Hardness of Hooks
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I was the originator of this hook design in the early 1970's when I was working for Ed Leeper. I took an aid fall when an original Chouinard narrow base hook rotated off the edge it was on as I watched. I sketched out the original wide base Leeper hook which we made in two versions, a wide one that was stronger and a narrow one that would fit in a quarter inch bolt hole for when aid bolts pulled out leaving only a hole, which was actually fairly common. We made the Leeper z pitons out of 4130 steel so that is what we used. We would work with soft annealed sheet and send the finished hooks and pins to Denver to be heat treated. The testing was done by weighting them to failure while hanging off an edge or in a hole. If the hardness was too high they would fail in a brittle fracture. If too soft the hooked tip would open up. In the end we used the same hardness as the pitons as that was convenient. The hardness was relevant and we empirically found the best hardness by testing to failure. I have no idea what anyone does now. That is where the Logan hook came from. |
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Mike Slavens wrote: Tensile strength (aka yield strength) is a material property. You can't translate into strength of a part without knowing the dimensions of the part and how its loaded."Tensile strength" is the breaking strength under tensile load, and is different from Yield Strength (load which causes permanent deformation, but not breaking). grog m aka Greg McKee wrote:Rockwell hardness has nothing to do with tensile strength.Harness correlates pretty well to UTS, at least for Steel: quora.com/What-is-the-relat… There's even an ISO standard on it: iso.org/iso/catalogue_detai… Are you thinking of Yield strength? |
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Jamie Logan wrote:I was the originator of this hook design in the early 1970's when I was working for Ed Leeper. I took an aid fall when an original Chouinard narrow base hook rotated off the edge it was on as I watched. I sketched out the original wide base Leeper hook which we made in two versions, a wide one that was stronger and a narrow one that would fit in a quarter inch bolt hole for when aid bolts pulled out leaving only a hole, which was actually fairly common. We made the Leeper z pitons out of 4130 steel so that is what we used. We would work with soft annealed sheet and send the finished hooks and pins to Denver to be heat treated. The testing was done by weighting them to failure while hanging off an edge or in a hole. If the hardness was too high they would fail in a brittle fracture. If too soft the hooked tip would open up. In the end we used the same hardness as the pitons as that was convenient. The hardness was relevant and we empirically found the best hardness by testing to failure. I have no idea what anyone does now. That is where the Logan hook came from.Dude! You are the Logan behind the Logan hook! Do you have any stories from that time period you could share? I am amazed at the stuff you guys were designing/manufacturing. |
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Jamie Logan wrote:I was the originator of this hook design in the early 1970's when I was working for Ed Leeper. I took an aid fall when an original Chouinard narrow base hook rotated off the edge it was on as I watched. I sketched out the original wide base Leeper hook which we made in two versions, a wide one that was stronger and a narrow one that would fit in a quarter inch bolt hole for when aid bolts pulled out leaving only a hole, which was actually fairly common. We made the Leeper z pitons out of 4130 steel so that is what we used. We would work with soft annealed sheet and send the finished hooks and pins to Denver to be heat treated. The testing was done by weighting them to failure while hanging off an edge or in a hole. If the hardness was too high they would fail in a brittle fracture. If too soft the hooked tip would open up. In the end we used the same hardness as the pitons as that was convenient. The hardness was relevant and we empirically found the best hardness by testing to failure. I have no idea what anyone does now. That is where the Logan hook came from.Thanks for posting Jamie! Loved many Leeper tools like cam hooks, Z's and of course, the Hooks. :) |
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I decided against testing in a steel block as the problems I´ve encountered using the Talon was in limestone (I use hooks for positioning while bolting) is that the edged of the flakes often burst out so wanted to know if this is the normal failure mode. And from the side:- Smallest hook failure 194kgf (1.90kN) Medium Hook failure 342kgf (3.35kN) Large Hook failure 404kg (3.96kN) All failed by bending open until the hook springs free from the hole. The higher the force the more the hooks are permanently distorted. Suprising was the miserable bit of cord didn´t fail at the hole in the hook! |
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Spectacular work Jim! Thank you for sharing! |