A pencil sharpener (also referred to in Ireland as a parer or topper) is a device for sharpening a pencil's writing point by shaving away its worn surface. Pencil sharpeners may be operated manually or by an electric motor. It is common for many sharpeners to have a casing around them, which can be removed for emptying the pencil shavings debris into a trash bin.
==History== Before the development of dedicated pencil sharpeners, a pencil was sharpened by whittling it with a knife. Pencil sharpeners made this task much easier and gave a more uniform result. Some specialized types of pencils, such as carpenter's pencils, are still usually sharpened with a knife, due to their flat shape. However, since the 2000s, a fixed-blade device with a rotatable collar has become available.
French mathematician Bernard Lassimonne applied for the first patent (French patent #2444) on pencil sharpeners in 1828, but it was not until 1847 that the pencil sharpener in its recognizable modern form was invented by fellow Frenchman Thierry Des Estivaux. The first American pencil sharpener was patented by Walter K. Foster of Bangor, Maine in 1855.John Lee Love was an African-American inventor of Fall River, Massachusetts, who created a portable pencil sharpener. The design was simple, including a hand crank and a compartment to capture the pencil shavings.The sharpener was patented in 1897 and has no evidence that it was ever produced Electric pencil sharpeners for offices have been made since at least 1917.
=== Prism sharpeners ===
So-called "prism" sharpeners, also called "manual" or "pocket" sharpeners in the United States, have no separate moving parts and are typically the smallest and cheapest commonly used pencil sharpener on the market. The simplest common variety is a small rectangular prism or block, only about 1 × 5/8 × 7/16 inch (2.5 × 1.7 × 1.1 cm) in size. The block-shaped sharpener consists of a combined point-shaping cone that is aligned to the cylindrical pencil alignment guide hole, into which the pencil is inserted. A sharp blade is mounted so that its sharp edge just enters the shaping cone tangentially. The pencil is inserted into the sharpener and rotated while the sharpener is held motionless. The body of the sharpener is often contoured, ridged or grooved to make the small block easier to firmly grip, and is typically made of aluminum alloy, magnesium alloy or hard plastic.
The blade inside the sharpener shaves the wood and graphite tip of the pencil, while the shavings emerge through a slot along the blade edge. It is important that the cylindrical alignment hole closely fit the diameter of the pencil, to keep the pencil from wobbling, which would cause stepped or lurching cut-depths and point breakage. Another important feature is a larger clearance hole at the end of the cone allowing sections of the pencil lead which break away to be removed with only minor inconvenience. Prism sharpeners can be bare or enclosed in a container to collect the shavings, while some enclosed sharpeners may be harder to clear in the event of a blockage. A few prism sharpeners are hand-cranked, rotating the cutting blade instead of rotating the pencil. Moderate care is needed to not break the tip of the pencil being sharpened, requiring the pencil to be sharpened again. However, because pencils may have different standard diameters in different nations, imported sharpeners may have non-standard-sized alignment guide-holes, making sharpening attempts difficult. If the alignment hole is too small, the pencil cannot be inserted, while if it is too large, the tip of the pencil repeatedly will break off. Prism sharpeners may be right- or left-handed, requiring clockwise or counter-clockwise rotation of the pencil being sharpened.
=== Linear blade sharpeners ===
Unlike prism sharpeners, linear blade sharpeners do not rotate relative to the pencil being sharpened, and may be viewed as just a special form of knife, with a mechanical guide for increased safety and convenience. Some models use replaceable shaving razor blades, while others have permanently-fitted blades. Linear blade sharpeners may require more skill, but they allow one to sharpen the tip of the pencil into any desired shape and angle of taper, whereas prism sharpeners have a fixed sharpening angle and produce circular symmetry.
While most linear blade sharpeners are simple and directly hand operated, some devices in the past were crank operated, using mechanisms to convert crank rotation into linear motion.
=== Cylindrical (planetary) sharpeners ===
These mechanisms are also called planetary sharpeners, They work on the same principle as manual ones, but the cylindrical cutter is (or cutters are) rotated by an electric motor. Some electric pencil sharpeners are powered by batteries rather than being plugged into a building's electrical system, making them more portable.
Auto-stop electric pencil sharpeners are able to sense when the tip of the pencil is long enough and then stop. In basic automatic pencil sharpeners the lead may become too long and break, and so users must be careful to time the action.
== Razor knife == Artists and craftspersons may use a very sharp knife to sharpen pencils and other media freehand, without the use of any mechanical guides. For example, the tip may be cut into a triangle shape, and then the edges of the triangle are trimmed down. This requires a total of 6 cuts and takes practice to master without breaking the lead.
== Specialized pencil sharpeners ==
Specialized sharpeners are available that operate on non-standard sizes of pencil, such as crayons used in primary schools. Sharpeners that have two openings, one for normal pencils and one for larger crayons, are fairly common.
An artist's or draftsman's pencil sharpener leaves the graphite untouched and sharpens only the wood (some models can switch from standard to wood-only by an adjustment). The graphite lead is then honed to a sharp point with a lead pointer, which sharpens only the lead without wood. Lead pointers are also used with mechanical lead holders, which have removable/refillable leads. Some sharpeners which function as a long point sharpener, have a second hole in which the blade sharpens the untouched graphite to a long, more precise point than would be otherwise possible using a single hole long point sharpener.
Carpenters may use carpenter pencils, the flattened shape of which stops them from rolling away, while still providing a constant line width. These pencils were traditionally sharpened with tools conveniently to hand, such as a plane or sandpaper. Rotating pencil sharpeners are now available for these, in which a rotating plastic collar holds the pencil in position, although they then sharpen them to the usual conical point as for a round pencil, abandoning some distinctive aspects of the carpenter's pencil.
Sharpeners with a single blade for use on wax crayons are available, and sometimes included in boxes of crayons. These often have plastic blades, which are adequate for the soft wax.
Mechanical pencils dispense the graphite lead progressively during use and thus do not require sharpening; such pencils are sometimes called "self-sharpening". A type of mechanical pencil has a rotating gear mechanism which rotates the lead slightly every time the lead is lifted off the paper, helping to maintain a consistent, sharp point. If a finer or broader line is needed, a separate mechanical pencil using a lead with a different diameter is required.
* [http://www2.mmae.ucf.edu/eml4024-06su/Kyle_Hallenbeck/Write%20Up.htm The Electronic Pencil Sharpener] * [http://therateinc.com/office/best-electric-pencil-sharpener-reviews Top 10 Best Electric Pencil Sharpeners In 2016] *[http://www.officemuseum.com/pencil_sharpeners.htm Antique Pencil Sharpeners] *[http://www.lolomolubdo.com/ Collector of pencil sharpeners] (in French and partly in English) *[http://home.wxs.nl/~joanko/pencil_sharpeners_collection.htm Dutch Collector of pencil sharpeners]
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