Testing spear shaft hardness DIY

  • Maybe testing shaft hardness is a misnomer, I'm less concerned with how hard a spear actually is than how bend resistant it is. More fish have been lost because of broken shafts than bent shafts, and who wants a bent shaft anyways. Also this is comparative testing, measuring shafts against each other, not a standard test. But after enough shafts tested you can develop a standard. I came up with this test because I didn't believe the hype about certain shafts and wanted to know for myself, and feel it's a real world test, the results tell me exactly what I need to know. So here's what you need:


    1. Vice attached to something solid.
    2. Tape measure.
    3. Fish scale
    4. Shafts or straight pieces of shafts at least 50cm long.


    The shaft gets clamped hard in the vice. The distance from the top of the vice jaws to the flopper pin hole is 40cm. I chose 40 cm because it seems like a reasonable length of shaft that could get torqued on in a spearfishing situation, and will not be extremely difficult to bend in the test situation. You can choose whatever length you want if there's a good reason for it, it just has to be consistent for all the shafts.




    The flopper should be facing directly away from the pull direction, this way it will trap the hook of the scale and the scale will not slip off the shaft. It will also allow you to quickly check for the bend because you'll know in which direction it will be. It's nice if the scale is good quality and accurate, and has a sliding marker to clearly show when you've reached the target pull weight.



    I pull slowly and evenly to 10lb, that's the weight I decided to start with, remove the spear from the vice and see if it bent. Then do it again increasing the pull weight by small increments until the shaft bends. It's a single clean bend so I can straighten the shaft after. That's it.



  • Very cool experiment Dan. Were you comparing different shaft diameters, or different types of steel?

    Promontorium Tremendum

  • 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.

  • I am doing something much the same these days - except, I wont really want to bend a spear. I do my testing with the spear placed horizontally and hang a set weight at a set distance (3kg @ 50cm) and measure the deflection.
    I shoot pneumatics so no carbon spears for me. Still, I'd like to find the stiffest stainless ones.


    So far, on my first go, I did notice that my 6.75mm Devoto spear was stiffer than the Pathos of the same thickness. Funny cuz Pathos has such a buzz going. But then again, Devoto is run by one older guy who probably doesn't give a hoot about buzzing his products. Not talking trash about the guns, though - I actually just bought one. Just saying the one Pathos shaft I have is not as stiff as at least one Devoto that I have;-). It wasn't that much. Something like deflecting 1 cm more, like 10cm instead of 9cm or something like that.


    Once I have more testing done, I'll share more findings, too.

    The post was edited 1 time, last by Diving gecko ().

  • What useful measurement/result will you get if you don't bring the shaft to the bending point? Deflection in itself is irrelevant because the ideal shaft is one that would flex endlessly without acquiring a permanent bend.

  • What useful measurement/result will you get if you don't bring the shaft to the bending point? Deflection in itself is irrelevant because the ideal shaft is one that would flex endlessly without acquiring a permanent bend.


    Easy tiger, it seems the two of us are not out to test the same:D


    I will, like I said, have a measurement of which of my spears are the stiffest, which may or may not be the same as being best at resisting bending.
    I haven't yet bent a spear, but then again, I don't shoot monsters where I hunt. What I want are the longest, most precise shots rather than a spear that might bend a little later. I think initial stiffness helps in the precision and speed department. Stiff should means less whip and thus more power transfer to the spear.
    E.g. perhaps the Pathos resists bends better than other spears (I have no idea), but one guy whose testing I trust found the Pathos spear to shoot less accurately when powered up than another brand - he speculated/felt/thought that it was because it whipped too easily since it is less stiff.

  • Call me crazy but is the strongest the best? I've had all types bend, but the stainless are the hardest to straighten back out. The spring steel bend back easier. And Black Grouper will bend any shaft made....at least on this planet. :D


  • E.g. perhaps the Pathos resists bends better than other spears (I have no idea), but one guy whose testing I trust found the Pathos spear to shoot less accurately when powered up than another brand - he speculated/felt/thought that it was because it whipped too easily since it is less stiff.


    Wouldn't an enclosed, or semi enclosed track cure that issue?

  • Possibly, but the same guy who made these comments used to swear by enclosed tracks and now wont touch them. He tests more vigorously and systematic than anyone I have ever heard of and has tested ETs vs. non-ET and says ET robs the shaft of too much speed. So, yeah, it might keep it more stable but you loose more than you gain (according to him).


