Balancing a knife: How to

J

J. D. Martin

Joined
Dec 6, 2001
Messages
59
Does anyone know the step-by-step procedure for balancing a knife? The little calculations involving its dimensions (length, thickness, width); its weight; where to add or take away steel to improve the balance; how to check whether a (throwing) knife is well-balanced; is there more to know to answer 'will it fly well?'
---- JDM
 
Good question. I have been making mine by copying others and making them a little bigger or smaller.
 
Having done a bit of cutlery tossing, I don't think it matters much.

All knives spin when thrown, and they will spin around the center of gravity, wherever that might happen to lie. Generally, we notice that handle-thrown knives tend to be heavier towards the point, whereas blade-thrown designs the opposite.

Good aerodynamics and stability would be more important than balancing, I'd think.
 
centerbalanced is good because you can throw it from the handle and the blade.

I would therefore suggest that you first go for handle heavy and adjust the weight by drilling holes in the handle...

Ookami
 
David, MWerner, Ookami>>>


David---

Yours is the practical method. Trial and error, starting with a reasonable facsimile of a successful design. How cd smthg so obvs hv eludged me entirely? I am an idiot. YOU design the knives.
Thanks for your note.
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Mr. Werner:
Your note straight off tells me this subject is beyond me. There are elementary principles of physics I cant call to mind that govern the motion of a spinning knife thru air. My grasp of aerodynamics is, like, nonexistent, empty set, approximates that of an unusually perceptive weasel.

So, balancing, you "...dont think it matters much..." Of course I am stooopid, but to me that seems wildly counter-intuitive. Like saying, of the two exactly opposing (by 180 degrees) blades of a helicopter prop/rotor, that it 'doesnt matter much if blade A is 10 feet long and blade B is 12 feet long.'

So you are saying there is no particular advantage in having the center of gravity exactly at the middle of the knife's length? Like, the merit of balancing a throwing knife is a myth?

I wonder what Bobby Branton [bobby@brantonknives, I think;he is the moderator of his own BladeForums discussion] would say on this subject? His throwers are impeccable, he is a champion thrower, he is a throwing expert, period.

And then sentence #2 of para #2 is a mystery to me.

"Good aerodynamics and stability wd be more important thn balancing." Aerodynamics, stability, balancing: I dont think I understand the basic concepts, much less how they interact.
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Ookami,

You make an excellent point: isnt it true, centerbalancing will mean tt the knife can be thrown equally accurately by the point or by the handle?
He suggest 'go first for handle-heavy and then skeletonize the handle as required.' Seems right to me.

All three of you guys, thanks for making points I'd been oblivious to.
--- J. D. :cool: :p
 
I don't know of anyone who's done any extensive testing of the aerodynamic characteristics of throwing knives; seems to be mostly trial and error.

At the short distances most knives are thrown from, it probably doesn't come into play a great deal. I have noticed that when attempting to throw at longer ranges (40-50 feet) that some designs will start to "plane" rather badly, and start to rotate around the "wrong" axis. That is, instead of just going end over end, they start to rotate like an aircraft propeller. Not good.

Most "pro" throwing knives I've seen are little more than slabs of steel with a point on one end. (speaking simply of geometry here...not finish, decoration or workmanship)

As such, You'd have to wonder just how much the actual balance point could be adjusted one way or another, without resorting to extremely wide blade points (like the leaf-shaped design) or extremely skinny handles.

I don't claim to be any sort of expert on the subject, I'm at best a casual thrower since my teens.

Here's another bone to chew on: We can successfully throw highly "unbalanced" items like tomahawks and meat cleavers. No one would claim that these items are even close to balancing at the center, but both can be thrown well by simply adjusting the distance till they hit blade (or pointy corner of the blade, in the case of the cleaver) first.

Good point on the versatility of center-balancing; most handle-thrown designs tend to be point heavy, and vice-versa for blade-thrown.
 
I think what mwerner means is that if the balance is a little off center it doesn't matter much.

For instance some japanese shuriken (the straigth ones) are handle heavy and axes and the like are blade heavy.

nevertheless they are not entirely handle heavy or blade heavy they throw just fine. when they are completely blade heavy eg and axe with a balsa wood handle it would not spin but float in the air. very much like a stone on a string you try to throw like an axe. the handle kind of counterbalances the head.

however centerbalanced is more versatile and better suited for beginners.

Ookami
 
Ookami,

You lay out an intriguing (as ol' Einstein called them)
'thought-experiment:
"...[A]n axe with a balsa wood handle wd not spin but float in the air...."

I have another one for you (tho not nearly as good). I was nattering on about throwing knives in an e-mail to Don Rearic, an expert on self-defense subjects. He made a certain remark about the aerodynamics of thrown knives, I cant remember it, except a lightbulb went off in my head and I thot "YES!! Like a javelin?!" WHY, NECESSARILY, does a throwing knife have to SPIN? Why cant we dream up some, brainstorm a design, that would be chucked like a spear, hurled like a javelin (and there, in that high-level Olympic sport, we would find all the booksetc transmitting the expertise to this new discipline.) Guess we would have to make up something new, a ramp, whatever, for a holding spot near the middle---but many possibilites arise. MOST important,for this new type knife you toss like a dart, it is probly best if it has 'FLIGHTS.' Now, we know, from the innumerable designs of man-made flying objects, there are inestimably many different designs for the 'wings'/flights of a FLIGHTKNIFE. ARROWBLADE, BIGDART.

Oh. Esau, my only point was to imagine another, like your own example, of a design for a man-flung weapon that has interesting characteristics.
:cool: :p J. D
 
The quest for non-rotating throwing devices is quite interesting. On the "Thrower" website, they have an article on a (Korean-derived?) throwing technique for bo-shuriken (the long, skinny ones)that involves letting the thing "slide" off your extended hand. Supposedly, practitioners can achieve non-rotating flight of some fair distance, 20 feet or so. Supposedly takes lots of practice...

