For the machine used to make joints using wooden biscuits or plates, see
Biscuit joiner A jointer is a woodworking machine used
to produce a flat surface along a board's length.
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.
Design Fundamentally, a jointer consists of two
long, narrow parallel tables in a row with a cutter head recessed between
them. This cutter head is typically driven by an electric induction motor. A
moveable fence is normally set perpendicular to the tables, though some
may be adjusted to various angles. The two tables are referred to as the
infeed and outfeed. The work piece to be planed flat is placed on the infeed
table and passed over the cutter head to the outfeed table.
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.
The infeed and outfeed tables can be raised or lowered independently of each
other and in relation to the cutter head although the outfeed table is normally
set so that it is level with the knives when at the top dead centre of the
rotation of the cutter head. The infeed table is adjusted so that it is lower
than the outfeed table and this gives the depth of cut.
Jointers for home workshops usually have a 4–6 inch width of cut. Larger
machines, often 8–16 inches, are used in industrial settings.
Operation In operation, the board to be jointed is
held with its face against the fence and the edge to be jointed resting on the
infeed table. The board is fed across the cutter head and onto the outfeed
table. The knives in the revolving cutter head remove an amount of material
and the relationship of the two tables and the fence keeps the board oriented
in such a way that the result is an edge which is flat along its length and
perpendicular to the board's face. A jointer may also be used to flatten
the face of a board, in which case the sole focus is to produce a flat surface
on the face of the board and the fence is not used. This procedure is often
performed prior to edge jointing so that the board has a flat reference face for
subsequent operations. To straighten a piece of bowed timber,
the guard is temporarily swung out of the way. The machine is switched on and
the timber is slowly lowered to the machine table, with the concave side
down. A few cuts are made out of the red section "A". The timber is turned end
for end and the same procedure is done to the section "B". This is repeated as
required with the operator sighting along the length of the timber from time
to time to check on straightness of the timber. When the timber is almost
straight, the guard is replaced and the last cut is made in the normal way.
Twisted material is treated in a similar way. The operator lays the timber on the
bed of the machine and rocks it slowly from side to side to estimate the amount
of twist. If there is, say, 20mm of twist in the board, he holds the board
level and takes 10mm off one end, then repeats it for the other end.
Jointers are also used for making rebates in finished timber. The fence is
set to the width of the rebate and the infeed table is set to the depth. A
jointer that is used for rebating has the outside ends of its blades also
sharpened and set with a small clearance from the cutter head.
A jointer cannot be used to create a board of even thickness along its
length. For this task, after jointing one face, a thickness planer is used.
Thickness planers and jointers are often combined into one machine, with the work
piece passing underneath the same rotating blade for thicknessing, but in
the opposite direction. In the US this is called a planer–thicknesser or
over-and-under. Linguistic note
"Planer" is the normal term in the UK and Australia for what is called a
"jointer" in North America, where the former term refers exclusively to a
thickness planer. Also some of the older woodworkers use the term "joiner".
See also Thickness planer
References