A pencil sharpener (also referred to as a parer or topper in Ireland) 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.

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 recently a fixed-blade device with a rotatable collar has become available.

Bernard Lassimone, a French mathematician, applied for the first patent on pencil sharpeners in 1828. In 1847, Therry des Estwaux invented an improved mechanical sharpener[1]. 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

They now come in a wide array of colors and shapes. It is common for traditional sharpeners to have a case around them to collect the shavings. It can be removed for emptying.

A mechanical pencil sharpener is hand-powered. A common, portable variety is usually small and in the shape of a rectangular prism, about 1 × 5/8 × 7/16 inch (2.5 × 1.7 × 1.1 cm) in size with a conical hole on the small end.

A sharp blade is mounted in a recess on the largest side such that its sharp edge just enters the cone. The body of the sharpener is often contoured, ridged or grooved to make it easier to grip firmly. It has no moving parts – the tip of the pencil is inserted into the hole of the sharpener and rotated, while the sharpener is held motionless.

The blade inside the sharpener shaves the wood of the pencil, thus sharpening the tip, while the shavings emerge through a slot along the blade edge. An 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.

Such sharpeners can be bare or enclosed in a container to collect the shavings. Enclosed sharpeners can be harder to clear in the event of a blockage.

The base of such a sharpener is often made of aluminum, magnesium or hard plastic. Skill is needed to not break the tip of the pencil being sharpened, losing the result of work immediately.

While it is more common in sharpeners with cylindrical cutters, some prism sharpeners are also hand-cranked.

Unlike prism sharpeners, blade sharpeners do not rotate around the pencil being sharpened and may be viewed as just a special form of knife with increased safety and convenience.

Some models directly hold replaceable shaving razor blades, 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, whereas prism sharpeners have a fixed sharpening angle and require circular symmetry.

While most blade sharpeners are simple and hand operated, some devices in the past were crank operated, using mechanisms to convert crank rotation into linear motion

A larger, stationary mechanical sharpener can be mounted on a desk or wall and powered by a crank. Typically, the pencil is inserted into the sharpener with one hand and the crank turned with the other.

This rotates a set of cylindrical cutters in the mechanism, set at an angle to each other. This quickly sharpens the pencil, with a more precise finish than the simpler blade device.

Advanced models have a spring – driven holder for the pencil (the pencil advances inside the mechanism while being sharpened). Some versions also offer a regulator of the desired sharpness (it is not always optimal to make the graphite core needle-sharp). Such sharpeners may be very easy to use even by children but are much more expensive than prism sharpeners.

Some such rotary sharpeners have only one burr cylinder. The casing of the sharpener is the repository for the pencil shavings; it needs to be emptied periodically. They are also called “planetary sharpeners”, in reference to their use of planetary gears.
read more at text source