Predetermined Breaking Point?

Jens Schuetz

Jens Schuetz

Joined
Jun 24, 2013
Messages
4,162
In engineering we often introduce a predetermined breaking point to either facilitate easier replacement or prevent catastrophic failure somewhere more vital.

Could that make sense in knives and swords as well?

Most swords I've seen break, break at the guard. Even if the blade breaks in the middle it's also often breaks at the guard too, resulting in 3 pieces.

A predetermined breaking point away from the guard would allow the blade to break there more easily and thus leave the rest of the sword intact. One will be left with something more useful to fight than just a handle. Also the broken off piece will fall down further away from the user and thus add a bit of safety.
If one pries and batons with a knife during our beloved "zombie apocalypse/ lost in wilderness" scenarios and it breaks in the upper third instead of near the guard one would still have something to cut with and be able to survive of the land or kill some more undead.

Of course it has to be explained properly, or the customer will think "it broke because of that stupid weak spot" instead of "it had to break because of too much force but yippy because of that predesigned breaking point I still have something left to work with"

Let me know if my idea makes sense and don't hold back if you think it's complete bs.

Thank you.
 
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In essence you're suggesting putting a fuse in the system so when you overload it you pop the fuse.

The only way I could see that being useful is that if it was also repairable by the user or the maker after the overload.
 
Danke, Danke42,
It's working like a fuse but would probably look more like a groove across the flats.
Fixing it afterwards would be great but I don't see how. The advantage would simply be to have enough blade left to keep fighting and surviving until you can make it home and replace it with another sword/knife.
 
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If the weak point is at the guard and you're creating a weaker point (fuse)....... I think I'd pass on the fuse and keep the blade as strong as possible.
 
Ken H> said:
If the weak point is at the guard and you're creating a weaker point (fuse)....... I think I'd pass on the fuse and keep the blade as strong as possible.
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Then you are left with nothing if it breaks.

Also weaker doesn't mean weak. Some might sacrifice 2 percent strength to be 90 percent sure not to lose the complete blade in a worst case scenario.
 
I haven't made many swords, but the only failure I ever saw with one of them was at the pommel, tang junction. Caused by vibration after hitting a very immovable object:eek:. If you are seeing many failures at the guard, then the construction technique needs to be looked at. I have personally never had any blade fail at the guard.........

Darcy
 
They have had that on small knife blades for a long time

http://www.ebay.com/itm/48-pcs-Cutt...916102?hash=item1a09398c46:g:~tIAAOSwbsBXomqE

All joking aside, they metallurgy and engineering applied to knives and swords is to give them hardness, geometry, and metal types to minimize breakage, but maximize cutting. It would be pointless to deliberately design a weak spot in the blade. Once broken, it is broken ... be it two places or one place. In the days of life and death sword fighting, many swords were deliberately soft to allow bending without breakage. The edge needed sharpening regularly, but that wasn't an issue.The Japanese spolved the problem with a soft core and a hard edge. In a severe flex, the edge could crack, but the sword would only bend and not break.
Edge quenching or clay coating the spine on a carbon steel fighter does the same thing.
 
Reminds me of when I worked in maintenance at a large steel producer: we had an engineer in the finishing division who incorporated his design of a shear pin into an existing mechanism that was notorious for breaking. The mechanism was essentially just a large "chisel" that extended, retracted, and pivoted on a large arm to peel the outer lap of a steel coil out, bend it at an angle, a help to facilitate feeding the head end of the coil into the bending rolls at entry. During the time I was there, the chisel broke several times, but almost NEVER at the shear pin. This led to various revisions in material that the pin was made out of, the depth and width of the shear groove, etc... I think over about 6 or 7 times the chisel assembly was broken (almost a new place every time) the shear pin only worked ONCE. :D

The engineer in question was very happy to hear that it finally worked, though I wonder if his latest shear pin design every worked the same way again. hahah

In regards to moving/designing a failure point into a knife or a sword, I'm not sure you're really gaining anything, other than a weaker knife or sword. Ok, my blade was just reduced by half, but where's the next weak spot after that?
If the tang/gaurd area is a weak spot to begin with, it's still going to be a weak spot after your designed "weaker" spot fails. Sure, there may not be as much force against it because your blade is only 1/2 or 1/3 as long, but then why not go the other way? In stead of making the blade half as strong, make the tang/gaurd area twice as strong.

