serration

File:Ortie.jpg, Urtica dioica]]

In nature, serration is commonly seen in the cutting edge on the teeth of some species, usually sharks. However, it also appears on non-cutting surfaces, for example, in botany where a toothed leaf margin or other plant part, such as the edge of a carnation petal, is described as being serrated. A serrated leaf edge may reduce the force of wind and other natural elements.{{cite book|first1=Alan R. |last1=Hemsley|first2=Imogen |last2=Poole|title=The Evolution of Plant Physiology |year=2005|page=220}} Probably{{clarify|date=June 2023}} the largest serrations on Earth occur on the skylines of mountains (the Spanish word sierra, as in the Sierra Nevada, means a saw). These occur due to the uneven action of landform edges pushing rock upwards, and the uneven action of erosion.{{cn|date=June 2023}}

Human uses of serration have copied, and gone beyond, those found in nature. For example, the teeth on a saw or other serrated blade serve a similar cutting or scraping purpose as the serration of an animal tooth. Tailors use pinking shears to cut cloth with a serrated edge, which, somewhat counterintuitively, reduces fraying by reducing the average length of a thread that may be pulled from the edge.{{cite book|first=Heather |last=Audin|title=Making Victorian Costumes for Women|year= 2015|chapter=2}} A type of serration is also found in airframe shapes used in certain stealth aircraft, which use the jaggedness of the serrated edge to deflect radar signals from seams and edges where a straight, non-serrated edge would reflect radar signals to the source. Screw threads show serration in profile, although they are usually shown in abbreviated or symbolic fashion on mechanical drawings to save time and ink. Brogue shoes are made with serrated edges on the leather pieces, for no known purpose at all other than style. The step clamp and step block assembly in metalworking adopt serration for the purpose of applying clamping pressure from an adjustable position.

File:Meyerco bolt action.jpg, and featuring a partially serrated blade.]]

Humans have used serrated blades since the Mesolithic era, when prehistoric humans made these from flint.{{Cite web|url=https://cotswoldarchaeology.co.uk/museum/microdenticulte/|title=Flint Serrated Tool|first=Cotswold|last=Archaeology|date=March 8, 2024}} A serrated blade has a toothlike rather than a plain edge, and is used on saws and on some knives and scissors. It is also known as a dentated, sawtooth, or toothed blade. Many such blades are scalloped,{{cite web |url=https://www.williams-sonoma.com/shopping/scalloped-bread-knife/ |title=Williams Sonoma |access-date=13 January 2023}} having edges cut with curved notches, common on wood saws and bread knives.

With kitchen knives, the finer serrated edge is found typically on paring and cheese knives, particularly for slicing harder cheeses like cheddar or Wensleydale. The wider scalloped-edge serrations are found on practically all bread knives and typically on fruit knives. These serrated knives are better able to cut through a firmer or tougher outer crust or skin without crushing the softer and more delicate inner crumb or flesh.

Serrations give the blade's cutting edge less contact area than a smooth blade, which increases the applied pressure at each point of contact, and the points of contact are at a sharper angle to the material being cut. This causes a cutting action that involves many small splits in the surface of the material being cut, which cumulatively serve to cut the material along the line of the blade.{{cite book|title=Desert Survival Skills |first= David |last=Alloway |publisher= University of Texas Press|year= 2000|page=38|ISBN =978-0-292-70492-3}}

Cuts made with a serrated blade are typically less smooth and precise than cuts made with a smooth blade. Serrated edges can be difficult to sharpen using a whetstone or rotary sharpener intended for straight edges but can be sharpened with ceramic or diamond coated rods. Further, they tend to stay sharper longer than similar straight edges. A serrated blade has a faster cut, but a plain edge has a cleaner cut. Some prefer a serrated blade on a pocket knife{{cite book|last=Hertzmann|first =Peter|title=Knife Skills Illustrated: A User's Manual |page=17|publisher =W. W. Norton & Company|year= 2007|ISBN = 978-0-393-06178-9 }} or on an emergency rescue knife, especially with the latter for its increased ability to cut through cords, ropes, and safety belts.

• Tooth serration — Vertical serration along edge of blade
• Single edge serration — Serration on one side, the other remains flat
• Double edge serration — Serration on both sides
• Fan serration — Side-to-side serration without necessarily having a toothed edge
• Micro-serration — Serration much smaller than thickness of blade creating something like a fan pattern

• Sharpness (cutting)

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{{wiktionary|serrate|serrated|serration}}

• [https://eaiainfo.org/2020/05/14/the-serrated-bread-knife/ "The Serrated Bread Knife," Chronicle of Early American Industries, 2010] - article documenting the production of American serrated knives and saw-cut knives back as far as 1838.

Category:Cutting tools

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