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 bowed timber, the guard is temporarily swung out of the way. The machine is switched on and the timber is slowly lowered to the machine table, with the concave 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. 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 its 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 thickness planer is used.
Thickness planers and jointers are often combined into one machine, with the work piece passing underneath the same rotating blade for thicknessing, but in the opposite direction. In the UK this is called a planer–thicknesser or over–and–under.
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