Personally, I've never really gotten the whole "this knife NEEDS to be indestructible!" idea. If you need a pry bar, use a pry bar. Need a hammer, use a hammer. Need an hatchet or an ax, use a hatchet or an ax. I understand that things happen, and sometimes you have to use knives in ways they're not intended. I broke the tip off of my favorite folder prying some wire out of a fence when I locked my keys in my car in the middle of nowhere on a cold and rainy evening. Do I wish the tip was twice as thick so that it wouldn't have snapped off? Well, then it wouldn't have cut as well as it did for 99.9% of the other times that I was using it properly. Do I wish there was a shear line above where it broke so that less of the tip broke off? No.

Long story short, I see where you're coming from, but I don't really see it as useful or beneficial, all things considered.
 
DEllis said:
I haven't made many swords, but the only failure I ever saw with one of them was at the pommel, tang junction. Caused by vibration after hitting a very immovable object:eek:. If you are seeing many failures at the guard, then the construction technique needs to be looked at. I have personally never had any blade fail at the guard.........

Darcy
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Never seen one break at the pommel/tang but it makes sense. Worse than immovable is another blade moving with similar speed in the opposite direction against yours. :-O

What was interesting, once a blade got hit in the upper third and broke where it was impacted but at the same time it also broke around the guard. I'd almost call that shattering. That it happens often would be overstating a bit. Out of 350+ fights in training and tournaments it happened 4 times without too much power seeming to be the cause. Were those blades exceptions and hardened a bit less than ideal or does every blade get tired over time?
 
I don't see the advantage to creating a spot that will, in the end, INCREASE the chance of failure. If you hit something with a sword with enough force to break your sword, and you need to hit it again, you are screwed.
 
Stacy E. Apelt - Bladesmith said:
They have had that on small knife blades for a long time

http://www.ebay.com/itm/48-pcs-Cutt...916102?hash=item1a09398c46:g:~tIAAOSwbsBXomqE

All joking aside, they metallurgy and engineering applied to knives and swords is to give them hardness, geometry, and metal types to minimize breakage, but maximize cutting. It would be pointless to deliberately design a weak spot in the blade. Once broken, it is broken ... be it two places or one place. In the days of life and death sword fighting, many swords were deliberately soft to allow bending without breakage. The edge needed sharpening regularly, but that wasn't an issue.The Japanese spolved the problem with a soft core and a hard edge. In a severe flex, the edge could crack, but the sword would only bend and not break.
Edge quenching or clay coating the spine on a carbon steel fighter does the same thing.
Click to expand...
Thanks for weighing in too. What do you think of flexible instead of deformable? Was Japanese steel not be able to achieve this or would it have come with another set of problems?
 
knife to a gunfight said:
Reminds me of when I worked in maintenance at a large steel producer: we had an engineer in the finishing division who incorporated his design of a shear pin into an existing mechanism that was notorious for breaking. The mechanism was essentially just a large "chisel" that extended, retracted, and pivoted on a large arm to peel the outer lap of a steel coil out, bend it at an angle, a help to facilitate feeding the head end of the coil into the bending rolls at entry. During the time I was there, the chisel broke several times, but almost NEVER at the shear pin. This led to various revisions in material that the pin was made out of, the depth and width of the shear groove, etc... I think over about 6 or 7 times the chisel assembly was broken (almost a new place every time) the shear pin only worked ONCE. :D

The engineer in question was very happy to hear that it finally worked, though I wonder if his latest shear pin design every worked the same way again. hahah

In regards to moving/designing a failure point into a knife or a sword, I'm not sure you're really gaining anything, other than a weaker knife or sword. Ok, my blade was just reduced by half, but where's the next weak spot after that?
If the tang/gaurd area is a weak spot to begin with, it's still going to be a weak spot after your designed "weaker" spot fails. Sure, there may not be as much force against it because your blade is only 1/2 or 1/3 as long, but then why not go the other way? In stead of making the blade half as strong, make the tang/gaurd area twice as strong.

