Testing spear shaft hardness DIY

  • Matt, I use 62 to 63 inch shafts. A bit shorter than 1.7.

    It does seem to be a grouper thing. I've shot a lot more snappers than groupers but they hardly bend shafts even though a dog will almost always try to hole up. Of course, any cubera larger than 20 lbs can do some damage too.

  • I missed this dialog, I use my Hardness Tester to verify my heat treating process is correct. It comes in ready handy when you go start drawing back the hardness of the metal.

    If the metal is too hard, it will be too brittle and snap. Thusly the annealing step. This is more about other metal types that you wouldn't use on a spear. Think of forming Dies, Crimper jaws and other tools.

    I measure deflection like Gecko does. Think of a graph, Lbs force vs distance. I tossed my POS Spring scale and bought a force gauge. This was big league improvement on numbers.

    Dan, you are going for the Yield Point. I tend to keep the test in the elastic region. and you can use Hooke's Law. Comparing test data to theoretical is always nice. You might also be chasing the vendors' shafts that was processed in different batches. I've seen some junk come thru the shop. Vendors you would not expect.
    Clean bench, impressive. Mine is terrible. You don't fold and iron your socks now?

    I'll post more information later.

    The post was edited 1 time, last by Linghunt: spelling ().

  • I have done a bit more thinking and reading on this subject and perhaps Dan is actually doing it the right way.
    My argument for not putting a permanent bend in the spear was two-fold. I thought there was no need, I was thinking/hoping that if the metal was stiff initially, it would be less prone to bending, too. Also, I don't really shoot big spear-bending fish but I would like a shaft which would suppress spear whip the most and thus be more efficient.

    As John explains in the previous post, up until the point of permanent bending, you are measuring the elasticity (the shaft will return to its original shape) but here is the kicker: This is pretty much the same for the different kind of steels we use! They will all, for a given thickness and force, bend the same amount. Up until the point where the will stay bent - that point can be vastly different and is the Yield Point given by the Yield Strength.

    So, for my hope of finding a spear which will whip less (whipping is elasticity as the shaft will return to normal), it's a futile test - they will all whip the same, they will all bend the same amount but some of them can take a lot more bending before they stay bent (and this is what Dan was setting out to test).

    So, Dan - please do continue the testing.
    With the usual disclaimer that I am not a metallurgist nor an engineer, if my findings so far are correct my test actually made very little sense and the only thing we really need to talk about with shafts is the Yield Strength. Unless, there are some steels out there with higher modulus of elasticity as this would make it whip less.

    The post was edited 2 times, last by Diving gecko ().

  • Any results yet? I'd love to know between riffe, hammerhead, pathos and beuchat although I am sure some of these are actually rebranding the shafts.

  • My main purpose is to compare stainless steel shafts from different manufacturers at the same diameter, most important to me is 7mm. If the results vary then obviously the steel used is different, or perhaps the process ie whether they were properly heat treated. That doesn't mean I'll know what kind of steel gives what results, unfortunately I don't have faith in stated specs. This is empirical testing. Once I find the strongest shaft it will become my benchmark.

    It's interesting to find out other things too, like if carbon steel shafts are really stronger than stainless at the same diameter. Or if a 6.5mm carbon steel shaft is as strong as a 9/32" US shaft.

    Very interesting test Dan but Your results will most likely vary even among the same manufacturer.

    Our shafts typically test out between 41-44 on the rockwell scale despite the fact we use aircraft quality, certified, center-less ground, American made 17-4 steel and have our own digitally controlled oven.

    17-4 stainless steel is SUPPOSED to be approximately 17% chromium and 4 % nickel.

    But, if it's not "certified", who knows what it is?!

    I have seen shafts (that were supposed to be 17-4 heat treated) test out softer than non-heat treated 17-4!

    Inexpensive steel as well as foreign steel is often way different than it should be and will often vary widely from batch to batch.

    A manufacturer may have a batch that turns out pretty good and the next can be twisted garbage that is way softer than it should be.

    Many shaft manufacturers bundle and send out their shafts to commercial ovens (for heat treatment) where time and temperature are a serious issue.

    This is very very common by the way...

    In addition, Inexpensive/foreign steel almost always contains unacceptable amounts of contaminants and this will result in a shaft becoming inaccurate way sooner than it should as it will get micro bends/twists from repeated use at it hits rocks, wrecks and bony fish.

    The post was edited 2 times, last by RichT ().

  • i m waiting for the results of spring steel (rob allen,spearmaster etc ...)its critical when u have to buy thick stainless like 8mm but u can use 7.5 spring instead and save a lot in my place ,is it true 7mm spring have similar stiff to 7.5 stainless ?getting stiff low weight spear help to reduce recoil and cost.

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