There are indeed "dart" type devices, both currently and historically.

Several ancient warrior groups used a "war-dart", essentially a very short javelin with some sort of tail or fletching. At least one current maker was producing something similar.

Then there's lawn darts....
 
M. Werner,

That's right!!! I'd since thought of that: 'lawn darts.' Perhaps some of these FlightKnifes/BigDarts, in the designer's eyes, call for sidelong 'wings' or fins that would generate spin---get the dart to rotate, not lengthwise, but in a 'horizontal' spin (= so that the dart's point and rear stay pointed center). Like a football in the hands of an expert passer does; it MAY be that the rotation damps down wobble, helps keep the thrown-object in its preset course. Keeps it from tumbling end-over-end, as the ordinary throwing knife does.

I wonder, given that the usual 'balancing' of a throwing knife is intended to keep its end-over-end tumbling regular and controlled----I wonder, if a BigDart-type throwing knife ISN"T tumbling
end-over-end---what role does 'balancing' play in its performance?
(that is, of course, 'balancing' the weight of the knife so that its center-of-gravity falls at the exact midpoint of the knive's length] Who knows? a FlightKnife may require a dynamically sound body, or fins to reduce 'wobble,' the rear fishtailing. . .
And---are the fins straight and flat, or are curved like, oh, the
arms of a swastika {terrible example, but you get the point, to scoop out air or cup it or who knows I. I certainly don't, I'm totally incompetent, I hvnt so much as hd Aerodynamics 1A or Structural Engineering 101. Still, it's interesting to speculate about.
--- J. D.
 
There's a different "no-rotation" knife on the market that can be seen here. As mentioned on the linked site, it was used to set the distance record, 59'6" hitting an 8" bull's-eye. Interestingly, it uses no fins and can somewhat function as a standard knife.
flyingk1.jpg
 
J Claude,


Incredible. I saved the whole thing to file. I wonder what the Accuflite one, that someone else mentioned, looks like? I'll google Accuflite.

I'll get one of these. Because they're not much money. Just for the heck of it, as a 'novelty' knife--like a front-opening auto or other things fated to go the way of the dodo.

No flights! It does not veer off course 'due to the gyroscopical effect of its spin around the longitudical axis.' So that tells me it does spin like a well-thrown football. Still, wouldn't flights( even flights curved inward?) be one alternative method for keeping the missile on course? Don't all the U.S.'s missiles and rockets have flights? Titan, cruise, Tomahawk, etc.? Anytime it's an elongated projectile. Oxford American
Dictionary > gyroscope: "a device consisting of a heavy wheel which, when spinning fast, keeps the direction of its axis unchanged."

The knife-dart grip:'...index finger rest on the blade base surface. . . thumb and middle finger on [grooves?] in the handle [sides?]...' Almost as if your arm was a sling.

Handle (a) hollow and (b)made of Zytel. There's what allows it to be balanced.

What an intriguing little toy, J. Claude. Makes my prior empty speculation a waste of breath.

--- J. D.
 
Very interesting! of course, if you put enough spin on such a projectile, it'll be stable. (ie- rifle bullets)
 
while i am far from a professional (like Mr Branton) i have found that you can throw anything consistantly from moderat ranges with a little practice. i have thrown many different types of knives from professional's to kitchen knives to screwdrivers. what i have found is that shorter and lighter knives have a greater need for center ballence to be thrown accuratly. the larger the knife the lesser the need. knives that are handle heave throw better from the blade, and vise versa. center ballenced knives are more versatiel because it is easier to react to the changes in you targets range (1 spin, 1 1/2 spin etc.) I would imagin the idel self defense knife would be a smaller, dense and very sharp center ballenced knife designed for much closer range, of roughly 12 to 6 feet (meaning release point of your hand to the impact point of your target). i would imagine any other range would be unrealistic for combat or self defense effectiveness. i prefer to throw top heavy knives from the handle because they throw more like a tomahawk (whick i am much better at throwing) and i can control the knives spins better with this type of knife. i am young, only 19 and i'm sure many of you out their are much more knowledgable about the subject, just wanted to put in my two cent's, thanks
 
J.D. Martin,
I'm glad I could be helpful. Let us know what you think of the knife. I handled one at John Bailey's table at Blade, but I've never tried throwing one. Can't wait to see your results!
 
You can balance a knife to fly without rotation by putting weight on the back of the handle. I use tape to do so. I can easily stick knives from well past twenty feet, throwing with either hand, without their rotating at all. There is also a special grip (not the palm grip) that will allow you to throw in this style, which I call spear style, much more effectively. Practically everyone agrees that non-rotating throws are the only style that is useful for real self-defense. I have been perfecting this style for about twenty years now, and in fact I wrote a book about it, and am hoping to get an instructional video made someday.
 
Mr. Thorn,


It would be great to see an instructional video illustrating the "spear-style" of throwing. You describe weighting up the handle in order to balance the knife. I would have thought, given the typical dimensions of, say, a utility knife, that it is the blade that most often needs to be loaded up. I would have assumed that is why, where the ordinary utility knife has its 'tang,' instead, on a Tru-Bal or Pro-Flyte thrower, the tang is elongated and often has 'ears', viz. a (say, 1" long) wide spot on each side of the blade. I assumed this extra weight added onto the blade half of the knife was needed in order to move the center of gravity to the midpoint of the knife's length. That way it would tumble symmetrically, and not 'limp.'
But your technique achieves knifethrowing without rotation.
Terrific. It would be great to hear more about how this works.

--- J. D.
 
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