A planer thicknesser is a woodworking power tool designed to produce boards of constant thickness and perfectly flat surfaces. It is a table tool meaning that it is a non-portable, floor mounted device featuring a working mechanism mounted on an adjustable, flat working surface or table. Planer thicknessers consist of four basic components: a height adjustable table, a cutting head perfectly perpendicular to the table, a set of in-feed rollers, and a set of out-feed rollers. The machine functions by automatically feeding the board across the table, thereby shaving a nominal amount of material off it as it passes the cutting head. If required, the board is then turned over and the process repeated which produces a product that is flat and of equal thickness across its entire surface.
Carpentry and cabinet making projects often require a machine which can cut large boards to various thicknesses, can produce those thicknesses equally across the entire board, and achieve perfectly flat surfaces. The planer thicknesser, often called a thicknesser planer, is such a machine. This machine is equipped with a wide cylindrical cutting head featuring two or more longitudinal cutting blades. The cutting head is positioned above and perfectly perpendicular to a flat working table which may be height adjusted to cater for various thicknesses of finished board. Two sets of rollers, one in-feed and one out-feed set, on either end of the table automatically feed the board across the table and under the cutting head.
As the board passes under the cutting head, a certain amount of material is cut away over its entire surface by the cutting head. Due to the flat table surface, perpendicular orientation of the cutter, and the cutter pressure, the board is kept flat during the cutting pass. Once the cut is complete, the board may be turned over and fed through the planer thicknesser to cut the opposite side if required. This produces a board which is the exactly the same thickness across its entire face with perfectly flat surfaces.
The planer thicknesser works best if one side of the board is relatively flat and uniform to begin with. This will generally allow for the board to be finished in a single pass. If a board is warped, it should be passed through a jointer or power plane first to reduce the deflection. If this is not done, the pressure of the cutting head on the planer thicknesser will simply push the board flat during the pass, only to have it regain its curvature when it exits the machine. Planer thicknesser machines are fairly dangerous if used incorrectly; operators should always follow standard operating procedures and wear hand, eye, and ear protection at all times.