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Shortening A Spring Using Heat

  • 26-08-2009 04:56PM
    #1
    RabidDog
    Closed Accounts Posts: 143 ✭✭


    Hey guys,

    Now first a disclaimer. This worked for me, but it could have been a fluke. Also as it was only done today, I'm not sure how the long term performance would be affected, the spring may be weakened and so drop in power faster and if the spring warped there is a chance that the internals could be damaged.

    Also I know it's easy to order replacement springs, and they aren't too costly, but please don't comment on how I should just order a new spring.

    I'm sure this has been done before, but I thought I'd let ye know how I did it and how I got on.


    Ok so I ordered an Element M95 replacement spring for my D-BOYS HK416 import, which was shooting at ~350FPS. The M95 was too powerful however (~340FPS) and so I tried cutting the original spring which came with the HK416. That was a failure however, because the end of the spring was warped by the snips and I couldn't get it straight by heating and bending.


    So I removed the M95 spring and measured it. Then I heated it over a gas flame (I used a camping stove) until red hot and pressed it into a piece of wood until it cooled. The effect of this is that when the metal cools it sets slightly shorter. I had to do this twice to get the overall length down by around 8mm. The second time I heated slightly further up the spring, to avoid having the coils too close together.

    It is best to use wood to compress the spring against because it insulates against the heat. Pressing the hot spring against a metal surface would cause it to cool faster. Also be careful when compressing the spring, if it is warped while cooling the spring will end up bent. I've considered screwing a cylinder of wood into the piece of wood I'm pressing against to act as a spring guide, to stop it from bending (I have a few AEGs to do for other people).

    Once I was happy with the length, I heated the end of the spring again and dipped it in water. I repeated this once more in hopes of tempering the metal, though I don't know if it makes any difference.


    After the above process the HK416 now shoots as a steady ~310FPS. :)


    I'll be using this process on two or three other AEGs during the week, and they'll be used thereafter, so I'll post here and let ye know of my results.


Comments

  • #2
    Frank the Manc
    Registered Users, Registered Users 2 Posts: 947 ✭✭✭Frank the Manc


    I dont know the disadvantages of using heat to weaken a spring but im sure others more qualifies to comment will, but iv found when cutting springs a bout 2.5 coils off a 360ish spring will bring it down to 310-320.

    You should grind the end of springs on a bench grinder to flatten them, you may see this process on lower end springs wher the metal has discouloured and the end.

    Yeah the Element M95 springs will be over alright, ive even found m90 springs may be slightly or inconsistently over in Ver 3 gearboxes initially, but they usually settle down after bedding in.


  • #3
    RabidDog
    Closed Accounts Posts: 143 ✭✭RabidDog


    That's a good idea, and I do have a bench grinder. :)

    This is more of an experiment to see if it (heating and compressing) works and what the drawback are. I'll definitely be ordering replacement springs in the no so distant future.


  • #4
    Masada
    Banned (with Prison Access) Posts: 11,001 ✭✭✭✭Masada


    your idea is sound, the only thing i wouldnt do is to water cool it as you slightly harden the metal and harder metal is more brittle metal.

    Its quicker and easier to cut the spring though as frank said, you usually get maybe 10-12 fps per coil (depending on spring obviously) and as long as you round the end nicely and don't make the spring too short for the stroke of the gearbox you'll be fine., :)


  • #5
    Firekitten
    Registered Users, Registered Users 2 Posts: 4,205 ✭✭✭Firekitten


    and for gods sake... take the coils from the NON tightly coiled end... :D


  • #6
    RabidDog
    Closed Accounts Posts: 143 ✭✭RabidDog


    Masada wrote: »
    your idea is sound, the only thing i wouldnt do is to water cool it as you slightly harden the metal and harder metal is more brittle metal.

    Its quicker and easier to cut the spring though as frank said, you usually get maybe 10-12 fps per coil (depending on spring obviously) and as long as you round the end nicely and don't make the spring too short for the stroke of the gearbox you'll be fine., :)

    Good to know about making it brittle.

    To be honest I think this is much easier than cutting, as you are not changing the shape of the spring's end (from | to /).

    If the spring is cut what is the best method of doing so, snips or hacksaw? And what is the best way of flattening the end (from / to |)?


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  • #7
    Skatedude
    Registered Users, Registered Users 2 Posts: 2,674 ✭✭✭Skatedude


    using heat to shorten a spring is a definate no no, spring steel is heat treated and hardened very specificly, if you re heat it you will affect its properties,
    cutting down would be the best solution next to replaceing the spring out right,


  • #8
    RabidDog
    Closed Accounts Posts: 143 ✭✭RabidDog


    Good to know, thanks Skatedude.

    I'm not worried in this case though, the spring would have been thrown out anyway.


  • #9
    Stercus Accidit
    Registered Users, Registered Users 2 Posts: 8,758 ✭✭✭Stercus Accidit


    I used to do a similar thing as an experiment, but to raise fps by tempering certain materials of springs.

    For a down grade a snips is best.

    Put the cut end in the piston, and use a pliers to coil the cut end slightly tighter so it doesn't scrape the inside of the piston, and I usually file down the sharp end til its smooth so it just spins and doesn't scratch in place.


    You can also get a knack for guessing how much to take off and get a desired fps under the joule limit.


  • #10
    RabidDog
    Closed Accounts Posts: 143 ✭✭RabidDog


    Stercus Accidit wrote: »
    I used to do a similar thing as an experiment, but to raise fps by tempering certain materials of springs.

    Ah, a novel idea. Did it work? :)


  • #11
    Stercus Accidit
    Registered Users, Registered Users 2 Posts: 8,758 ✭✭✭Stercus Accidit


    RabidDog wrote: »
    Ah, a novel idea. Did it work? :)

    On some metals of springs, others no.

    It was too much hassle compared to other ways to raise a low fps, bearing spring guides, spring buffers etc.


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