The jointer is used for the initial stages of machining solid wood. Most of the wood used in the joinery or cabinetmaking shop arrives as rough lumber which is rarely accurate enough to use as is. For accurate and tight fitting joinery, straight, square stock is essential. Even if the stock has been properly surfaced and squared, if left for a period of time, solid wood will continue to move as it comes into equilibrium with the ambient humidity. Tension is released in solid wood as it is further cut to size, often necessitating re-machining.
The purpose of the jointer is to create a flat, true surface free of bow, twist or cup, and to create a straight, square edge relative to a jointed (flat) face. The jointer can also be used for small sizing jobs, (such as fitting cabinet doors), to cut tapers and bevels, and for cutting rabbets (such as for door jambs).