Grind
Encyclopedia
Clip point
thumb|250px|A [[Bowie knife]] clearly showing the clip pointThe clip point is one of the three most common knife blade shapes used . Clip point blades have the appearance of having the forward third of the blade "clipped" off...
or drop point
Drop point
Drop point is a knife blade that slopes on the spine of the blade from the handle of the knife to the tip of the blade. This allows the spine of the blade to continue forward to the tip of the blade....
knife
Knife
A knife is a cutting tool with an exposed cutting edge or blade, hand-held or otherwise, with or without a handle. Knives were used at least two-and-a-half million years ago, as evidenced by the Oldowan tools...
, sabre
Sabre
The sabre or saber is a kind of backsword that usually has a curved, single-edged blade and a rather large hand guard, covering the knuckles of the hand as well as the thumb and forefinger...
or cutlass
Cutlass
A cutlass is a short, broad sabre or slashing sword, with a straight or slightly curved blade sharpened on the cutting edge, and a hilt often featuring a solid cupped or basket shaped guard...
, axe
Axe
The axe, or ax, is an implement that has been used for millennia to shape, split and cut wood; to harvest timber; as a weapon; and as a ceremonial or heraldic symbol...
or chisel
Chisel
A chisel is a tool with a characteristically shaped cutting edge of blade on its end, for carving or cutting a hard material such as wood, stone, or metal. The handle and blade of some types of chisel are made of metal or wood with a sharp edge in it.In use, the chisel is forced into the material...
, etc.), though different tools and blades may have lent their name to a particular grind.
Grinding involves removing significant portions of metal from the blade and is thus distinct from honing
Honing (metalworking)
Honing is an abrasive machining process that produces a precision surface on a metal workpiece by scrubbing an abrasive stone against it along a controlled path...
and polishing
Polishing
Polishing is the process of creating a smooth and shiny surface by rubbing it or using a chemical action, leaving a surface with a significant specular reflection In some materials polishing is also able to reduce diffuse reflection to...
. It is notably done when first sharpening the blade or when a blade has been significantly damaged or abused (such as breaking a tip, chipping, or extensive corrosion) A well maintained blade will need less frequent grinding than one which is not treated well.
The terms edge angle and included angle can be important when talking about grinding. The edge angle is measured between the surface of an edge and a line running from the point of the cutting edge to the back edge. The included angle is the sum of the edge angles. All other things being equal, the smaller the included angle the sharper the blade and the easier it is to damage the edge.
An appropriate grind will depend upon what the blade is to be used for and the material from which the blade is made. Knife manufacturers may offer the same model of knife with different grinds on the blade and owners of a blade may choose to reshape it as a different grind to obtain different blade properties. A trade off exists between a blade's ability to take an edge and its ability to keep an edge. Various grinds are easier to maintain than others or can provide a better shape over the life of the blade as the blade is worn away by repeated sharpening. In material science terms, harder steels take sharper edges, but are more brittle and hence chip more easily, while softer steels are tougher
Toughness
In materials science and metallurgy, toughness is the ability of a material to absorb energy and plastically deform without fracturing; Material toughness is defined as the amount of energy per volume that a material can absorb before rupturing...
, and are used for knives such as cleavers
Cleaver (knife)
A cleaver is a large knife that varies in its shape but usually resembles a rectangular-bladed hatchet. It is used mostly for hacking through bones as a kitchen knife or butcher knife, and can also be used for crushing via its broad side, typically garlic....
which must be tough but do not require a sharp edge. In the range of hardnesses used for knives, the relationship between hardness and toughness is fairly complex and high hardness and high toughness are often possible at the same time.
As a rough guide, Western kitchen knives generally have a double-bevel (approximately 15° on the first bevel and 20–22° on the second), while East Asian kitchen knives are made of harder steel and are ground at 15–18°, being either wedge-shaped (double-ground) or chisel-shaped (single-ground).
Process
A sharp object works by concentrating forces which creates a high pressurePressure
Pressure is the force per unit area applied in a direction perpendicular to the surface of an object. Gauge pressure is the pressure relative to the local atmospheric or ambient pressure.- Definition :...
due to the very small area of the edge, but high pressures can nick a thin blade or even cause it to roll over into a rounded tube when it is used against hard materials. An irregular material or angled cut is also likely to apply much more torque
Torque
Torque, moment or moment of force , is the tendency of a force to rotate an object about an axis, fulcrum, or pivot. Just as a force is a push or a pull, a torque can be thought of as a twist....
to hollow-ground blades due to the "lip" formed on either side of the edge. More blade material can be included directly behind the cutting edge to reinforce it, but during sharpening some proportion of this material must be removed to reshape the edge, making the process more time-consuming. Also, any object being cut must be moved aside to make way for this wider blade section, and any force distributed to the grind surface reduces the pressure applied at the edge.
One way around this dilemma is to use the blade at an angle, which can make a blade's grind seem less steep, much as a switchback
Hairpin turn
A hairpin turn , named for its resemblance to a hairpin/bobby pin, is a bend in a road with a very acute inner angle, making it necessary for an oncoming vehicle to turn almost 180° to continue on the road. Such turns in ramps and trails may be called switchbacks in American English, by analogy...
makes a trail easier to climb. Using the edge in this way is made easier by introducing a curve in the blade, as seen in sabers, scimitar
Scimitar
A scimitar is a backsword or sabre with a curved blade, originating in Southwest Asia .The Arabic term saif translates to "sword" in general, but is normally taken to refer to the scimitar type of curved backsword in particular.The curved sword or "scimitar" was widespread throughout the Muslim...
s, and katana
Katana
A Japanese sword, or , is one of the traditional bladed weapons of Japan. There are several types of Japanese swords, according to size, field of application and method of manufacture.-Description:...