Personally, I've never really gotten the whole "this knife NEEDS to be indestructible!" idea. If you need a pry bar, use a pry bar. Need a hammer, use a hammer. Need an hatchet or an ax, use a hatchet or an ax. I understand that things happen, and sometimes you have to use knives in ways they're not intended. I broke the tip off of my favorite folder prying some wire out of a fence when I locked my keys in my car in the middle of nowhere on a cold and rainy evening. Do I wish the tip was twice as thick so that it wouldn't have snapped off? Well, then it wouldn't have cut as well as it did for 99.9% of the other times that I was using it properly. Do I wish there was a shear line above where it broke so that less of the tip broke off? No.

Long story short, I see where you're coming from, but I don't really see it as useful or beneficial, all things considered.
Click to expand...
Lol. Sounds like a typical engineer to me. I'd be happy too. :-D The idea is the same.

Swords don't break that often but if it does, one might prefer to have half of it left than none. That the left over half breaks again seems very unlikely.
Yes the hole sword a tiny bit weaker than without the predetermined breaking point but that doesn't mean it breaks instantly when you look at it the wrong way. It will still only break if excessive forces are applied or maybe the alloy wasn't as homogenous as it should have been or some guy made a mistake hardening it etc. There are many reasons why it could break and the very slightly weaker spot will ensure it breaks in a way less dooming to its user.
Anyways, that's the idea. Since the helpful experienced guys here dont see that as an advantage I guess it is none.

Thanks everybody.
 
Kevin McGovern said:
I don't see the advantage to creating a spot that will, in the end, INCREASE the chance of failure. If you hit something with a sword with enough force to break your sword, and you need to hit it again, you are screwed.
Click to expand...

The idea is to increase it, you are right. However only a tiny little bit. Thus if it breaks (not from simply blowing at it, mind you) it breaks in a way that you still have something sharp and pointy left to use.

I don't get why I'd be screwed if I need to hit something twice. Maybe the first time my sword got hit and the second time I hit back. Either way if the second hit happens with half a sword or an empty handle could make a big difference. :-D

Thanks for your opinion.
 
Jens Schuetz said:
The idea is to increase it, you are right. However only a tiny little bit. Thus if it breaks (not from simply blowing at it, mind you) it breaks in a way that you still have something sharp and pointy left to use.

I don't get why I'd be screwed if I need to hit something twice. Maybe the first time my sword got hit and the second time I hit back. Either way if the second hit happens with half a sword or an empty handle could make a big difference. :-D

Thanks for your opinion.
Click to expand...
Point is, unless a sword has a defect in it, say, like a weak point built into it, it shouldn't break. So if it's properly made, and some thing you are fighting breaks it, running would most likely be the preferred action.
 
Everybody.
I guess nobody disagrees that it would be preferable for a sword to break in half than to have the blade completely separate from its handle. Of course best would be no breakage at all, ever, but things happen.
The only question is how much overall integrity one wants to sacrifice 0% 2% 10% or if it's achievable by other means.
Making the guard area thicker seems reasonable but then wouldn't it break right above it where the blade thins to its normal thickness?
 
Kevin McGovern said:
Point is, unless a sword has a defect in it, say, like a weak point built into it, it shouldn't break. So if it's properly made, and some thing you are fighting breaks it, running would most likely be the preferred action.
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Thanks. I just wish all swords were made properly or at least have a guarantee that mine is unbreakable no matter what happens in a fight and no matter how old it gets.
 
Your predetermined breacking point topic has been taken care of by the distal taper geometry.
It is difficult to reinvent one wheel that has been running through the centuries ;)
 
stezann said:
Your predetermined breacking point topic has been taken care of by the distal taper geometry.
It is difficult to reinvent one wheel that has been running through the centuries ;)
Click to expand...
Excellent point.
Though the blades which broke were all distally tapered.
 
I agree that it would be better to address the cause of breakage and strengthen there in the initial design. Im not well versed in swords and sword breakage, but I do see a surprising amount of no just weak knife designs, but design's that could so easily be made 2x stronger with a bit of basic structural engineering.
 
If my knive break , I want to break at ricasso .... blade without handle is more usable then piece of blade with handle ............
 
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