A way of sawing
lumber that produces
boards of
superior quality,
but requires more effort on the part of the
sawyer, and wastes more of
the
tree.
Everyone is familiar with the annual growth rings that all trees get;
however, growth rings are potential sources of weakness in a board.
If rings cross a board diagonally:
_______________
|\ \ \ \ \ \ \ \|
| \ \ \ \ \ \ \ |
|\ \ \ \ \ \ \ \|
| \ \ \ \ \ \ \ |
there is a higher chance that a corner will splinter off, either while
it is being worked, or by use of the finished product. Not only that,
moisture will make the board cup in ways unacceptable for some uses.
In addition, some types of wood split radially, creating more opportunities
for breaks.
Even worse, a board will change shape as it dries out. This movement happens more in the wetter, wider part of the ring resulting from summer growth rather than the darker part of the ring. If the rings in a board's cross section are curved, this will result in "cupping".
____________________
|\\\\\`--------'/////|
|\\\\`----------'////|
|\\\`------------'///|
|\\`--------------'//|
|\`----------------'/|
Because of this, the best boards have their growth rings parallel to
a board face, traveling all the way across the board:
_______________ _______________
| | | | | | | | | |---------------|
| | | | | | | | | |---------------|
| | | | | | | | | |---------------|
| | | | | | | | | |---------------|
| | | | | | | | | |---------------|
Now most boards are is "plain-sawn"; but from the log by a series of parallel cuts, ignoring the tree's growth rings:
_____
-- --
/___________\
/_____________\
|_______________|
|_______________|
|_______________|
\_____________/
\___________/
--_____--
Plain-sawn boards are called "flitch-sawn" when the bark is left on, something handy for boatbuilding.
Although this maximizes the amount of board-feet you can get out of
one log, different areas of the tree will create boards with growth rings
going in various, usually diagonal, directions.
However, you can arrange the saw cuts on a log to take maximum advantage
of the tree's growth ring pattern:
_____
_-- | | --_
/\ \ | | / /\
/ \ \| |/ / \
|____\_| |_/____|
|______| |______|
| / | | \ |
\ / /| |\ \ /
\/ / | | \ \/
--_|_|_--
This is called "quarter-sawing" because the sawyer usually starts the
process by sawing the log into quarters. A really skilled sawyer can get
more boards (unsuitable for drawing with ASCII art) out of the little
wedge-shaped pieces left over, but therein lies the problem. Quarter-sawing requires more skill and care on the part of the sawyer, and it wastes more of the tree. Because of this, quarter-sawn wood is much more expensive than plain-sawn wood. If you go to the sawmill yourself, you are buying the entire tree and getting less out of it.
The question then becomes: When will plain-sawn lumber suffice, and
when does the extra expense of quarter-sawn lumber make sense? You're
certainly not going to frame your house with 2x4's made of quarter-sawn
oak. Building a deck? Kiln-dried and pressure-treated wood has less of a cupping problem. (By the way, framing with post and beam construction has its own requirements). But if you're making a piece of furniture, or
if you want a nice strong keel or mast step for your boat, quarter
sawn lumber is the way to go.