, among many others. Some old European swords (most memorably Hrunting
Hrunting
Hrunting was a sword given to Beowulf by Unferth in the ancient Old English epic poem Beowulf. Beowulf used it in battle against Grendel's Mother.Beowulf is described receiving the sword in lines 1455-1458:-Hrunting's failure:...
) and the Indonesia
Indonesia
Indonesia , officially the Republic of Indonesia , is a country in Southeast Asia and Oceania. Indonesia is an archipelago comprising approximately 13,000 islands. It has 33 provinces with over 238 million people, and is the world's fourth most populous country. Indonesia is a republic, with an...
n style of kris
Kris
The kris or keris is an asymmetrical dagger or sword nowadays most strongly associated with the culture of Indonesia, but also indigenous to Malaysia, Southern Thailand and Brunei. It is known as kalis in the southern Philippines. The kris is famous for its distinctive wavy blade , but many have...
have a wavelike shape, with much the same effect in drawing or thrusting cuts.
When speaking of Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
ese edged weapons, the term refers to the grind of the blade: an edge with more niku is more convex and/or steep and therefore tougher, though it seems less sharp. Katana
Katana
A Japanese sword, or , is one of the traditional bladed weapons of Japan. There are several types of Japanese swords, according to size, field of application and method of manufacture.-Description:...
tend to have much more niku than wakizashi
Wakizashi
The is one of the traditional Japanese swords worn by the samurai class in feudal Japan.-Description:...
.
If it is required to measure the angles of cutting edges, it is achieved by using a blade edge protractor ( or goniometer) see CATRA Hobbigoni
Typical grinds
- Hollow grind-a knife blade which has been ground to create a characteristic concave, beveled cutting edge along. This is characteristic of straight razorStraight razorA straight razor is a razor with a blade that can fold into its handle. They are also called open razors and cut-throat razors.Although straight razors were once the principal method of manual shaving, they have been largely overshadowed by the safety razor, incorporating a disposable blade...
s, used for shaving, and yields a very sharp but weak edge which requires stroppingRazor stropA razor strop is a flexible strip of leather or canvas used to straighten and polish the blade of a straight razor, a knife, or a woodworking tool like a chisel...
for maintenance. - Flat grind—The blade tapers all the way from the spine to the edge from both sides. A lot of metal is removed from the blade and is thus more difficult to grind, one factor that limits its commercial use. It sacrifices edge durability in favor of more sharpness. The Finnish puukkoPuukkoA puukko is a small traditional Finnish belt-knife with a single curving cutting edge and a flat back.- Design :The basic components of a puukko are a hilt and a blade along with a sheath, which can be attached to a belt. The blade is short, typically less than 100 mm.The flat back allows the...
is an example of a flat ground knife. A true, flat ground knife having only a single bevel is somewhat of a rarity. - Sabre grind—Similar to a flat grind blade except that the bevel starts at about the middle of the blade, not the spine. Also named "Scandinavian Grind", it produces a more lasting edge at the expense of some cutting ability and is typical of kitchen knives. Also sometimes referred to as a "V Grind", made with strength in mind and found on tactical and military knives.
- Chisel grind—As on a chiselChiselA chisel is a tool with a characteristically shaped cutting edge of blade on its end, for carving or cutting a hard material such as wood, stone, or metal. The handle and blade of some types of chisel are made of metal or wood with a sharp edge in it.In use, the chisel is forced into the material...
, only one side is ground (often at an edge angle of about 20 – 30°); the other remains flat. As many Japanese culinary knives tend to be chisel ground they are often sharper than a typical double bevelled Western culinary knife. (A chisel grind has only a single edge angle. If a sabre grind blade has the same edge angle as a chisel grind, it still has two edges and thus has twice the included angle.) Knives which are chisel ground come in left and right-handed varieties, depending upon which side is ground.- Japanese knives feature subtle variations on the chisel grind: firstly, the back side of the blade is often concave, to reduce drag and adhesion so the food separates more cleanly; this feature is known as urasuki. Secondly, the kanisaki deba, used for cutting crab and other shellfish, has the grind on the opposite side (left side angled for right-handed use), so that the meat is not cut when chopping the shell.
- Double bevel or compound bevel—A back bevel, similar to a sabre or flat grind, is put on the blade behind the edge bevel (the bevel which is the foremost cutting surface). This back bevel keeps the section of blade behind the edge thinner which improves cutting ability. Being less acute at the edge than a single bevel, sharpness is sacrificed for resilience: such a grind is much less prone to chipping or rolling than a single bevel blade. In practice, double bevels are common in a variety of edge angles and back bevel angles, and Western kitchen knives generally have a double bevel, with an edge angle of 20–22° (included angle of 40–44°).
- Convex grind—Rather than tapering with straight lines to the edge, the taper is curved, though in the opposite manner to a hollow grind. Such a shape keeps a lot of metal behind the edge making for a stronger edge while still allowing a good degree of sharpness. This grind can be used on axes and is sometimes called an axe grind. As the angle of the taper is constantly changing this type of grind requires some degree of skill to reproduce on a flat stone. Convex blades usually need to be made from thicker stock than other blades. This is also known as 'hamaguriba' in japanese kitchen knives, both single and double beveled. Hamaguriba means "clam shaped edge".
It is possible to combine grinds or produce other variations. For example, some blades may be flat ground for much of the blade but be convex ground towards the edge.