Lumber:
Lumber is a generic term that applies to various lengths of wood used as construction
materials. Pieces of Lumber are cut lengthwise from the trunks of Trees and are
characterized by having generally rectangular or square cross sections, as opposed
to poles or pilings, which have round cross sections.
Lumber produced in early Sawmills:
Had varying dimensions depending on the customers specific order. Lumber pieces used
in construction have standard dimensions and are divided into three categories,
depending on the thickness of the piece.
Pieces of Lumber Surfaced and Machined:
To produce a specific cross sectional shape are classified as worked Lumber or
pattern Lumber. Decorative molding, tongue-and-groove flooring, and shiplap siding
are examples of pattern Lumber.
Produces construction Lumber, Plywood, Fiberboard, Paper, Cardboard, Turpentine,
Rosin, Textiles, and a wide variety of industrial chemicals.
Raw Materials:
The Trees from which Lumber is produced are classified as hardwoods or softwoods.
During felling, the Trees are cut down with chain Saws and the limbs are removed.
At the mill, the Logs are debarked and bucked, or cut to a predetermined length.
Then they proceed to the bandSaw for further processing.
During felling, the Trees are cut down with Chain Saws:
And the limbs are removed. At the mill, the Logs are debarked and bucked, or cut
to a predetermined length. Then they proceed to the bandSaw for further processing.
Which they shed in the winter. Hardwood Trees include oaks, maples, walnuts, cherries,
and birches, but they also include balsa, which has one of the softest and lightest
of all the woods. Softwood Trees include pines, firs, hemlocks, spruces, and redwoods.
Hardwoods are generally more expensive than Softwoods:
And are used for Flooring, Cabinetry, Paneling, Doors, and Trimwork. They are also
extensively used to manufacture Furniture. Hardwoods are available in lengths
from 4-16 ft (1.2-4.8 m). Softwoods are used for wall Studs, Joists, Planks,
Rafters, Beams, Stringers, Posts, Decking, Sheathing, Subflooring, and Concrete
forms. They are available in lengths from 4-24 ft (1.2-7.3 m).
Defects include Knots, Holes, Pitch Pockets, Splits:
And missing pieces on the Edges or Corners, called Wanes. These defects primarily
affect the appearance, but may also affect the strength of the piece. The higher
Grades are called select Grades. Hardwoods may also be Graded as firsts or seconds,
which are even higher than select. The higher the Grade, the fewer
the number of defects.
The lower Grades are called Common Grades:
And are used for general construction where the wood will be covered or where
defects will not be objectionable. Common Grades are designated in descending order of
quality by a number. Pieces of softwood common Grade Lumber may also be designated
by an equivalent name, such as select merchantable, construction, and so on.
Lumber intended for uses other than construction, such as boxes or ladders,
are given other grading designations.
The Manufacturing Process:
Here is a typical sequence of operations for processing Trees into Lumber.
Felling:
Selected Trees in an area are visually inspected and marked as being ready to be
cut down, or felled. If a road does not already exist in the area, one is cut and
Graded using bulldozers. If operations are expected to extend into the rainy season,
the road may be graveled, and culverts may be installed across streams
to prevent washouts.
Most Tree felling is done with gasoline Powered Chain Saws:
Two cuts are made near the base, one on each side, to control the direction the
Tree will fall. Once the Tree is down, the limbs are trimmed off with chain Saws,
and the Tree is cut into convenient lengths for transportation.
If the Terrain is relatively level:
Diesel powered tractors, called skidders, are used to drag the fallen Tree sections
to a cleared area for loading. If the terrain is steep, a self-propelled yarder is used.
The yarder has a telescoping hydraulic Tower that can be raised to a height of 110 ft
(33.5 m). Guy wires support the Tower, and cables are run from the top of the Tower
down the steep slopes to retrieve the felled Trees. The Tree sections, or Logs,
are then loaded on trucks using wheeled Log loaders.
The trucks make their way down the Graded road:
And onto public highways on their way to the Lumber mill. Once at the Mill, Giant
Mobile unloaders grab the entire truck load in one bite and stack it in long Piles,
known as Log Decks. The Decks are periodically sprayed with water to prevent the
wood from drying out.
Debarking and Bucking:
Logs are picked up from the Log Deck with rubber-tired loaders and are placed on
a chain Conveyor that brings them into the mill. In some cases, the outer bark of
the Log is removed, either with sharp-toothed grinding wheels or with a jet of
high-pressure water, While the Log is slowly rotated about its long Axis. The
removed bark is pulverized and may be used as a fuel for the mill furnaces
or may be sold as a decorative garden mulch.
The Logs are carried into the mill on the Chain Conveyor:
Where they stop momentarily as a huge circular Saw cuts them into Predetermined
Lengths. This process is called Bucking, and the Saw is called a bucking Saw.
Headrig Sawing large Logs:
If the Log has a diameter larger than 2-3 ft (0.6-0.9 m), it is tipped off the Conveyor
and clamped onto a moveable carriage that slides lengthwise on a set of rails. The
carriage can position the Log transversely relative to the rails and can also rotate
the Log 90 or 180 degrees about its length. Optical sensors scan the Log and determine
its diameter at each end, its length, and any visible defects. Based on this information,
a computer then calculates a suggested cutting pattern to maximize the
number of pieces of Lumber obtainable from the Log.
Depending on the size of Log:
It may be cut in different ways to optimize the size and number of resulting boards.
After boards are cut, they are dried and planed or rotated to make subsequent cuts.
The headrig Sawyer must constantly review the Log for internal defects and modify
the cutting pattern accordingly as each successive cut opens the Log further. In general,
thinner pieces destined to be made into boards are cut from the outer portion of
the Log where there are fewer knots. Thicker pieces for dimension Lumber are cut next,
While the center of the Log yields stock for heavy timber pieces.
Planing:
The dried pieces of Lumber are passed through Planers, where rotating cutting heads
trim the pieces to their final Dimensions, smooth all four Surfaces,
and Round the Edges.
Grade Stamping and Banding:
Each piece of Lumber is visually or mechanically inspected and Graded according
to the amount of defects present. The Grade is stamped on each piece, along with
information about the moisture content, and a mill identification number. The
Lumber is then bundled according to the type of wood, Grade, and moisture content,
and the bundle is secured with steel bands. The bundle is loaded on a truck or
train and shipped to a Lumber yard for resale to customers.
Quality Control:
There are very few pieces of perfect Lumber. Even though great care is taken to avoid
or minimize defects when Sawing the wood to the required sizes, there are almost
always some defects present. The number and location of these defects determines
the Grade of the Lumber, and the purchaser must choose the Grade that is appropriate
for each specific application.
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