Fuller'vit

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...


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 ***

Nathans response is what you need to understand.
 
If you want to greatly stiffen a blade, do the reverse of a fuller. Upset the spine to be wider than the bevels (sort of a "T") and the blade will be very resistant to a bend in any direction. This is the way bayonets were shaped for a long time.
 
An old bayonet in my collection

fuller_zps5333580f.jpg~original


Many, if not most, had fullers and their function was to create a stiff stout blade that wouldn't fold without weighing a ton.

A blade of identical length and width and weight would be thin and flimsy.
 
OK..here is the bottom line,fullers look cool, all that science stuff just makes my head hurt;):)
 
Nathans response is what you need to understand.
I understand it, completely. I think you are mistaken and just haven't realized, yet.

Did my interpretation of your post sound right to you? Go to my last post and let me know.
 
Whew... Okay ... this confirms that you misspoke in the reply I am talking about. You unknowingly left out width (or thickness. take your pick)... do you realize that, now?

Weight and length just aren't enough to go by, whether you are talking about lateral stiffness or edge to spine rigidity.

Sorry for pushing the issue. I was just wondering if I was missing something. It's all good in da hood, now.
 
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An old bayonet in my collection

Many, if not most, had fullers and their function was to create a stiff stout blade that wouldn't fold without weighing a ton.

A blade of identical length and width and weight would be thin and flimsy.

Yes. Like I said earlier, 2 dimensions and weight need to be identical for the comparison, not a single dimension and weight, which would as Rick said, allow one to be thinner with a fuller which of course would not be stiffer in the lateral direction than the thicker, unfullered blade. I think you're mostly right that we all are comprehending this and speaking past each other a little bit, or, in my case being a little pedantic about assuming someone means 2 dimensions when they only say one. I'm not trying to be pedantic about it for the sake of argument, only because it's important to understanding and communicating clearly what a fuller does, how it does it, and why it can be as you said earlier, an advantageous design feature.

Here is a bowie blade I modeled (and made if it matters), by dimension:
qYzyctQ.jpg


Constrained at the tang with the constant force I used for all simulations applied it deflects 1.994" at the tip.
UldiT7d.jpg


Constrained at the tang with the force applied to the edge it deflects .101" at the tip.
1PYCg0X.jpg


Now, cut a healthy fuller into that blade, which coincidentally reduced the mass exactly 1 oz by luck or poor simulation tolerance, it of course deflects more:
MloxCeI.jpg


Only slightly more in the edge direction.
v8pc1uY.jpg


So at this point - I think most of us agree, removing material from a blade to create a fuller, by whatever means, without retaining that mass somewhere else in the blade (same weight) does not stiffen it. What I take issue with is when people get lazy and say, as Rick posted originally, "Now I'm putting a fuller in to stiffen it." No, it's stiffer now than it will be when you put the fuller in. You're putting a fuller in to reduce the weight while retaining as much strength and stiffness as possible.

Then I added an ounce of mass back into the blade. I retained the same thickness of the spine, and simply made it taller.
Oic6Op0.jpg


And applied the load again, in the same points relative to the shoulders and edge which stayed constant:
yVtmqDI.jpg


This is what I was questioning about last night. It still deflects more in this axis than the non-fullered blade. It matters where you add the mass that would normally reside in the fuller, for example by creating a "T" cross section that's thicker at the top of the T than the original spine thickness. But putting these fullers in still weakened this blade when the .200" cross section max thickness did not change.

Apply the force to the edge:
LlbMGMV.jpg


And you see that making the blade taller DID make it stiffer in that axis.

So my conclusion is this: If you're building a knife and you are working within weight and size constraints, fullers are an optimal way to make weight without getting too small. If you can reuse that mass in either the width of the blade or the thickness of the spine, you can create a knife of the same weight and length, that acts stiffer, but where you use that mass is important in how the blade is intended to be used. A bayonet I would want to increase the "T" width thickness of the spine to resist the type of back and forth action that might occur when stabbing and withdrawing a blade. A chopper I would want to make taller to resist flexion in the other axis.

I'm not an engineer. My models and simulations are likely not perfect. I'm doing this to the best of my limited ability because it's within my ability where destructive testing is not, it's easy to share the information and that's my only goal is to share the best information I have because it's an interesting topic. If someone with more knowledge in FEA simulations can tell me I'm doing something wrong I'd love to know what it is because I don't have any formal training. Because of this I've tried to keep everything constant in the simulations as I possibly could, so they would be like a dial test indicator, maybe not tell us exactly how far this blade will bend with a given force, but only indicate the difference changing the shape and mass of the blade might cause.
 
Thanks, Kuraki, for taking the time to run those simulations. It perfectly illustrates the implications of manipulating cross sections and shows fullers for what they essentially are... "thoughtfully executed weight reduction voids" ... Ha!
 
