Jointer

A jointer or in some configurations, a jointer-planer (also known in the UK and Australia as a planer or surface planer, and sometimes also as a buzzer or flat top) is a woodworking machine used to produce a flat surface along a board's length. As a jointer, the machine operates on the narrow edge of boards, preparing them for use as butt joints or gluing into panels. A planer-jointer setup has the width that enables smoothing ('surface planing') and leveling the faces (widths) of boards small enough to fit the tables.

The jointer derives its name from its primary function of producing flat edges on boards prior to joining them edge-to-edge to produce wider boards. The use of this term probably arises from the name of a type of hand plane, the jointer plane, which is also used primarily for this purpose. The surface planer is a wider

Fundamentally, a jointer's table arrangement is designed with two levels like a narrower thickness planer so that it consists of two long, narrow parallel tables in a row with a cutter head recessed between them, but with a side guide. This cutter head is typically driven by an electric induction motor. (Older machines were driven by belts from line shafts.) A moveable fence is normally set perpendicular to the tables, though some models may allow settings (adjustments) to various angles.

These tables are referred to as the infeed and outfeed, the table from which the work piece is fed into the machine and the height reference table on which the work piece is floated over lightly as leaves the machine's cutting head. The cutting blades are adjusted to match the height and pitch of (& made square to) the outfeed table. The work piece to be planed flat is placed on the infeed table and passed over the cutter head to the outfeed table, with care taken to maintain a constant feed speed and downward pressure.

The cutter head contains two or more knives which are honed to a very sharp edge. The knives are arranged radially in the cylindrical cutter head such that their cutting edges protrude from the cutter head so that they will come into contact with the board being cut as the cutter head spins. The cutter head's axis of rotation is parallel to the table surfaces and perpendicular to the feed direction. The knives cut into the board in the direction opposite to the feed.

Some, more expensive, jointer models contain a spiral, or helical, cutting head. This configuration has many individually mounted, self-indexing knives that can be rotated to a new edge when necessary. Other, older, models have cutter heads that are not cylindrical but instead square. This leaves a significantly larger open region below the level of the blade edges and creates a larger hazard as hands, etc., can be pulled in further and cut more deeply.

...
Wikipedia