The thickness planer is designed to produce a board of a constant thickness, depending on a movable table and a scale to set the thickness. The table adjusts in height to vary the distance between it and a cylindrical cutter head that is mounted above the table. As wood is fed into the planer it is picked up by a powered feed roller that presses it down and carries through the planer under the cutter head. Any part of that board that is thicker than the distance from table to cutter head will be machined off to produce a constant thickness.

Thickness planers cannot produce a flat board with no warp unless one face has already been flattened with a jointer.