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Section 4 Manufacturing Process Database
When wood is purchased as rough stock, the
first step is usually to create a smooth surface on
opposing faces by removing a small amount of stock
using the process called planing. Edges are then
smoothed using another process called jointing. Let
us take a closer look at how this process works.
Planing
Machine planing, or surfacing, is a process that
mills wood to a uniform thickness and produces a
smooth surface. Planing is used to remove rough
mill marks on stock that has not been surfaced at the
mill. Planing is also used to true-up (eliminate bow
in) the wood, but it cannot straighten warped stock.
Most stock purchased directly from the mill
needs to be planed to produce smooth faces.
Normally, planing is done in the direction of the
grain, with a maximum cut of 1/16″ (1.6 mm).
There are three major types of machines used
for planing: the knife-blade planer, the abrasive belt
planer, and the jointer. Both the knife-blade and abra-
sive belt planers are used to smooth the face surfaces
of stock. The jointer can be used to surface the faces
of narrow-width stock (boards up to 6″ or 8″ wide).
The jointer is the preferred machine for removing
stock from the edges of boards.
Knife-Blade Planer
Figure 21-1 illustrates the design of a knife-
blade planer, which works on the same principle as
the hand plane. The knife blades shear off a uniform
layer of stock as the material is passed through the
machine. Knife-blade planers with cutterheads
only on the top are called single planers or single
surfacers, and are the most common type. Double
planers have blades on the top and bottom, so that
both sides of the stock can be planed at the same
time. With either type of planer, stock is pushed into
the machine on a bed, and power feed rollers carry
it through the machine. Chip breakers and pressure
bars help to reduce chattering and keep the stock
from jumping during planing.
Planers are sized by the bed width, which essen-
tially means the width of stock that can be milled in
the machine. Planers range in bed width from 12″ to
52″ (30 cm to 132 cm). Knife-blade cutterheads are
normally adjustable to suit the width of the stock to be
planed. Cutterheads may carry a number of knives, or
may have only one, with a counterbalancing blank on
the other side of the planer head. Large planers may
carry as many as 20 or 30 jointed knives. Figure 21-2
shows an operator planning a thick board on a single-
surface knife-blade planer.
One of the disadvantages of the knife-blade
planer is that the knives must be removed for
sharpening and changes in set-up. The practice is
Figure 21-1. A single surfacer is a knife-blade planer with
one rotating cutterhead. The knife blades, held in place by
plates called gibs, shear off a thin layer of material from the
top of the stock as it passes through the machine. Units with
two cutterheads, called double planers, surface both top
and bottom of the stock at the same time.
Outfeed roll
Pressure bar
Gib
Cutterhead
Knife
Chip breaker
Infeed roll
Stock
Figure 21-2. This worker is feeding a thick plank through a
knife-blade planer. Note the vacuum system used to collect
sawdust and chips attached to the top of the machine. It
simplifies cleanup and minimizes the amount of dust in the
air. (Delta International Machinery Corporation)