Awesome. Those simulations are very informative. I was saying if you took the weight that would go into the fuller and redistribute it evenly throughout the design of the knife.

So for example you take that 1oz out of the fuller and the knife grows everywhere to absorb that 1oz evenly. (So the blade would grow in height and width and thickness.)

I guess what I'm asking is I've always heard that if you take say 5lbs of steel and make a bar of it that is say 3 feet long it won't be as stiff as if you took that same 5lbs of steel and made a 3 foot long I-beam out of it. That's what I've heard from my friends who work in the construction fields.

Do the simulations agree with this? I would think they should if making the spine of the knife thicker increased ridgidity of the knife when force was applied to the side of the tip. Likewise making the spine taller improved ridgity when force was applied to the edge. So if the knife grew evenly in a way where the blade was both thickened and heightened then it should make the blade more stiff?
 
Awesome. Those simulations are very informative. I was saying if you took the weight that would go into the fuller and redistribute it evenly throughout the design of the knife.

So for example you take that 1oz out of the fuller and the knife grows everywhere to absorb that 1oz evenly. (So the blade would grow in height and width and thickness.)

Yes, I believe that will make the blade slightly stiffer in all directions, and if that's what you originally meant in your first post I apologize, I misinterpreted it.
 
That is correct, Lapedog. Cross sectional dimensions have to increase to positively increase stiffness. It doesn't take much, as Nathan pointed out with his "nonlinear" reference in a previous post.

So, if hammering in a fuller into the flats of blade makes the spine swell and flare out a bit, you'll increase stiffness. The same thing would happen if you mushroomed the spine from the top... essentially fullerinfg/upsetting the spine to make it flare out, increasing the cross section to a "T", which has already been stated.

Take the same blade and PRESS in a fuller so that the thickness is maintained and only the length and width are changed. the stiffness will increase, edge to spine only... with no advantageous weight loss to boot!
 
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I understand it, completely. I think you are mistaken and just haven't realized, yet.

Did my interpretation of your post sound right to you? Go to my last post and let me know.

Go take a nap Rick, you are far to cranky
 
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?


Nice post. There are lots of good reasons to introduce fullers into a blade design. I think one has to think about long blades like swords to really appreciate what a fuller can do. Where the blade material's weight is distributed has a drastic effect on the ease and speed of controlling the sword, which is also expected to be subjected to impacts way stronger than a knife blade. Fullers increase surface area, and can spread out stress points and dull resonances, which can make something long and boingy "feel" stiffer. (lol does that even make sense?) :D

Every car hood has a creases in it to help keep it from vibrating like a flat sheet would (stiffen it), the style points are secondary.
 
Great points, Mecha. I never considered vibration and a fuller's effect on that but it makes sense. I am a drummer and have re-hammered several cymbals to change the sound. Lathe grooves also effect how a cymbal vibrates... so why wouldn't a fuller do the same?... and to a larger degree.

Very cool discussion. Now I want to make more swords!
 
I remember a physics/engineering demonstration from 50 years ago. IIRC, it was a demo explaining what can happen to a long bridge if the engineering isn't done right.

The professor showed a 3 foot piece of thin steel bar ( about 1" by 1/16") and demonstrated how it bowed easily under its own weight.
Then he brought out one that was two of these strips welded together from end to end in a cross/X shape. He showed how it was many times stronger now by setting the ends on two chairs and stacking some books on the middle.
Then to show that the strength was only on the X and Y axis, he grabbed the ends in his hands and easily gave it a half twist along the Z axis.
 
Great points, Mecha. I never considered vibration and a fuller's effect on that but it makes sense. I am a drummer and have re-hammered several cymbals to change the sound. Lathe grooves also effect how a cymbal vibrates... so why wouldn't a fuller do the same?... and to a larger degree.

Very cool discussion. Now I want to make more swords!

Oh hellll ya. :D

Thanks Stacy, that's a good anecdote. All relativities aside, Would a sword blade with a big fuller take a twist more easily? I'd bet so.
 
Oh hellll ya. :D

Thanks Stacy, that's a good anecdote. All relativities aside, Would a sword blade with a big fuller take a twist more easily? I'd bet so.
Not if you construct little suspension cable apparatuses with mirrored stanchions located at the ricasso and tip... in tandem of course.

You're welcome.:thumbsup:
 
Not if you construct little suspension cable apparatuses with mirrored stanchions located at the ricasso and tip... in tandem of course.

You're welcome.:thumbsup:

Yes, YES. More swords!

ZkgFOcp.gif
 
Rick, don't get carried away ! While a tennis racket has a 'sweat spot ' a sword may have two or three !!
T cross sections ? Well our bridge here has five I beams .The web is 8' high, web welded to the flanges . .The bridge has sections , 40' long. They are put together to form a bridge about 200 yds long ! It curves both vertically and horizontally !
It's beautiful ! Now I'm getting carried away ! :D
 
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