels for springs. This is steel with a carbon content of 1 to 1 1/2 percent. Oil hardening steel is good for me as it accepts a slower cooling time than water hardening steel which usually means less tendency to distort and yet can still hold a nice deep looking polish. There are also air hardening steels that are great for eliminating distortion but have proved difficult for me to get a decent polish out of such as that deep black polished look that so many of the high end watches have.

    Thin steel pieces such as springs when cooled abruptly will tend to distort. For long straight or relatively straight but uneven pieces I make a sheath out of iron binding wire which is longer than the part to be hardened. I just wrap the wire around different sized watchmakers screwdriver handles to get the necessary shape depending on what size I’m after and then drop the piece into the sheath and heat the sheath directly. This keeps the flame off of the part which is really important if you don’t want it to warp (best way is to used a heat treating oven but…). The entire sheath can then be dunked when the required heat has transferred to and through the part. For parts such as the one you show in the pic I have a bunch of different sized copper boxes that I’ve made. Most are just round boxes that I made out of copper round stock with simple copper caps. The part can be heated and cooled the same way as with the iron sheath. If the part is really thin and sensitive I put iron filings into the box with the part to help distribute the heat more evenly. Another thing that works well is just wrapping a bunch of turns of the binding wire around the part and then go through the same heating and quenching process as above. This works very well if the part has some strength but is risky when working with thin springs as applying the wire can bend the part and removing the wire can break it.

    It’s also important to know the characteristics of whatever metal you’re working with. Some require more heat than others to harden. So testing the metal first is a good idea before making parts from it.

    Well, hope this helps Paul,
    Again Welcome,
    Bob

    #52374
    ptheys
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    I don’t see the picture you refer to.I do have brass shim stock or 1/4 copper pipe with caps and lots of metal shavings. So if I made the spring and put the pipe with metal shavings. Heated it. (how Hot?) then dunked it in oil to cool (used motor oil?) Or would be better to fold the spring in .01″ brass shim stock with some metal shavings and go that way? Thanks for the help.

    #52375
    Bob Tascione
    Moderator
    • Topics Started: 38
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    Hi Paul,
    Sorry, when I mentioned the pic I was referring to your pic of the spring.

    You could test in the shim stock with a piece of wire or material you’re making the spring out of to see if you get the hardness you’re after. It’s certainly worth a try. Brass has a slightly lower melting point than copper so may burn through that .01 shim if not careful. I usually wrap my copper boxes with iron binding wire and watch the color of the wire as well as the copper. Generally I bring the box and wire to a cherry red (shade depends on past results with type of steel) and keep it in the flame long enough for the heat to transfer into the part. If the box or your shim wrapping is just slightly larger than the part inside, the heat will transfer into and throughout the part very quickly. Extra space inside isn’t a good idea as cooling may not be quick enough for the part when quenched.
    Motor oil works well in most cases for watch parts. Also thinner vegetable oils or olive oil is good. When heat treating parts by hand the color and heat transfer time is more or less a judgement call based on experience with the steel and technique you’re using. It appears rather primitive to machinists/toolmakers who heat treat steels using ovens and industry quenching oils. An oven can be set to the exact temp that is recommended for a particular steel and the length of time to leave it in the oven can be determined by the area of the part or parts being treated. Whereas making watch parts is much more ‘hands on’ and timing is everything. That’s the fun part though and once you’ve done it a few times the success rate really gets up there!
    Again would be a good idea to test a few pieces first. Test, test, test…
    A few tests should reveal the best way to go about it.
    Please let us know how you do it and the results before and after you’ve tempered it Paul,

    Good luck and have fun!
    Bob

    #52376
    david pierce
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    • Topics Started: 90
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    Ptheys,
    Springs can and often are wound from prehardened, pretempered steel such as music wire. Flat springs are also made this way but due to the hardness of the spring steel (RC 47) they are difficult to machine and are usually stamped.
    david

    #52377
    ptheys
    Participant
    • Topics Started: 2
    • Total Posts: 6

    :D I made a spring and it holds it’s shape. I kept going back to it during the day to check on it. I used .050″ sheet metal to make the three disks and drilled one out. I put the springs sandwiched in the disks with some very tiny metal fillings. Wrapped in .30″ safety wire. Keep turning it as I heated the wire to a cherry red. Cooled in vegetable oil. Beginners luck?


    #52378
    Bob Tascione
    Moderator
    • Topics Started: 38
    • Total Posts: 1552

    Hi Ptheys,
    That’s not beginners luck at all but rather good thinking on your part! I like your idea of making that washer to put the part into.
    Thanks for the follow up. That spring looks great…Congratulations!
    Bob

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ptheysHow do you treat a watch spring to keep it’s shape?