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    Leaf spring prod stiffening

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    Zardoz
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    Leaf spring prod stiffening

    Post by Zardoz on Thu Nov 15, 2012 7:37 am

    I have an idea for strengthening the center hole of a leaf spring. First, take a Dremel with a grinding stone and lightly chamfer the outer edges on both sides. Next, cut a disc of drill rod, tool steel, or some other hard steel a little thicker than your spring. Next, if available, coat the area around the hole with heat sink compound (available at a welding supply place). Next, heat up the disc on a safe surface till it is bright orange. Put the spring on an anvil and drop the disc into the center hole. Using a small sledgehammer, quickly hammer the disc till it's flat and fills the hole tightly, then quickly quench in water to retain temper. Now grind both sides flat to the spring, quenching as you go. I feel that this method should keep the belly side from compressing and the back would be only under tension. I will be using a 1 3/4" wide by about 26-28" 1/4" thick utility trailer spring for this experiment. What do you folks think?

    8fingers
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    Re: Leaf spring prod stiffening

    Post by 8fingers on Thu Nov 15, 2012 4:50 pm

    If you go to a spring shop you can get springs without holes.
    Your technique seems sound but I wonder if your plug might act more like a knot in a board. Also the steel plug will expand as it is heated, contract as it is cooled , possibly leaving it slightly loose in the hole. I think silver solder might be a better approach as it has a low melting point, and wouldn't get hot enough to endanger the temper.
    I am looking forward to replies from those with engineering backgrounds.
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    Zardoz
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    Re: Leaf spring prod stiffening

    Post by Zardoz on Thu Nov 15, 2012 5:02 pm

    I like the silver solder idea, but metal must be cherry red to silver solder and that might ruin the temper. I do have 2 spring shops near me and I was going to ask them about the hole-less springs next time I am in the area. You mean silver solder, not electrical solder, right?

    8fingers
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    Re: Leaf spring prod stiffening

    Post by 8fingers on Thu Nov 15, 2012 5:20 pm

    Silver solder comes in different temperature ranges, the lowest temp solders. A quick check of Jantz Knife making supplies shows some solders with a melting point of 425 *F
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    Zardoz
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    Re: Leaf spring prod stiffening

    Post by Zardoz on Thu Nov 15, 2012 5:27 pm

    Good, I think the spring temper is somewhat over 600 degrees.

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    Re: Leaf spring prod stiffening

    Post by panne on Fri Nov 16, 2012 6:15 am

    carbon steel starts to lose temper at 400*F. if you heat the plug and then hammer it in, it's mass should likely be small enough that it will not effect the temper of the spring, since the springs mass would quickly cool the plug. the plug doesn't need to be heat treated, but should be of a decent enough quality that it will support the hole area and not warp under tension when spanned. you may still need to add a cover plate to stop it from flexing in the center causing the plug to loosen.
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    Zardoz
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    Re: Leaf spring prod stiffening

    Post by Zardoz on Fri Nov 16, 2012 6:32 am

    That is exactly what I was thinking of. I was going to try a tight fitting plug of hard steel thicker than the spring and grind down to the pre chamfered hole after hammering. I figured that the spring mass and quenching would preserve the temper.

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    Re: Leaf spring prod stiffening

    Post by panne on Fri Nov 16, 2012 1:34 pm

    a large steel rivet the same size as the hole should work. if you put the head on the outside, you can hide the hammered side in a shallow hole behind the prod without grinding, which would weaken the rivet.

    i'd test pound one to see if you can get it hammered out evenly before it cools. if all goes well it shouldn't take more than 2 or 3 hits with a center punch. you may not have to heat it at all if you have a good anvil and a big enough hammer and punch. it all depends on the hardness of the rivet and who's swinging the hammer.
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    Zardoz
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    Re: Leaf spring prod stiffening

    Post by Zardoz on Fri Nov 16, 2012 2:05 pm

    I was thinking i could hammer it cold if it is mild steel. I have a 200lb anvil at work and am no stranger to a hammer. I thought about the chamfered holes to avoid having a lump on the bow. But I agree that the lump would make it stronger and would not be seen in a recess.

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