Milling lumber at the sawmill
Sawyers use several different techniques to get boards from a log, depending on the quality of the log, as well as the purpose of the final product. The most common method of milling lumber is slicing a log through its length. The resulting boards are plain-sawn (also called flat-sawn). Plain sawn boards can be flitch cut or "cut for grade".
In flitch cut boards, the wood is plain sawn, with each cut made one
after the other, like slicing a loaf of bread the long way.
This
method has the least amount of waste, but the quality of the wood will
be inconsistent and most boards will contain both heartwood and sapwood.
A stack of boards cut in this manner, from the same log,
is called a flitch. A flitch has the advantage of having matching grain
through out.
Another method of milling lumber into plain
sawn boards is to make a preliminary cut, then roll the log to find the
best face for the second cut.
By rolling the log, the sawyer gets the highest quality board from the
log. This is called cutting for grade (lumber is graded according to the
quality of the board).
With this method the boards will
be of different widths, but the quality will consistently be the best
possible from the log. Cutting for grade thus produces a higher quality
of board, but there is more waste than in simply flitch cutting the log.
Another method of milling lumber results in quartersawn lumber.
As the name suggests, the log is first quartered lengthwise, then boards
are cut from those quarters in such a way that the grain of the
resulting boards is along a plane that passes lengthwise from the bark
edge to the pith of the log, that is, the board is cut radially to the
growth rings.
These different methods of milling lumber make a difference in both the looks and the strength of the board.
A board has three planes.
It has two edges, two ends and two faces. Each of these three planes
absorbs and releases moisture at a different speed, due to the
orientation of the wood cells. Depending on the way a log is cut these
planes will come from different areas of the trunk of the tree.
Imagine a flatsawn board and it’s three planes.
First,
the edge of the board is roughly perpendicular to the growth rings.
This is the radial plane. The radial plane is a section passing from
bark to pith. The grain in this orientation is called edge grain
(sometimes, radial grain).
Second, the ends of the
flatsawn board are in the transverse plane, or cross section. If you
were looking down on a log this is what you would see. This is the end
grain.
Third, the face of the board is roughly parallel
to the growth rings in the tangential plane. If you stripped off the
bark from the length of a log you’d see this plane. When people talk
about grain and figure this is usually what they are referring to.
Now look at the grain of quartersawn wood while thinking about the different planes of wood.
Plain
sawn wood has face grain that is roughly parallel to the growth rings.
Quartersawn wood, on the other hand, has face grain generally 60º-90º to
the face of the board. This gives quartersawn wood the straightest
grain, which also makes it more stable.
Quartersawn
wood is also beautiful. In some species, like oak, quartersawn wood
shows ray fleck. Ray flecks are lines, or rays, of lighter wood
sprinkled throughout the grain. This makes for beautiful,
straight-grained wood.
However, milling lumber into
quartersawn wood is time consuming and creates the most waste, making it
more expensive than plain sawn or flitch cut wood.
For more on the way trees grow click
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