Blood grooves???

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Mar 14, 2000
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Please help me settle a debate. A friend of mine is CONVINCED that a fighting knife should have a blood groove. He says that it will allow a knife to be removed from it's victim more easily. Something to do with suction or vacuum and the blood groove allows air into the body cavity that it has been placed into. Don't worry, he's a Marine and he wants me to make him a "using knife" for his chosen profession. On the other side of the coin, I've read in several places that blood grooves are a bunch of hullabaloo. In my uneducated opinion, I think that they might have a tendency to weaken the blade. not to mention that if a person used a knife to defend himself, the adrenelin would more than make up for a lack of a blood groove when it's time to extricate the knife from it's victim.

What do you guys know about the subject?

Thanks,
Rick
 
That wasnt the purpoe of fullers. They were to lighten weight, if youre a tricky guy you can use them to add flexibility OR ridgidity. They have nothing to do with blood or such.
Actually as far as knives go, once you stab someone the blood on the grip added to all of the victims local muscles contracting can make removing it a b1tch.
So you are the correct one.
Joe Renner
 
To be honest I don't know. When I went through boot camp and infrantry training latter, I was told the fuller on the K-Bar was a blood groove to asist in removal from an unfriendly like your friend said. I still think that if the blade is stuck just wiggle it around a little, it'll come out.:)

However I beleive that a blood groove or fuller is to lighten a blade, and it can hang up on material being cut. A better way to me is to have a distally tappered blade that has nothing to hang up.

If done right a fuller shouldnt weaken a blade that much, but I don't realy see that it serves a purpass.

One note, unless he's maybe Force Recon or somthing, and even then, the primary use of the knife will be utility and field craft, not fighting, though that's always a posibility.
 
i it is called a fuller. one it lightens the knife/sword. two it can work like a steel I beam by ditribuding stress from impact and tourking. all the is no proof that muscles contract on a stab wound making it harder to remove. i don't know how this rumors got started but they are not based on facts.
 
Hullabaloo is correct. At least in the sense you are debating. Joe hits the nail on the head again, of course. :cool:

The blood thing. So, aside from completely undeniable pure logic, my EMT buddy could easily tell you the blood is gonna want go everywhere and guts are just gonna try to leave the body. All over the "blood groove". The "suction" thing is also bogus.

Lastly, you are dealing with a marine here. :rolleyes: But I guess if I was a marine going through boot camp, I wouldn't argue with the drill instructor on what does and does not work.


My .02.
 
Hey, here is what I remember from college. It was a while ago so it will be short and simple. Rhhino was pretty close. I don't know if a steel I beam distributes the stress, but the I beam is good because of its shape. The I shape increases the beams "moment of inertia (I)." A beams strength is dependent on its shape and the Youngs Modulus (Strength of material (E)).

By adding the fuller to the blade you are increasing the I of the knife and since the bending strength of the knife is directly proportional to its moment of inertia, its strength goes up. It is the same reason that a hollow tube is stornger than a solid bar of the same weight.

Anyway, that is what I remember, if i had spent more time studing the books and less time looking at the bottom of my beer glass, I could have some formulas for ya.:)

Oh yeah, I forgot to mention that by adding a fuller, you can lighten the blade. Keeping "strength" as a constant, the blade with a fuller will be lighter than a blade without one.
 
Thanks for the replies guys! All very interesting.

Laredo7mm, If I understand you correctly... If I make two identical knives (size, shape and weight) and I add a fuller to one of the blades, it will become stronger than it's counterpart? Or would the fuller just make it lighter and add strength so it's actually only as strong as it's counterpart? Would a fuller make the blade stronger in say a prying action as well as a chopping action? Just trying to understand as best I can.

Right now, I'm a firm believer in distal tapers and a proper heat treatment for strength and flexability (not to mention edge retention), I just need to convince my friend of it.

Thanks,
Rick
 
If you made two identical knives, and then forged the fuller into one blade, that blade would be stronger (in chopping) than the other knife. Right? I think so:) I think the main purpose of the fullers was to make blades lighter while retaining their strength, so the smith would forge in a fuller and use less steel.

When I think of a fuller, I think mainly of swords, not knives. I am no means an expert on either, but I think the advantage of fullering really comes into light on large blades. The fuller would strengthen the blade for chopping actions and not prying actions.

The fuller increases the moment of intertia along the neutral axis when loaded with the chopping action, which increases the "strength". Just off the top of my head, I would think the fuller would actually weaken the blade when loading it in a prying situation.

It would kinda be like laying a 2 x 8 x 12 across two saw horses. Lay it down with the big flat side parallel to the ground, and take a seat in the middle. If you are a big fat A$$ like me, the board will flex and maybe break. Now turn the board 90 deg so the big flat is perpendicular to the ground. Again take a seat, the board will not flex, so now me and all my fat friends have a place to sit.:)

That is why tou see the I-beam type floor joists being used in home construction now days. They have the same strength as a 2 x 8 but are made from alot less material. The "I" beam shape has two big parts (the top and bottom flats) that are far away from the center of the beam. The moment of inertia for the beam is the sum of the moments of its indiviual pieces. So the two big flats, and the vertical part all have their own moments. Each components moment is dependent on the distance it is away from the neutral axis. The neutral axis is perpendicular to the direction of the load. So the I beam has two neutral axii depending on how you load it. One moment of inertial is bigger than the other, so the beam is stronger when loaded perp to that axis. By putting the fuller into the knife blade, you are effectively moving mass farther away from the neutral axis, making that moment bigger, and the other moment(prying) smaller.

