User-and-big-knives-performances.pdf

User and (big) knives performances.

Outdoors-Magazine.com

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User and (big) knives

performances.

James

- Gear reviews and tests - Edged tools -

Publication: Wednesday 18 October 2006

Description :

Considerations on the influence of the user on knife performance.

Attribution-Non-Commercial-Share Alike License

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User and (big) knives performances.

This article is an essay to understand what makes a knife cut, independantly of the material it

is made of.

A consideration on blades geometries

Blades of chopping knives enter roughfully into 3 types, the forward curved blades, kukri (khukuri), bolos, falcatas,

the straight blades, modern knives machetes, and the backward curved blades, some parangs, goloks, sabres,

katanas and other sabres...

Each geometry presents advantages for a number of styles and uses, from chopping to slicing.

Outlines

a): backward curve.

b): straight.

c): forward curve.

Backward curved

Backward curved blades are excellent choppers, because when used with a rotating draw cut, their cutting power on

soft material is simply impressive. That is the power of the fearsome sabre cut.

For slicing, they are useful, as the slight belly can be used with advantage, as the tip may simply protrude in the air,

but the general curve helps slicing, and general use, it can be used for hashing, or even as a sickle, though may be

not the easiest geometry for that.

Forward curved

Forward curved blades also make excellent choppers. They can be often used in a variety of cut types, from the draw

cut to the "inversed" draw cut. While knives presenting only a recurve can rather be called "sickles". Knives of this

type often present a belly and a recurve, as with the kukri and bolo, and therefore can do a multitude of tasks and be

used into harder material that simply a sickle.

For slicing, well, it depends what and the exact geometry, for sure a sickle may not be a be a kitchen knife, While a

kukri does a lot of things quite well, thanks to it's usable belly.

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User and (big) knives performances.

Straight

Purely straight edges well are in between the two. A purely straight edge without a belly may also see limited use, but

on a machete, by example, it does allow to be used as a chopper or a slicer in a variety of strokes.

A consideration on blades profiles

Blades profiles will indeed greatly influence the efficiency. Read more about profiles at : Sharpening experiences

Types of cut, non dynamical

Types of cuts

a): Pushing.

b): Slicing.

c): Rolling.

There are three basic types of cut.

• (a) Pushing, Push cutting, when the edge is pushed through the material. as is is the case for a razor, a chisel.

Generally adapted to softer material. Pushing requires extremely polished and smoothly profiled edges in order

to minimize adherence and maximize ease of penetration

• (b) Slicing, Slice cutting, when the edge is used in a sawing movement the material. Slicing requires coarse or

dented eges in order to maximize the sawing movement. Kitchen knives are often used this way. Cutting ropes

and tough fibrous materials requires slicing.

• (c) Rolling, rolling the edge over the material, giving a rotation to the edge. Rolling requires like pushing polished

edges, and thin profiles. An ulu, may be used this way, some round bladed leather knives too.

Indeed, other uses are possible like piercing, but this mainly requires an adequate tip.

The combination of any or all of these together will be called shearing. and makes cutting in general more efficient.

Chopping is the act of push cutting after having accelerated the blade before it encounters the material, using it's

inertia from it's mass and speed in order to obtain a deep cut. Speed and inertia add dynamics.

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User and (big) knives performances.

Chopping: cutting under dynamics

These movements are shown here with knifes, but they could be imagined using different sort of axes, sickles or

other dynamical cutting tools.

Chopping

The normal movement of chopping, here shown with a kukri.

a): blade dragged a lot behind hand, creating a shearing effect.

b): blade at flat impact, push cut.

c): blade forced forward creating a shearing effect.

Depending on how a blade is held, different effects can be observed. the position b) is the most standard one, and

results in the edge simply push-cutting. This is here demonstrated using a kukri geometry , but is possible with all

kind of blade types. The position a) creates a shearing cut, because the edge enters the material at an angle. the

infamous guillotine's blade, angled at 45 degrees is said to improve cutting by 40 percent on a variety of materials

(not to say heads). The c) position creates the same kind of effect, but is also more dangerous as it makes the

movement prone to glances and therefore changes of direction.

Rotating or rolling

Rotating

This shows impact rotation.

Two possible ways: in the direction of the green arrows (tip down) of in the direction of the blue arrow (tip up).

Rotating at impact will also create a moderate shearing effect. The rotation can happen in two directions, tip down

and hand up, or tip up and hand down. Rotating is best done when associated with a draw cut or inversed draw cut.

Draw cut or sabre cut

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User and (big) knives performances.

Draw cut

Here is shown using different blade geometries how a draw cut can be performed.

a): using a kukri.

b): using a straight knife.

c): using a golok.

The draw cut or saber cut is achieved by pulling the knife at impact. Another way is to drag the blade slightly behind

the hand with the arm in a rotational movement from the shoulder. This creates a strong shearing effect, as the edge

push cuts and slices in the same time. It is in the example shown with various blade types. Some blade types make it

instinctive, some more difficult.

It is a surprising thing, as one can cut 6" sapling for a day in 3 or 4 strokes and then suddenly master a draw cut that

flies though it at first stroke, the blade not even feeling it or being stopped.

Inversed draw cut or wrist snap

Inversed draw cut

Here is shown using different blade geometries an inversed draw cut.

a): using a straight knife.

b): using a kukri.

c): using a golok.

The inversed draw cut consist of pushing the blade away instead of pulling it down. most people describe it as a wrist

snap at the moment of impact or slightly before. Again, in this example it is shown using different geometries and

some blade types like the kukri are better than others at that.

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