The first step in making pencils is the preparation of the graphite center, or "lead." Graphite is a dark, soft mineral which is ground and added to clay and water in a mixing chamber. After the water is squeezed out, the remaining graphite/clay compound is allowed to air dry until it becomes a powder again. This graphite powder is mixed once again with water to form a soft paste. The graphite paste is then extruded through thin metal tubes to form pencil-sized rods. These rods are superheated to create hard and smooth pencil leads.
Meanwhile, a woodworking machine slices blocks of cedar wood into thinner slats. Another machine cuts eight grooves across the length of these slats. Pencils are not carved from a single blank, but actually start out as two half-blanks glued together. As the two halves of the pencils are sandwiched and glued, another machine places a graphite rod on each of the eight shallow grooves. The entire slab of uncut pencils is allowed to dry before further processing.
A special cutting machine receives the uncut sandwiches of wood and graphite, then blades trim down the sides of the pencils to form the familiar hexagonal or round shape. The cutting machine also snaps the slab into individual pencils. Sanding machines smooth out the surfaces of the pencils and prepare them to receive several coats of paint. It is not unusual for pencils to receive up to eight coats of paint to produce the splinter-free surface necessary for safe use of the product.
The painted pencils then receive a hot-stamp pressing usually containing the manufacturer's name and a number corresponding with the relative hardness of the graphite lead. The most common hardness has a designation of #2, but pencils with hardness levels up to #4 can often be found in hobby or office supply stores. Hardness in pencils generally means how much graphite is released per stroke. The higher the hardness number, the less graphite is released, which results in a lighter line.
Traditional wooden pencils are still manufactured in a process first introduced in the 1600s. Modern woodworking machines and automation methods have definitely streamlined the manufacturing process, but most of today's pencils do not vary much from their centuries-old predecessors. Essentially, pencils are the end result of a sandwiching process involving graphite and slabs of cedar wood.
Source: Wisegeek
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