The jointer is a machine used for power planing the edges and faces of wood stock. When using rough cut lumber, it is necessary to straighten a board by trueing one face and one edge before ripping to width or surfacing to thickness. This planning is usually done with a jointer before a board is used on a table saw or surface planer.
The process involves trueing one face of the board followed by straightening an edge that is perpendicular to the face. Then the straight edge can be used against the rip fence on a table saw to cut a parallel edge when cutting the board to width. Finally it can then be run through a surface planer to the desired thickness.
A jointer works by pushing the board over a rotating cutterhead with two or three or more knives. On some newer jointers, a cutterhead with a spiral set of knives is available that uses more of a shearing actions resulting in a smoother cut.
The size of a jointer is usually measured by the width of the cutterhead. Common sizes of jointers for the home shop are the 4, 6 and 8 inch jointer. Some commercial jointers come in 12" and wider versions. The width of the knives determines the maximum width of a board that can be joined.
Another way that jointers are measured is by the length of the tables. You'll hear the term short bed and long bed jointer to indicate a longer table measurement.
Four inch jointers are too small for most surfacing, however you do see many four inch jointers in home shops. Six inch jointers are more commone in home shops but at six inches, the widest board you can face is only six inches wide. That means that for stock that goes into wider surfaces, such as table tops, will have to be ripped to width, jointed, and then glued together to make a wide board. Eight inch jointers will obviously handle a wider board for facing. Eight inch jointers are usually longer too which means you can joint longer boards.
The typical jointer is made up of a base, the rotating cutterhead, an infeed table and an outfeed table and a jointer fence. The cutterhead and blades face and rotate toward the infeed table. A piece of wood is edged by feeding it through on edge with one of the faces held againts the jointer fence. The jointer fence is usually set a 90 degrees to produce square faces and edges, but it can be tilted to any disired angle to produce beveled edges.
The depth of cut is set by raising or lowering the infeed table below the top of the fixed jointer knives mounted in the cutterhead. The depth of cut is the difference between the height of the knives and the top of the infeed table.
Other Features That Matter
On most jointers, the tables slide up and down on dovetail ways. On a parallelogram jointer, the table sits on eccentric bushings that can be turned to raise or lower each table at any of four points.
It will appear on your page as: