Pencil sharpeners are common fixings around classrooms, artists' studios, and offices around the world. They are designed to provide an easy way for people to bring their graphite pencils to a sharp point. They utilize a number of ingenious solutions in order to fulfill this purpose, and the mechanisms inside your average pencil sharpener are numerous and varied.
Blades - The most important part of the pencil sharpener, without which nothing would happen. They shape the pencil and slice off bits of graphite and wood in order to make your pencil's tip as sharp as possible.
Housing - Where you insert the pencil point in order to get it sharp. The housing is generally every part of the pencil sharpener, aside from the blades, that your pencil or your hands come in contact with.
Crank - In some manual pencil sharpeners, the circular handle you have to turn in order to sharpen the pencil.
Receptacle - Area where shavings are deposited. In many manual pencil sharpeners, there is no receptacle, but in electric sharpeners it's almost a necessity because they produce shavings at such a rapid rate.
Prism - Term used for the smallest, most common, and cheapest manual pencil sharpeners. Their housings are shaped like rectangular prisms - you put the tip of the pencil into the housing and twist until it's sharp.
Planetary Gears - The gears inside a manual cylindrical or rotary pencil sharpener. They are called planetary gears because they consist of two gears rotating around a central gear, like planets revolving around the sun.
There are hundreds of different models of pencil sharpeners, each with its own unique twist on the design. At the heart of a pencil sharpener are the blades. The basic question behind the design of any pencil sharpener is, "how do I use these blades to create a tapered point at the end of a pencil?"
Prior to the invention of the pencil sharpener, people sharpened their pencils by hand, with knives. This was often a lengthy process, and each subsequent design has made the task of sharpening pencils quicker and easier.
The Prism Sharpener
Perhaps the most common sharpener today, the prism sharpener looks like a one-inch by three-quarter-inch by half-inch rectangular prism. It contains a conical housing with two a blade set about 23 degrees at an angle from the line of the pencil. The user twists the pencil into the blade, which cuts away wood until the tip creates an angle of 23 degrees with the pencil, and is tapered to a sharpened point.
The Hand Crank Sharpener
Common in classrooms, the hand crank sharpener utilizes a set of planetary gears with blades attached to the ends of the rotary gears, generally at an angle of 23 degrees. The central gear is connected to a hand crank. The user inserts a pencil into the housing and then turns the hand crank so the blades whip around the pencil, cutting off shavings. Hand crank sharpeners typically don't have shavings receptacles, so they are often placed over a trash bin to catch the wood and graphite shavings that result.
The Automatic Sharpener
Automatic pencil sharpeners tend to look like plastic blocks with a pencil-sized hole in the front and either a power cord or a battery housing on the other end. Inside the hole are one or two blades, again arranged at a 23-degree angle, connected to a pulley system of rods, chains and gears. Electricity is sent to the motor, which transforms the electrical energy into kinetic energy, which is then sent through the system until it reaches the final gears, which turn the blades around the pencil in a similar manner to the hand crank sharpener. Every automatic sharpener uses a different system to transmit the kinetic energy from the motor to the turning blades, so we can't go into more detail than that.
Artist's and Draftsman's Pencil Sharpeners
Because artists need their tips to be extra sharp, artists' pencil sharpeners use separate mechanisms to pare away the wood and sharpen the graphite tip. Lead pointers are used to sharpen the tip, which operate like standard sharpeners except they are adjustable, allowing for different tip angles. Meanwhile, the wood is shaved or simply trimmed and cut away according to the sharpener model. These sharpeners often come in different sizes, as certain specialty pencils are larger or smaller, wider or narrower than standard ones.
Carpenter's Pencil Sharpeners
Carpenter's pencils are flat and designed to keep from rolling away while working. For this reason, they can't be used in standard pencil sharpeners. However, mechanical sharpeners for these types of pencil twist a blade around the tip only, while the housing holds the flat part of the pencil in place.
Old Fashioned Sharpeners
The oldest pencil sharpener utilized metal files set at a 90 degree angle in a block of rosewood. These worked like sandpaper to grind the edges of the pencil's conical tip smooth and clean. While these created a nice, smooth tip that looked uniform, they didn't sharpen as well as the models to follow, which used blades to shave off graphite or lead in a circular motion.
Prior to the use of pencil sharpeners, all around the world people used pen knives to sharpen their pencils. Pen knives were so named because they were used to cut a sharp tip in quill pens, which people still used to write with through the late 1700s and early 1800s. However, these knives were hard to use, and didn't create uniform tips on pencils in the same way they could be used for pens. In 1828, a French inventor and mathematician named Bernard Lassimone patented the first mechanical pencil sharpener. It looked much like the old fashioned sharpener (described above). These were used sparingly because they ended up being more difficult than just using a knife to cut the pencil to a point. They were mostly popular among mathematicians and inventors for the ability to create a smooth cone with a single repeated motion. However, as with many mathematical concepts that aren't initially practical, they paved the way for a later, highly practical invention. In 1847, another French inventor, Therry des Estwaux, created the bladed sharpener that is the ancestor of the prism sharpener we use today. Because these actually created a sharp pencil point much more quickly than Lassimone's, they caught on all over the world. By 1855, Walter Kittredge Foster had created his own version of Estwaux's sharpener as an American patent, and sold them for $10 per gross. Foster died a rich man, in part due to his ability to mass-produce the Estwaux sharpener and in part because he did away with its fancy aesthetic and form. This, too, is present in the legacy of the prism pencil sharpener. Throughout the 19th century, a number of competing models of pencil sharpener, including the expensive German Jupiter 1, which used rotary blades to slice off edges of the pencil tip, were produced, but by 1917, when the first electric pencil sharpener was produced for office use, Estwaux's and Foster's patented models were far and away the most popular.
If the sharpener cuts a dull point or jams up when you try to turn it, the shavings receptacle may be full. This can cause pencil shavings to jam up the gears, which hurts the machine and hurts your pencils in the long run. Empty out the receptacle and if it still doesn't work, try cleaning out the gears to see if there's anything stuck there. If the point is still dull, chances are the blades in your pencil sharpener simply haven't lasted. This is common with cheap pencil sharpeners, and the best solution is to go and buy a new one. With more expensive sharpeners or if you just want to be a DIY-er, you can often take apart the sharpener, unscrew the blades from their gears or the housing, and sharpen them with a small file. For electrical sharpeners: if the unit simply doesn't turn on, chances are there's a problem with the power cord or the connection to the battery. Try replacing the cord or checking the electrical connections from the battery housing to the motor to see if there are any obvious problems. If this doesn't work, there could be a problem with your motor. Motors are broken when an electrical current doesn't get transformed into kinetic energy, so if you send a current that you know is reaching it, and the motor doesn't turn, you need to replace the motor or replace the pencil sharpener.
