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Test to Destruction


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A while back, and since I really have lost my sense of when a thing happened (or so my friends tell me), I can only say within the last few months, I suggested that a TTD was needed, in response to a thread about stick versus full tang construction.

 

I took a knife that was on the bench that clearly was never going to get finished. It had been part of a group of ABS JS test blades that I didn't need. Forged 1080, differential HT (edge quench) 3, 4 hour temper cycles, rolled spine. When I pulled this out of the unfinished pile and looked it over, I decided that the tang was much beefier than I would generally put on a knife that size, so I ground it down, and squared the shoulders up as much as I usually do.

 

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These are the dimensions of the tang.

 

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The test handle is a piece of square tube with a couple of 5/16th bolts to hold things in place. I put a piece of micarta in to help pinch the tang.

 

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I made a couple of quick vids, which show my process, but it's the result that is interesting. I drove the blade down into the end grain of a power pole 3 times. The tang, which was dead soft, started to deform and then tore, starting at the bottom. It might have torn at a spot where I pinched the blade before I put the micarta spacer in the handle.

 

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You see what might be an area of hard material right in the center of the tang.

 

So what have I learned from this experiment?

 

1) It IS possible to break a tang on a knife, but it takes a lot of force. This one took 3 hard overhand blows before it failed, and even then, if didn't fail at the shoulders, but back in the soft area of the tang.

 

2) I don't think I'm going to change the way I make my every day sort of knife, but I may beef up the tangs on more hard duty pieces.

 

I do think that the handle on most blades would give up before the tang ever got this much stress on it. When I have a couple of minutes, I'll post the vids on my Youtube channel.

 

Thanks,

 

Geoff

Edited by Geoff Keyes
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Thanks Geoff ;

I have often wondered but never had a blade to spare. This test gives me some things to think about in my own construction, but at least I know I'm on the right track!!!

 

Kip

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Interesting !!

 

Jeoff, how was your quench achieved was it a vertical plunge or horizontal and did you do a draw back! I hope that doesn't sound dumb but, I am trying to figure if the blades quench played into that result!

 

Basically from what I am seeing and reading what you wrote it appears to have done as planned. I seriously doubt with a normal handle you ever would have been able to generate the force you used to break the tang! I must say you got me thinking though!!!!33.gif

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I love a good beefy hidden tang... I make them as wide as possible. The extra strength may never be needed, but if it is ever needed, its there.

 

I had one or two bend on me when I left them unquenched, so I've started giving them a differential quench. The verdict is still out on whether this is really viable, but they don't bend as easily...

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I use an edge quench, so the answer none of the above. I have a large flat pan with a stop plate in the pan. After I get the depth set, then I just run the edge into the oil and down onto the plate. I rock the blade if it looks like the tip isn't getting into the oil, and wait for the spine to go black, then quench the whole thing off. The tang should be dead soft, which this test seemed to show, it tore rather than fractured. The last several mono steel test blades, of which this was one, bent nicely into a curve. The handles were canvas micarta and they didn't bend at the tang at all. As I said, I took a lot out of this one before I tested it, because I wanted to test blades the way I mostly make them, not the way I made them for the test.

 

I've not had good luck with torch drawing the spine of a blade, and with the edge quench, you don't need to be since the spine never gets hard. A fellow maker, Rick Lucas, made a test blade and he full quenched it, then took the blade and buried the edge in wet sand. He used a OA torch and drew the spine to silver blue, nearly to dark red, about 10 times. We tried for nearly 30 minutes to break that blade, bending 90 one way, back to straight and 90 the other way without ever breaking it. We finally gave up and went for beers.

 

Geoff

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Interesting test Geoff, I've always quenched the same way, but drop the whole blade in after about 6 seconds, so the handle firms up a bit...except on daggers obviously...never had a problem! Learned from Goddards 'the wonders of knife making' and only had one serverely abused blade eventualy fail, so I'll stick with it!

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I always thought that well made stick or hidden tangs had an un-deserved bad rap.

Afterall, it's a design that has worked fine for swords for how many centuries?

Like anything else it's how it's done that is important, kept wide as reasonably possible and with blades that have good heat treatment, as well as good handle materials, the hidden tangs can run right along with full tang knives except when it gets into out and out abuse.

Making knives for three decades now both ways, never had any issues reported with hidden tang knives, and most of my customers have been users. In the end, at least to me, most other arguments are moot.

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Geoff, I gotta say though, that is an exceptionally small tang of the stick variety even, was this primarily for test purposes?

I would not expect that you would make knives on a usual basis with such a teeny tang.

 

Cool vid and test

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No, I would normally go a somewhat bigger. The tang that it had was way overkill, since it was supposed to be a test knife and I didn't want any surprises. OTOH, the tang on my MS test knife (not the last one, I'm afraid, since my window expired) was not much larger than that one, though it was at least semi hard. What I wanted to test was whether a stick could hold up to severe use, and if the square shoulder transition was an important failure point.

 

I was a bit disappointed that it ripped, but that might be operator error, OTOH, I was pleased that the shoulder was not the failure. I'm thinking about a second test. A similar knife with a micarta handle, clamped in a top and bottom test handle, and see where that takes us.

 

Geoff

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Interesting video and thanks for the extra info!!!!!

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Generally I try to keep the hidden tangs 1/2 the width of the blade nominal, and usually closer to 3/4 mostly, and taper it some to the butt end, but as little as possible. With good handle materials I found the knife as strong overall as slabs on tapered or drilled full tangs.

I do like to ht the tang halfway or so along with the rest of the blade.

Especially using maples and birches I think they are just as strong on all practical levels as a full tang construction.

Imo, of course.

 

Good work Geoff. This stuff is where the rubber meets the road.

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OK, I chosen my next vict....ahem...test knife. It's a 7 inch clip point that I can make again in a heart beat. Differential HT and a stick tang. It's mostly ground, so I can do a 100 grit grind to an edge and call that good. My plan is to make a micarta handle with a bolster (no guard, which will just get in my way) and no pin (since I hardly do pinned handles any more). I was then going to take two u-bolts and attach that to a length of schedule 40 black pipe. Then I'm gonna beat on my wood target until something breaks.

 

If there are other tests folks would like to see, let me know. This is not a test of the edge, per say, but a test of the tang/ricasso junction, and the strength of my usual construction method.

 

Geoff

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