OK, I think I am confused now, but that is not hard to do. Usually happens when I try to think. I should just sick with studying the bottom of the beer bottle.:D

If you all have a machinist handbook, look up moment of inertia or bending moment, they have a bunch of info on how to calculate the stuff.
 
Laredo7mm, Thanks again for the info. It makes good sense to me. I was thinking that a fuller might weaken a blade in a prying type action, but I only had my gut telling me so.

So I guess that the trick now is to convince/sell my friend on a fuller-less blade. He's now had about 6 years of the marine corps drilled into his head. This one is going to be tough. I guess I'll have to send him a knife to compare against his trusty K-bar to see which is better. I'd better hurry up with my forging learning curve:eek:

Thanks,
Rick
 
A fullered blade will not be stronger in chopping motions, will be weaker in flexing motions. It will be lighter, sure. but if you cut anything you will have a lot of "drag".
The "I" theory applies only for weight management, the idea is its lighter than a solid bar and still has decent strength, its not strongER but plenty strong enough. An I is stronger than a flat of the same weight.

Joe Renner
 
Rick, aside from the blood groove being unnecessary and difficult to accomplish, why not just make your buddy's knife the way he wants it? Even if the concept is bogus for a knife, and I fall into that crowd also, it sure looks cool and probably won't hurt anything. I doubt even a hard core marine will be putting too much prying action on his custom knife. :D And that's what you're making, a custom knife.

As long as you are compensated for your effort, I don't see the harm in giving him what he wants. I'm working on a knife now that I think is foolish and looks silly, but I gave my customer a preview of the rough ground blade and he sure looked happy. That might be more key than being right! Just my 2c.

Interesting thread, thanks for all the great info. Naturally I had always heard that bit of folklore too and always questioned it.

Dave
 
Hi Dave, To answer your question, you would have to know this guy to fully understand my situation. He's like a 12 year old in a 30 year old body. He knows that I am going to be testing for my ABS Jouneyman stamp and all that it takes to accomplish it. I would not put it past him to fully test his blade when he receives it. On the other hand, I am relatively new to knifemaking and I want to keep my reputation as high as I can. My friend will be a great marketing tool for me if his knife performs. I understand where you are comming from when you pose your question, but I don't want to make my friend a tool that will potentially fail him when it's most needed.

Joe, Thanks for your input as well. My gut was telling me exactly what you are saying. The "drag" part of what you said makes sense for two reasons. There will be hips and valleys to catch on things and by creating a convex surface the surface area is increased which creates more potential for drag. I want to make my friend a knife that can stand up to just about anything that a Marine in a combat situation might come up against. Trust me, if this guy gets a chance to volunteer for combat duty he will be there. I want my knife to be a part of the reason why he comes back in one piece if you know what I mean.

Thanks,
Rick
 
if a knife can cut/stab its way into something, shouldnt it also be able to cut/"unstab" its way out?
 
Kenster.. I know exactly what you mean... Maybe the human torso is like one of those Chinese finger traps when it comes to knives;) It seems to me that in a situation that would require a knife to be used to dispatch an unfriendly, your adreneline would be so high that if the knife got stuck it would only be because the handle came off while trying to pull it out:D

Mike, Thanks for the link. That's a pretty handy looking contraption. It's giving me ideas for something else.

Rick
 
im fairly certain (from my years of engineering classes) that you cannot make an object stronger by removing metal. you can give it a higher strength to weight ratio, but an I beam isnt stronger than a solid beam of same dimensions. it does however save a LOT of material and weight.

its kinda like fluted barrels on a rifle, they dont make it stronger, but sure as hell make it lighter.

but i'll check on that, just to make sure im not talkin outta my ass.
 
a forged in fuller like they do on old swords should stiffen the blade and make it lighter. modulus of elasticity and all such as that.

an Engineer could probably tell you the real reason :)

any how a flat bar is esier to bend than one with a groove in it.

I read somwhere that the only time a (fighting type guy) had his knife hang up was when he got the blade in a joint.

Indian and Persian swords often had multi fullers in them.

I saw a neat little rig for doing fullers in blades one time, kinda like the gullotine tool with an adjustable edge guide for the back of the blade to rest on, probably much faster than lininig it up by hand.

just as this shape ][ is stronger in steel than this shape /

Look at a lot of different parts on machines and you will see what I mean. the fullers are there to increase stiffness, parts on lawnmowers for example.

I dunno that I'd want to bend test a completed blade with a fuller.

Might be interesting to try though.

for what it's worth my .02
 
You can also precisely scrape a fuller into a blade. I believe it's on Don Fogg's site.
 
There is no suction or muscle contraction to worry about when stabbing. However, the blade can become lodged in bones, like between ribs. This has happened to me on several occasions.

Though I'm sure you are busily planning every detail of the knife, which is good, I agree that there are far more important things you can focus on. For instance, if adding a blood groove were to make a defense/offense knife twice as good, (just for the sake of discussion) then by comparison, every 3 or 4 inches of blade length you add will make it 100 times better! How much have you used knives that were at least 20" long? (excluding crappy machettes) It's only been a couple years for me, but it's instantly obvious there is no comparison! If he wants a more powerful and versatile knife, take whatever blade length he's specified and double it! Though, this does require far more skill and know-how on your part, to keep it from getting too heavy, weak, etc.

Also, fullers may theoretically make the blade less aerodynamic, but that depends on how wide and deep they are, and how and where they're positioned on the blade. Also, their effect on aerodynamics will only be about 1/100th as important as the edge geometry and good grinds. (as I'm sure you know)
 
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