Fuller'vit

Lapedog said:
Honestly I was just guessing I have no idea. But you have more experience it seems. So is what I said inaccurate? Taking 1 lbs of steel and forging it into a knife with a fuller so the resulting knife is 1lbs will not be stiffer than forging a knife where the result is 1lbs without a fuller?
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Maybe. It matters where the metal resides. It's not a question of mass alone, or dimensions alone, because the cross section and direction of the force matters.

It's why I brought up fluted barrels. Being cylinders and symmetrical it's easier to say definitively that a fluted barrel and unfluted barrel of the same weight and length, the fluted one will be stiffer because it's diameter and cross sectional area are necessarily larger than the unfluted one. There is only one place for the material that would have resided in the flutes to go, increasing the diameter. It doesn't matter which direction force is applied because they are symmetrical.

A knife generally isn't as symmetrical. I think it matters where that material resides and which direction the force is applied.

Maybe I'm wrong. I will model it and do another simulation on it tomorrow.
 
That would be awesome! Thank you for taking the time to do those simulations!
 
My (likely uninformed) understanding was a fuller was a way to remove weight without making the blade uniformly thinner overall. In made up numbers of oversimplification a given blade with a fuller could have an overall thickness at spine (or center if double edged) of 1/4" and weigh a certain amount. A blade of the exact same length and width without a fuller could only be 1/8" to hit the same weight. In comparing the stiffness of the two blades the one that is overall thicker but has a fuller should be stiffer. If that's an accurate understanding, it could be accurate to say a fuller let's you "make a stiffer blade" if you are meaning the stiffness you can hit at a given weight. It wouldn't be accurate though to say you can take a knife that is forged out and has a given stiffness and make it stiffer than it currently is by putting a fuller in it.
 
See you're pinning two dimensions, along with weight. In that case I think you are correct 100% of the time. But if you pin one dimension and weight, then the knife with a fuller may even be thinner than the one without, with a very wide blade.
 
I've got this neat sword bayonet . Most of the blade has a T cross section and a fuller !!! Toward the pointy end it's flat .The whole blade is a yataghan shape !! And put on the end of your musket it makes a nice pike. Put that in your computer !! :D
 
I think everyone understands there is a direct correlation between removing material and removing weight, it is a 1:1 ratio, obviously.

I think a lot of folks don't understand there is a non-linear correlation between thickness and stiffness. When you double the thickness of a beam it is twice the weight (duh) but 8 times stiffer. <--- A lot of folks aren't aware of that. Displacing the material in a spine (upsetting it) in a way that increases the thickness of that spine will make a stiffer blade for a given weight.

Historically speaking weapons like swords frequently included a fuller to increase their strength and stiffness for a given weight. This was true of weapons where cost was no object, it wasn't a matter of making due with the material at hand, it was simply good engineering.

There are plenty of modern designs where a fuller is simply reasonable engineering. For example there are weight distribution issues on a large chopper that could be addressed by making a blade a bolo shape or using a fuller.

There is a difference between a cosmetic fuller that is thin and shallow and a functional fuller that actually removes significant weight and allows a given design to have a thicker spine. I wouldn't broadly disregard the fuller as superfluous, it depends on the design and intent. I see it as a way of getting some of the durability of somewhat thicker blades while eliminating unnecessary weight. Who doesn't like reducing non-useful weight?
 
AVigil said:
It is not a matter of putting metal on a fullered knife, it is that a fullered blade that is the same length and the same weight will be stiffer then the unfullered blade of equal length and weight.


That is why they they put it their, it is not for looks.
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Are you saying that thickness and width can vary? as long as Length and Weight are identical? I think you've left too many variables open to come to that conclusion.
 
Karl B. Andersen said:
Fullers were originally a place to GET material from. If you forge that area inward, the displaced mass goes outward, making the blade wider. That's all it ever was.
In the distant past, they just couldn't order a wider piece of steel from Fastenal.
They had to learn to work with what they had.
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I don't agree with this. Perhaps at times it could come in handy but I believe fullers have a "higher" function than being thrifty with material.
 
Rick Marchand said:
Are you saying that thickness and width can vary? as long as Length and Weight are identical? I think you've left too many variables open to come to that conclusion.
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Read Nathans post, that should clear it up for you.
 
