What is so great about tapered tang?

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then the question is, do you heat treat custom knives for bonehead users, or maximize strength?
 
It depends.... do your customers wear hockey masks and leather gloves?

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Wow, Thanks for the input everyone! It would be interesting to take some measurements on identical blades with tapered and untapered tangs to see which one held up to more force before a catastphic failure.

Peat
 
LB, thanks for chiming in on the whole fuller stiffness / strength to weight issue. Nicely explained. You don't see much discussion of moment of inertia or sectional modulus as it pertains to knife design. How refreshing geeky.

There are a couple things I'd like to add.

One, martensite is less dense than pearlite (so it takes up more space) so the edge (and spine) of a differentially hardened blade is under compression, reducing crack propagation in a manner similar to shot peening a weld. A surface under compression is frequently tougher. I'm not sure how much of a difference it makes in practice, but it works for me in theory.

Unhardened steel transmits shock energy differently than hardened steel, which may be relevant in a chopper (it certainly is in an anvil or hammer)

Almost 20 years ago I was a bicycle mechanic. I was surprised to learn that butted wheel spokes were (in practice) tougher than straight gauge spokes, not just lighter. The likely reason being, the thread on one end, and the bend on the other, were the weak points. Gradually thinning the spoke in the center (rendering it more flexible in tension) reduced the shock on the weak points and probably also allowed adjoining spokes to contribute more in an impact. The wheel wasn't stiffer, but it appeared to tolerate a larger wack without breaking a spoke. Makes me think a tapered tang might be harder to break in use. Also makes me think a tapered tang would be more likely to pop a scale loose (due to being more flexible)
 
Lucky Bob said:
Speaking as a mechanical engineering student, removing material from a solid object (filleting outside corners are an exception, but that's nitpicking) will never strengthen said object. What it will do is increase its specific strength, ie strength per weight.

When you flex an object, the parts that are subject to the most stress and therefore require the most strength are the ones being compressed or stretched the most, which are the parts farthest from the plane that is neither stretched nor compressed, usually the outside. That's why an I-beam has a higher specific strength when you apply a load along the vertical of the I, but not when it's perpendicular to that. When it's along the vertical, you have full width of material at the inside and outside of the curve, but when you do it the other way you have just the corners trying to resist a ton of stress. In knifemaking terms, that means that fullers lighten the blade but actually weaken it, just insignificantly against loads applied in the spine-edge direction.

Also, along the same lines, I'm pretty sure that, ignoring any lightening holes and resulting stress concentrators, a tapered bar will be weaker than an untapered one, just because there's less material to spread the load.

Unfortunately I don't have the relevant textbook handy to cite, but if you all would like, I'll see if any of my friends/classmates have a copy I can borrow.
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Yep, reviving an old thread.

The amount of stress you can put on a tang is proportionate to the amount of grip you can put on it.

if you are gripping the handle fully, you will be stressing the full width of the tang at the thickest and strongest part, if you are only gripping the last inch of the handle, the stress will be little and therefore will not affect the thinned tang any more than the full grip on the thick part of the tang.
 
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cotdt said:
... but you end up using more handle material. Handle material can be expensive.
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Handle material is purchased in blocks, whether you make tapered tangs or straight tangs, you purchase the same block.

Add the higher value for tapered tang = higher valued knife.
 
Lucky Bob said:
Yes, a soft blade might take a 90 degree bend without breaking, but the same force applied to a hardened blade will just make it flex without any permanent deformation, let alone failure.

As for the ABS, I second Cashen's take (which you seem to, as well) that the test is not so much that these are the properties that every knife should have as much as can you jump through the hoops we set.



Fair enough!


And Tinker, no need to quote you, I just wanted to say "right on!" :p
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I have to call BS on most of this. Look up modulus of elasticity. How much a hardened blade or mild steel will bend and flex back without taking permanent bend is dependent on it's thickness, not anything else. Period. You can have a sheet of 72 HRC 0.005 thick that you can wrap around a 1/8" rod but you will not do that with 60 HRC 1/4" thick blade.

You cannot apply all of those properties to any single blade but you can fudge the ABS test. Make a blade out of 1095, thick and heavy in the front 5" for the chopping, nice and thin in the back 5" for flexing, temper the spine for good flex; BAM!

of course I exaggerate, the differences required to achieve the required properties in a winning blade are so subtle and wouldn't be noticed by most knife enthusiasts.
 
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Edro20 said:
I thought that a tapered tang meant that as a knifemaker you had passed a test. That being the shower of sparks that burns your hands and arms while you grind it.:D
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I thought it was a sign of a hand forged knife.
 
69_knives said:
I have to call BS on most of this. Look up modulus of elasticity. How much a hardened blade or mild steel will bend and flex back without taking permanent bend is dependent on it's thickness, not anything else. Period. You can have a sheet of 72 HRC 0.005 thick that you can wrap around a 1/8" rod but you will not do that with 60 HRC 1/4" thick blade.

You cannot apply all of those properties to any single blade but you can fudge the ABS test. Make a blade out of 1095, thick and heavy in the front 5" for the chopping, nice and thin in the back 5" for flexing, temper the spine for good flex; BAM!

of course I exaggerate, the differences required to achieve the required properties in a winning blade are so subtle and wouldn't be noticed by most knife enthusiasts.
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We're beating an old dead horse here, but this was not BS. Lucky Bob understands that the stiffness of a flat steel object is a function of it's thickness. The flex mod is a constant regardless of hardness, everybody understands that. But what you're saying here is incorrect :

69_knives said:
How much a hardened blade or mild steel will bend and flex back without taking permanent bend is dependent on it's thickness, not anything else. Period. .
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Bend and flex back without taking a permanent bend is also a function of yield strength which is very much a function of hardness. Look plastic deformation vs elastic.


...in before the lock...
 
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