"Blood groove" on 119/120

TAH

TAH

Joined
Jul 3, 2001
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I know blood grooves (fullers) have been discussed, but I could find anything specific to Buck. I believe the real purpose of the groove is to lighten and stiffen the blade, but I have a few questions...

1) Why does the 119 and 120 have a blood groove, but the 124 does not?
2) Does the shallow groove really lighten the blade enough to make a difference?
3) Are the grooves forged/stamped somehow or just ground/milled into place?
4) If just ground/milled, how would this stiffen the blade?
 
TAH,

My answer for Question 2 is that the groove does not lighten the blade enough to make a difference until you have a blade the size of a large sword. However, it does help to sell knives.

Bert
 
They don't actually stiffen or strengthen the blade, they just allow you to remove steel without as much loss of strength or rigidity as you would have if you removed an equivalent amount from the stock thickness.

So a knife using .25" stock with no fuller would be strongest and heaviest, but a knife with .25" stock and a deep fuller might be just as light as a knife with .2" stock with no fuller, but will be stronger and more rigid.

On smaller knives I doubt they provide much weight reduction and I think they become more of an aesthetic choice.
 
bdmicarta said:
Tell the writer to go get his degree in structural engineering and then rewrite his article. I already have my degree in structural engineering.
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Congrats on your degree. Curious, which part of the article do you feel is not accurate?
 
Insipid Moniker said:
They don't actually stiffen or strengthen the blade, they just allow you to remove steel without as much loss of strength or rigidity as you would have if you removed an equivalent amount from the stock thickness.

So a knife using .25" stock with no fuller would be strongest and heaviest, but a knife with .25" stock and a deep fuller might be just as light as a knife with .2" stock with no fuller, but will be stronger and more rigid.

On smaller knives I doubt they provide much weight reduction and I think they become more of an aesthetic choice.
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Yes, it might make is a bit lighter on a larger knife like the 120. Marble's made this popular with their Ideal, if I recall correctly. This led to the Ka-Bar knife design and on it goes. The Marble's version was much, much wider.
 
TAH said:
Congrats on your degree. Curious, which part of the article do you feel is not accurate?
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I'll dive in to the structural stuff. I am on the side of bdmicarta, in that I disagree slightly with the article.

The fuller, or blood groove does make the blade look like an I-beam. Why is an I-beam good? Picture an I-beam that is one-inch square across both the major dimensions. Now picture a solid bar 1 inch wide by 1 inch tall in cross section. The solid bar is stiffer, but the I-beam is nearly as stiff and a lot lighter. I-beams save weight and metal by putting a lot of metal where it is most useful to strengthen the beam.

So a long sword with a long fuller is light yet strong - but where is it strong? In a downward slashing blow the cross section of the blade looks like a tall thin I. The fuller has lightened the blade while keeping metal at the top thick and also the metal between the groove and the edge is thick. The I is working.

Thrust that same blade into something and bend it sideways - now the thin dimension is resisting the force and the "I" shape is not working.

So if blades crack or bend because of the shock load at the end of a downward, edge-first slash then the fuller has made the blade lighter while retaining strength.

If a blade cracks or bends because of a sideways bending force the fuller has actually weakened it slightly.

Do any of you (or the Field and Stream author) know of any Buck 119 or KABAR knives that failed in a downward edge-first slash? It ain't how I use mine.

So I think the groove is decorative, or based on folklore. Sometimes folklore is true, engineers do not know it all. But I cannot see a structural reason to add the groove.
 
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I'm having a hard time relating an I-beam to the little groove on the 119 blade. :D But I understand your point. :thumbup:
 
TAH said:
Curious, which part of the article do you feel is not accurate?
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"2: You stiffen the blade."

This part is untrue.

Take ANY blade, ANY shape, ANY length, it doesn't matter. REMOVE material from that blade anywhere along its length, it doesn't matter where or how as long as you don't reshape what is left. You REDUCE the stiffness of the blade.

If you take the material that you removed and put it back on the blade elsewhere, that is a different story. That's not what we are talking about. Removing material from one spot and adding back on in another spot CAN certainly strengthen and/or stiffen a blade.
 
bdmicarta said:
"2: You stiffen the blade."

This part is untrue.

Take ANY blade, ANY shape, ANY length, it doesn't matter. REMOVE material from that blade anywhere along its length, it doesn't matter where or how as long as you don't reshape what is left. You REDUCE the stiffness of the blade.

If you take the material that you removed and put it back on the blade elsewhere, that is a different story. That's not what we are talking about. Removing material from one spot and adding back on in another spot CAN certainly strengthen and/or stiffen a blade.
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I agree - it should say that by adding a groove you can stiffen the blade at a constant weight. But you still can only stiffen it in the vertical direction, not in the weaker, sideways, direction.
 
I always questioned the "stiffening" part, but wasn't sure if forging the groove into the blade might make a difference. Apparently not. Thanks!
 
Pondoro2310 said:
not in the weaker, sideways, direction.
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If you took the metal that was in the fuller and put it on the faces of the blade to make the blade thicker, you would stiffen it in the lateral direction. It's all about how much metal is located where. Take metal out and stiffness goes down. Take metal out and put it back somewhere else you might increase the stiffness.

I've had people tell me different things about forging. Most recently I've read that forging does not strengthen the metal. But we are talking about stiffness and forging doesn't change that at all. Alloying may change stiffness a small amount but for the most part steel is steel when you are talking about stiffness (Youngs Modulus of elasticity). (I know that the people that build firearms do, and I think the people that build racing engines also do, have a different opinion of forged parts vs. machined parts.)
 
The I – beam or Universal beam has the most efficient cross sectional profile as most of its material is located away from the neutral axis providing a high second moment of area, which in turn [for a given amount of material] increases the stiffness, hence resistance to bending and deflection."

The fuller also removes material from the neutral axis and, for a given amount of material, leaves more material in the areas subject to compression and tension if force is applied along the long dimension of the cross-section of the blade. So we get stiffer blades for a given amount of material or lighter blades of a given stiffness for resisting force along the long axis of the cross section (Think of a blade being used to strike down against a target.)

As the knives being discussed are not chopping tools, the practical need for fullers seems doubtful

BUT

Webster Marble put a wide fuller just behind the primary bevel in the "Ideal" becasue he thought it reduced friction when cutting thick meat. Either most makers didn't "get it" or didn't think it was true. From Marble's point-of-view, their fullers were and are decorative.
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