A steel tape measure like this wouldn't be as stiff and wouldn't hold it's own weight outstretched if not for the curve of the steel. This basically amounts to one really long thin blade where the whole blade essentially functions as a fuller does it not? This makes me think that a fuller must help in some way to stiffen a blade, but I don't know...

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I think the whole idea behind a fuller is to provide maximum rigidity and strength with minimal weight. I think a tape measure and an I-beam are good examples of that...but that's just my opinion. :D
 
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The tape is shaped that way to add stiffness, but that's not a fuller. It's making a curved surface out of a flat piece of steel.
The curved surface makes it so the bottom side of the curve concentrates the forces trying to bend it (gravity) on to a single "axis" (for lack of a better word) making it more ridged on that axis. It resists bending downward towards the bottom of the curve. Turn a tape over and it easily bends.

A fuller is a completely different animal.

An exaggerated fuller is an I-beam. Strong (for its weight) in one direction, vertically, but weak in the other, laterally.
 
A.McPherson said:
The tape is shaped that way to add stiffness, but that's not a fuller. It's making a curved surface out of a flat piece of steel.
The curved surface makes it so the bottom side of the curve concentrates the forces trying to bend it (gravity) on to a single "axis" (for lack of a better word) making it more ridged on that axis. It resists bending downward towards the bottom of the curve. Turn a tape over and it easily bends.

A fuller is a completely different animal.

An exaggerated fuller is an I-beam. Strong (for its weight) in one direction, vertically, but weak in the other, laterally.
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You are probably correct, but to me a fuller down the length of a sword would be kinda like having that curved steel of the tape on both sides. Put two curved steel tapes like that back to back they'd be even more stiff and it wouldn't just flop when you turned it over. I don't see how it is so different.
 
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R.C.Reichert said:
You are probably correct, but to me a fuller down the length of a sword would be kinda like having that curved steel of the tape on both sides. Put two curved steel tapes like that back to back they'd be even more stiff and it wouldn't just flop when you turned it over. I don't see how it is so different.
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The difference is that in the tape you get a cross section as thick as the depth of the "u" in change of the flat cross section thickness... increasing stiffness.
In a fullered sword the cross section remains the thickness of the blade, regardless you digging a fuller into it. The stiffness remains the same, just a bit less since you removed some material from the cross section.
But this is less noticeable, infact if you double the width of a stock you are not doubling its stiffness, but as Nathan explained, any adding to the cross section in the direction of the force applied, you increase stiffness by ^3.
This trade off makes for saving weight easily without sacrifying stiffness. And if you forge in the fuller and the displaced material is used to let the spine thichness GROW, then you have a stiffer blade, but you don't save weight.
It depends on the blade project...following function
 
The issue in making a comparison is that it is impossible to have a blade of equal size and weight. The extra metal has to go somewhere. It goes into a thicker blade or a lighter blade, thus they no longer are equal. A thicker blade will be stiffer.

The proper comparison is either "Of the same L/W/H dimensions (The fullered blade will be lighter), or "Of the same weight" ( The fullered blade will have different L/W/H)..

The argument can easily be explained by looking at an I-beam. You can't compare an I-beam with a solid bar of steel "of the same weight and size", because physics says they can't be both.
 
AVigil said:
Read Nathans post, that should clear it up for you.
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I read Nathans post... maybe I'm just interpreting yours improperly... or maybe you left out something. I still don't think it pans out with only the length and weight being the constants. and your conclusion implies that fullers make things more stiff... which they don't.

You said...
... it is that a fullered blade that is the same length and the same weight will be stiffer then the unfullered blade of equal length and weight.

That is why they they put it their, it is not for looks.
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Are you saying that a 1lb piece of steel .25 x 1.5 x 12 would be less stiff than a 1lb piece of steel .125 x 2 x 12 with a fuller in it?

*** those dimensions aren't the same exact weight. I just used friendly numbers for the example ***
 
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I don't think anyone thinks taking a knife and cutting a slot in it makes it stiffer do they? It's when it is incorporated into a design and is part of redistributing material to increase area moment of inertia that a fuller increases stiffness and strength. Reading all the posts here I think everyone gets that and some folks are just talking past each other?
Although the one guy who thinks an I-beam is stiff in one direction and flexible in the other direction (compared to a solid bar of the same weight) may be somewhat misunderstanding something, but I think everyone here basically agrees on the overall concept?
 
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