    I think he used to post here? Not sure. But I'm sure a lot of you who visit the big bad forum and surf for tests once in a while have come across him. Lots of good stuff:
    https://www.youtube.com/user/majdq8/videos

  • Interesting. But if an ET slows the shaft, it's because the shaft is whipping and creating more friction? So if you used the same bands and shaft on a non ET gun, the shaft would be whipping too much and losing accuracy?


    I think powering any gun up too much loses accuracy if through nothing else, recoil.


    But getting back to bent shafts. I've had Black grouper bend 5/16 stainless also. LIke a pretzel. Thus I have many curtain rods made of bent shafts. The shafts aren't just bent, they're twisted a bit too. Really hard to straighten.

  • While I stated that I'm not specifically testing for hardness (which would be done with a Rockwell test) for our purposes hardness and bend resistance are closely enough related to make my test valid for hardness also. A shaft that performs well in my test will inherently be stiff enough as a speargun projectile.


    An enclosed track to me is about ease of use and an aesthetically pleasing element of the spearguns design. It's not about allowing me to overpower a gun and controlling shaft whip. Speargun power (band load) is dictated by its mass.


    If the shaft does get slowed down by an ET it's not significant enough to trump the other benefits of an ET. I'm about feeling comfortable and unencumbered in the water, increasing my stalking skills and getting closer to the fish. Not stressing over adding 3ft to the speargun's range at the expense of ease of use. Same reason I'm not interested in the roller design. Which BTW is now apparently obsolete with the advent of reverse rollers :rolleyes1:

  • A lot of good stuff here.


    Dan, are you willing to share your findings? Have you found any one manufacturer to be more resistant to bend? I'm curious your draw to 7mm also. Is it the fish and area you are diving? For me I am starting to venture away from the 7mm for the very reason of bent shafts. 7mm seems to bend to easily for me so I'm making a switch to a bigger shaft.


    DivingGecko, I have come to learn that no matter how much people praise Pathos, their shafts just don't do it for me for several reasons. For a long stretch they were all I would buy no matter my disappointment. They are priced higher locally than many other shafts. For me I thought, higher price, must be better. I believe the shafts are too prone to bend. They are not too stiff and so I speculate that their flight is not as true. So for me Pathos loses on stiffness, accuracy, and price. Now to continue the hunt for the perfect shaft.

  • Regarding the enclosed track... I am of the feeling that it does rob velocity. I don't know if there is too much debate over that. However, I do agree with Dan to an extent. Trying to push a shaft a few extra feet versus the benefit must be factored. Enclosed tracks have a time and place, and the fact they rob velocity does not mean they should be ruled out.


    One more thing to add regarding accuracy. To say mass dictates, I feel is a misstatement. Spearguns are unlike a firearm and the fact we are in the water just throws in a few more variables to account for. If anything dictates it is the combination of all that goes into the construction and rigging of a speargun down to the shooting line.

    The post was edited 1 time, last by Silentstoning ().

  • Yeah, I think the days of categorically saying only heavy guns can be powered up are behind us. I have seen enough videos to prove that to me;-). Many heavy guns have neglected other ways to make their designs more efficient so while they are heavy, they might still not shoot better than a much lighter but better designed and rigged gun.


    But I shoot pneumatics, so what do I know;-).
    And I shoot those pneumatics mostly in places where fish are few and very skittish and not huge. Hence, I like the long, fast and precise shots;-)


    Interesting to hear about the Pathos. I was guilty of believing the hype, too. I mean, I trust that the guns are good, and I already rigged the one I just bought as a gift for a friend with small ID 14mm rubbers. I'll get another spear for it, too. Probably a Sigalsub or Devoto.
    That said, I actually know a local engineer here in China, who makes spears out of 17-4ph and heat treats them. I have a pneumatic shaft from him that I will test against my other 7mm spears and if it is stiffer than the stock Pathos, I might just order from him for the Pathos gun.
    What Pathos did get right is pushing the shark fins waaay back so I would do that on my custom order, too of course:-)

  • I haven't tested enough shafts to share results. I just whipped up this test last night, I felt a shaft from a particular manufacturer was too soft and needed to prove it without a Rockwell test.

