Jointer

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For the machine used to make joints using wooden biscuits or plates, sometimes incorrectly referred to as a biscuit jointer, see Biscuit joiner

Jointer

A jointer (also known as a planer, surface planer, buzzer, or flat top) is a woodworking machine used in woodworking to produce a flat surface on a board.

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.

[edit] Design

Fundamentally, a jointer consists of two parallel tables - the infeed and outfeed tables - a moveable fence which is normally kept perpendicular to the tables, and a cutter head which is driven by some form of mechanical motorisation, commonly today an electric induction motor.

The cutter head contains 2 or more knives which are sharpened to a fine cutting 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 set parallel to the table surfaces and perpendicular to the feed direction. The knives cut into the board in the direction opposite to the feed.

The infeed and outfeed tables are capable of being raised or lowered independently of each other and in relation to the cutter head. The outfeed table is 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.

[edit] Operation

In operation, the board to be jointed is held with its face against the fence and the edge to be jointed resting on the infeed table. The board is fed across the cutter head and onto the outfeed table. The knives in the revolving cutter head remove an amount of material and the relationship of the two tables and the fence keeps the board oriented in such a way that the result is an edge which is flat along its length and perpendicular to the board's face.

A jointer may also be used to flatten the face of a board, in which case the sole focus is to produce a flat surface on the face of the board and the fence is not used. This procedure is often performed prior to edge jointing so that the board has a flat reference face for subsequent operations.

To straighten a piece of bent timber, the guard is temporarily swung out of the way. The machine is switched on and the timber is slowly lowered to the position in the above sketch, with the hollow side down. A few cuts are made out of the red section "A". The timber is turned end for end and the same procedure is done to the section "B". This is repeated as required with the operator sighting along the length of the timber from time to time to check on straightness of the timber. The operator should be careful not to apply pressure in the middle of the work, and force it into a false straightness. When the timber is almost straight, the guard is replaced and the last cut is made in the normal way.

Twisted material is treated in a similar way.The operator lays the timber on the bed of the machine and rocks it slowly from side to side to estimate the amount of twist. If there is say 20mm of twist in the board, he holds the board level and takes 10mm off one end, then repeats it for the other end.

Jointers are also used for making rebates (also known as rabbets in North America) in finished timber. The fence is set to the width of the rebate and the infeed table is set to the depth. A jointer that is used for rebating has the outside ends of it's blades also sharpened and set with a small clearance from the cutter head.

A jointer cannot be used to create a board of even thickness along its length. For this task, after jointing one face, a thicknesser can be used.