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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 case around them which can be removed for emptying the pencil shavings debris into a trash bin.
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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, though 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. Electric pencil sharpeners for offices have been made since at least 1917.
In May 2011, tourism officials in Logan, Ohio put on display, in its regional welcome center, hundreds of pencil sharpeners which had been collected by Rev. Paul Johnson, an Ohio minister who died in 2010. Johnson, a World War II veteran, had kept his collection of more than 3,400 sharpeners in a small shed, outside his home in Carbon Hill in southeast Ohio. He had started collecting after his wife gave him a few pencil sharpeners as a gift in the late 1980s. He kept them organized into categories, including cats, Christmas, and Disneyland. The oldest was 105 years old.
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 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. Some enclosed sharpeners may be harder to clear in the event of a blockage.
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. A few prism sharpeners are hand-cranked, rotating the cutting blade instead of rotating the pencil. 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 directly hold replaceable shaving razor blades, while others have permanently fitted blades. 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, in reference to their use of planetary gears. A larger, stationary planetary sharpener can be mounted on a desk or wall and powered by a hand crank. Typically, the pencil is inserted into the sharpener with one hand, and the crank is turned with the other. This rotates a set of helical cylindrical cutters in the mechanism, set at an acute angle to each other. The multiple cutting edges quickly sharpen the pencil, with a more precise finish than a single-blade device. Some cylindrical sharpeners have only one helical cutter cylinder, but most have two cylinders or more. Most planetary sharpeners have a large opening, with a rotatable guide disk in front of it that has multiple holes of different sizes, to accommodate pencils of many different diameters.
Advanced models have a spring-driven holder for the pencil, so that the pencil automatically is pushed into the mechanism while being sharpened. Some versions also offer a regulator of the desired sharpness, since it is not always desired to make the graphite core needle-sharp. Planetary sharpeners may be very easy to use even by children, but are usually more expensive than prism sharpeners. The casing of the sharpener collects the pencil shavings, and needs to be emptied periodically.
Other systems
Some older models like the 1897 German Jupiter 1 used reversible rotary cutter-disks with cutting edges radiating from the center on each side. These were high-end models, quite large and expensive. Others simply used abrasives like sandpaper. In some cases an abrasive was used to shape the graphite core, while the wood was cut some other way.
Electric sharpeners
Electric pencil sharpeners 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 the large art pencils used in primary schools. Sharpeners that have two openings, one for normal pencils and one for larger art pencils, 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 razor point with a lead pointer which sharpens only the lead without wood. Lead pointers are also used with mechanical leadholders which have removable/refillable leads.
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 too, where 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 all the distinctive aspects of the carpenter's pencil. A different design uses a sliding guide, which more closely mimics whittling the pencil by hand using a sharp knife.
Sharpeners with a single blade for use on wax crayons are available, and sometimes included in boxes of crayons. These often have plastic blades for the softer wax.
Mechanical pencils dispense the graphite lead progressively during use and thus do not require sharpening; such pencils are sometimes called "self-sharpening". If a finer or broader line is needed, a mechanical pencil using a lead with a different diameter is required.