    One more thing to add regarding accuracy. To say mass dictates, I feel is a misstatement.

    I said

    Quote

    Speargun power (band load) is dictated by its mass.

    By that I mean; how much you can power up a gun before it becomes erratic depends on it's mass. Any speargun worthy of consideration will have the grip as close as possible to the plane of travel of bands and shaft, this is the single most important factor IMO. Other design elements such as raising the bands, flatter horizontal profile for the stock, enclosed track/deep tack, and even minutia such as tapering the ends of the bands, are nice but all negligible towards that end. A roller speargun design probably controls recoil better than all those combined, but who wants to dive with that mess. If this wasn't the case then simple aluminum tube spearguns like Rob Allen would simply not work.


    To me design elements for a reef speargun make sense when they make the gun compact and easy to carry/maneuver in a loaded state, for example allowing the bands to stack nicely. Quick and easy/comfortable loading, for example a deep or enclosed track guiding the shaft into the mech, auto resetting line release and simple shooting line routing. Durable with less probability of any of the parts failing. And of course aesthetically pleasing. All that done there's a reasonable range and accuracy that I expect from the speargun; a 7mm (9/32") shaft powered by 2 x 16mm small ID bands with 120cm band stretch to be able to hit a 2lb fish at the end of one wrap of line. That's it.


    More band power would mean that I'm going after big fish, lets say 60lb and up, that are easier to hit towards the limit of the speargun's range because they present a larger target, and require deep penetration at that distance. This means a heavier shaft and more bands, and for a speargun to not lose accuracy in this situation it must have more mass. Unless I'm specifically targeting big fish I don't want lug around a big speargun. And that's not to say that if handled correctly a lighter gun can't take big fish.

  • I totally misquoted you Dan, and I apologize for that. However, there are many out there that are of the belief everything can be corrected by mass, and that just isn't the case. Mass is an important factor, but it goes hand in hand with all of the things you listed above, and some. I think the main thing is finding the point where all of those factors collide in a optimum setup while being appropriately tuned.


    As far as rollers go, I'm not sold on them. While they may help recoil there are so many things I have heard to turn me off to them. I will just wait for them to be perfected or the fad to die down. Those are the only two directions I see rollers going. Either the concept is good and just poorly executed or it is something we will realize does not work. Until then I will stick with my classic setup.


    If you continue with this test to where you have something to share specific to manufacturers and/or preferred metals I would love to hear about it.

  • Stiffness is defined as the slope of the stress-strain curve. It is not affected by strength (and therefore heat treatment) in any way. Any kind of strengthening (heat treatment, cold working, etc.) only move the plastic yield point of the material further up the stress-strain curve, they do not alter its slope.
    Hardness is related to strength in the sense that hardness can be thought of as localized strength. The harder the material, the stronger it is, and vice-versa.


    Cheers. Don

    ''Great mother ocean brought forth all life, it is my eternal home''
    Don Berry from Blue Water Hunters.
    Speardiver Gear

  • All this talk of hardness...and stiffness....I get enough shit about this from my wife...:laughing:


    So which is a better shaft? The first pic is a spring steel, (or so I was told). This shaft has been bent but as you can see, it's straight. Ugly, but straight. You need to oil these or they will corrode a bit.
    The other pic is what appears to be stainless steel, the work of a small black grouper bent it way worse. I've already bent it back some. I'm going to remove the flopper and try to continue straightening it....if I get time before I leave for Thailand tomorrow....but I don't think I can get it perfect.
    Point is, the ugly shafts cost about $37. The other ones are quite a bit more. $60? But even if they're the same price, the ugly ones are more cost effective because the hunting we do....or at least when I was in my 50s :laughing:...shafts get bent. My buddy Doc says, as he does an Arnold type flex pose, "those rock fish (black grouper) can just ...grrrrrr...flex and bend your shaft". So if we can bend them back, it helps. The SS ones....I have more curtain rods made of SS....:D


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    The post was edited 1 time, last by hank ().

  • Hank, what length shafts are you using for the reef? I've found that at 170cm my 9/32 shafts are a wet noodle when a big black is on the end of it. Maybe if it was shorter a fish wouldn't have as much leverage on it. Bent or not it's hard for them to hole up with a long shaft in them!

    Promontorium Tremendum

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