What's with the cut out blades on folders? | Thank you for...

Oct 25, 2018

48thRonin2Unless you're hammering on the spine or whacking the knife into things, i can't imagine it's going to just break on it's own. (neither of which should be done with a folder anyway, as I'm sure you already know) That example might be a little more angular than some, but all the corners on that one are radiused, none are sharp corners. In theory, it seems to me that the force applied to the knife would travel through the blade in a triangular pattern between the stop pin, the pivot, and the contact point on the edge, right? I think in more cases than not that energy would be traveling under the cutout, if that description makes any sense, not up and over through the spine. But I guess that depends on exactly where the stop pin is located. From a known designer and a respectable manufacturer though, I'm sure they've considered this. And I don't recall ever seeing anyone saying they broke a knife in the way you're talking about, have you? Is it weaker than the same exact tall blade without a cutout? Sure, in theory. But is it not the same (or maybe even a tiny bit stronger) as a knife with just a shorter overall blade height? Like, if you lopped off that whole top, would it still look to be of questionable strength to you? I have one of those Minithiriums being delivered in a few days, and will be sure to post pics of the tear down to show how much steel is left around the pivot, and the angle to the stop pin, to see if you still think it's a concern on that one

Oct 25, 2018

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48thRonin2

117

Oct 25, 2018

KavikThank you for your reply! On a previous drop, two users had their (solid) D2 blades snap between the pivot hole and the stop pin notch. The responses on this forum were the usual apologist bs, "well, out of a drop of 200+ knives, ONLY two broke, so the probability is..." blah, blah, blah. It seems to me that there are two types of purchasers in the world:

Those with a lot of money who fill a safe full of "safe queens", and,
Those who carry a knife and use it for whatever needs doing, and need to depend on it's reliability 100%. I am in the second group. As I said in a separate post, I use my knives (all of them) to slice, cut, and stick. I have no "safe queens".

What people who don't use their knives on a daily basis don't understand is that, when a blade fails, your personal probability just went to 100%. I have used the spine of a (closed) folder to knock out takedown slide stop pins on FUBAR'd polymer semiautomatic pistols. Ditto with the butt of the grip, which is why I find any knife with a pointy or "glass breaker" butt on the grip a useless selling "feature". That design flaw also negates the ability to "palm" the blade and push the entire knife, handle and all into an object for maximum penetration. We probably disagree, and that's O.K., but the majority of overpriced knives here on MassDrop are artistic expressions, not working tools. Handles with sharp angles, exposed liner edges may look impressive, but when you start using that knife for actual cutting of dense or resistant materials, you start losing skin from your hands and your personal effectiveness using that particular knife deteriorates rapidly. Just to let you know where I am coming from, my first job as a teenager was working in a slaughterhouse / meat packing plant. In those harder, less gentle days the way we killed hogs was by shackling their rear hooves and stringing them up by their rear hooves while still alive and kicking from a conveyor belt from the ceiling. My specific job was to first, stick the live hog in the throat and slice across the hog's throat. Particularly challenging if it was an older boar with tusks. My second task was to slice open the hog from anus to throat and pull out all of the intestines WITHOUT piercing the intestines and ruining the meat - while the hog was still moving and the conveyor belt was still moving. Pigskin is a very dense, tough hide to pierce, and my blades could not fail in mid-cut. I know that my experience is not the norm for those subscribed to the Blades Forum, but I still judge every blade by the same criteria - will it work or fail for what I need to do with it, and will the handle design injure my hand under hard use? What the knife looks like is of no importance to me. Just my $0.02.

Oct 25, 2018

Oct 25, 2018

48thRonin2This is weird, we seem to have posted at just about the same time, and my other post disappeared. Sorry if it shows up a a duplicate later, but i'll roll it up into this response I don't mind at all if we end up disagreeing, that's what makes conversations interesting lol And it's all guesswork and theories anyway, no right or wrong till anything is proven. But the point i was trying to get to is whether or not that's really as weak of a point as you think? I remember the ones you're talking about having broke, but in those cases it was too thin of a ring of steel left around the pivot pin, that had been further milled out for a bearing cutout....definitely not great, but not sure it relates to this scenario What I was trying to say is that I don't think much force from the edge would really even be transferred up and over that hole based on the geometry between the pivot pin and the stop pin. For example, with this knife i have on hand :

Any force on the edge of the blade will pull against the opposite point on the pivot pin while pushing against the closest point on the stop pin. So if you were cutting at the point indicated on the edge above, it would be pulling along the bottom line of the triangle and pushing along the top. The main stress line here is below the cutout. Moving further to the heel would move out further away from the cutout. I don't think you'd have much stress at all in the "arm" above the cutout until you brought that stress line above the centerline of the hole. But at that point you're well past the tip of the blade Admittedly, i don't do a ton of heavy heavy cutting with folding knives at this point in my life, I have other tools for any work that would break a folder. And if I DO need to put that much force and it has to be a knife, I've got fixed blades for that. I just think it might be a non issue unless the designers did a very poor job of laying out the rest of the pivot geometry....and i also think your more likely to have it fail at the lock or around the pivot pin (like those other two) long before you get enough pressure involved to snap above the cutout. Another point being that in order for that "arm" to break JUST from pressure on the edge of the blade, the entire blade below the hole would need to deform to allow the upper "arm" any room to move in the first place, wouldn't it? That's why I was originally saying you might be able to break it by whacking the spine, but probably not by using the blade Plus, finger flicking is more fun! Lol

Oct 25, 2018

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48thRonin2

117

Oct 25, 2018

KavikAgree with everything that you bring up, geometry, force vectors and how much blade material separates the cut out from the pivot hole and stop pin notch will determine whether or not it will become an issue. Another thing is whether or not the blade is cast (as in powdered steels) or drop forged with the cutout already formed or if the cutout is literally cut out of the blade - casting or drop forging being preferred before final tempering, physically removing material from bar stock with a plasma cutter or mechanical grinder / cutter can set up some issues for the final temper. (i.e., removing material that way may make the area around it more brittle if the blade gets too hot). Good to have an intelligent conversation on here. (I still comment on "mall ninjas" in the "tactical" blades discussion!)

Oct 25, 2018

Oct 26, 2018

48thRonin2Yeah, always enjoy a good, educational discussion 👍 I didn't get into steel types or manufacturing methods since we were talking about a general design feature, not a specific knife, but those are all excellent points as well. Along with steel type your also want to consider final heat treat, whether the steel is going to be super hard and brittle, or a little softer and more forgiving... Whether it will bend or crack, and result in just a ruined knife, or a catastrophic failure that potentially puts the user at risk of injury Side note : I wonder if a cut out from bar stock wouldn't be an issue if for with a water jet and before final temper? God, i want a CNC and a waterjet sooo bad lol

Oct 26, 2018

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48thRonin2

117

Oct 26, 2018

KavikHey, maybe if you're good, Santa will bring you a CNC machine and a water jet cutter, along with a lifetime of Hitachi tool steel bar stock... LOL! Make you an offer... you make them, ship them to me, and I'll "test" them...

Oct 26, 2018

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Oct 26, 2018

48thRonin2Lol i wish. First I need "Santa" to bring me a house, with a bit of land, so that i have room first to build a wood shop, then the machine shop would come after that...

Oct 26, 2018

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