A jointer (also known in the UK and Australia as a planer or surface planer, and sometimes also as a buzzer or flat top) is a woodworking machine used to produce a flat surface along a board's length. The jointer derives its name from its primary function of producing flat edges on boards prior to joining them edge-to-edge to produce wider boards. The use of this term probably arises from the name of a type of hand plane, the jointer plane, which is also used primarily for this purpose. Fundamentally, a jointer consists of two parallel tables, a moveable fence which is normally set perpendicular to the tables, and a cutter head which is typically driven by an electric induction motor. (Older machines were driven by belts from line shafts. ) The two tables are referred to as the infeed (table from which the work piece is fed into the machine) and outfeed (table to which the work piece is fed as it leaves the machine). The work piece to be planed flat is placed on the infeed table and passed over the cutter head to the outfeed table. The cutter head contains two or more knives which are honed to a very sharp edge. The knives are arranged radially in the cylindrical cutter head such that their cutting edges protrude from the cutter head so that they will come into contact with the board being cut as the cutter head spins. The cutter head's axis of rotation is parallel to the table surfaces and perpendicular to the feed direction. The knives cut into the board in the direction opposite to the feed. Some, more expensive, jointer models contain a spiral, or helical, cutting head. This configuration has many individually mounted, self-indexing knives that can be rotated to a new edge when necessary. The infeed and outfeed tables can be raised or lowered independently of each other and in relation to the cutter head although the outfeed table is normally set so that it is level with the knives when at the top dead centre of the rotation of the cutter head. The infeed table is adjusted so that it is lower than the outfeed table and this gives the depth of cut. Jointers for home workshops usually have a 4-6 inch (100-150mm) width of cut. Larger machines, often 8-16 inches (200-400mm), are used in industrial settings.
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