To groove, or not?

[Junglejim308]

I've always heard that "blood" grooves made the knife stronger, as well as making it easyer to pull out of the enemy.

I'm just thinking about strenght. A flouted bull,rifle, barrel is supposed to be stronger than a plain bull.

What do ya'll say?

 

[Crayola]

I suspect that a groove allows a little more flex in the knife, so it is srtonger with respect to hard use that will make the blade bend and such. I'm not sure how much of a fuller one needs to maximixe its usefulness. And I suspect that too large a fuller will just weaken a blade. Something to play with though. The Fuller you did on your dagger is awesome Dennis! AWESOME!

 

[glockman99]

Hmmm...I'm no Albert Einstein when it comes to physics, but how can removing metal from a blade make it stronger?

 

[Joe Talmadge]

On a sword, a fuller makes a much bigger impact. On a knife, there is some lightening of the blade, and the resulting blade is also stiffer for its weight, but given the small amount of metal removed, the impact isn't that profound. Is it stronger absolutely with a fuller? Some people much more knowledgeable than me in physics say yes, some say no, I haven't tested firsthand so I remain neutral (read: clueless).

 

[Cliff Stamp]

glockman99 :

how can removing metal from a blade make it stronger?

There is the argument that the curvature istelf can add to the strength, however as I understand it (I never looked at it in detail) this is only a correction effect, it is not large enough to compensate for the loss of strength do to the much more significant decrease in cross section, which is usually at the thickest part of the blade.

A friend of mine who is a mechanical engineer also learned traditional knifemaking using a natural forge. His teacher promoted the idea of a fuller adding to the strength of the blade, in this case it was true (he tested it) because you were seeing the effect of simply doing more forging not the inherent nature of the fuller.

In this case, because of the nature of the heat treatment, a large percentage of the final properties of the steel come from the forging. In modern blades that go through a full heat treatment after being forged (annealed, quenched, tempered), this isn't the case. The same guy also tested stock removal fullers, they did nothing but weaken the blade.

In any case, it is not like it is impossible to test. Make three blades without the fuller and break them off. Note the force required and the angle. Make three blades with a fuller and repeat. Use a bigger sample if you want a more precise estimate of the difference induced.


-Cliff

 

[Fox Creek]

this is one of those things that require careful attention to wording. Stronger than what? The same blade with out the fuller? Why no, of course not. Removing metal can only weaken it. Stronger than a blade of EQUAL MASS without a fuller ? Then yes. Think of sheet metal,flimsy sheet metal. Now think of it corrugated., it gets stiff and rigid. Same mass, different form. Cutting part of the sheet metal away (removing metal for the fuller, resulting in less mass) wont make it stonger. changing its form can make it stronger than it might have been otherwise.

 

[Joe Talmadge]

That's an extremely sensible explanation, and also explains why Jim Hrisoulas sees fullered blades as stronger. If he starts out with two lumps of metal, say 1.5 pounds each ( or whatever), and forges one fullered sword and one unfullered sword from the same mass, then what you say applies exactly.

 

[toothed]

Good question, I've often wondered about this theory. Is the fuller supposed to give more strength laterally against side-to-side forces or vertically against up or down forces? Or both? For some reason, I keep trying to visualize similarities of a blade with a fuller with an I-beam (sort of like the corrugated sheet metal analogy--greater strength through design and not more material). Chris Reeve's Kathathu has a "groove" or "fuller" down the middle of the blade but they use a different term to describe the design. Looking forward to reponses from those knowledgeable on this topic.