How lumber is made

A two-by-four is neither two inches nor four inches. It shrank on the way from the log to the store.

stations: 6
things upstream: 1
raw source: 1
step from the ground: 1

The short version

Lumber is a log sawn into boards and beams. A sawmill strips the bark, runs the log through saws that turn it into rough boards, then dries them in a kiln or in open air so they stop warping. Planers smooth the faces to standard sizes, and graders sort every board by strength and defects.

Strip the bark

Logs arrive at the mill and go through a debarker that scrubs the bark off. The bark is not wasted. Mills burn it for heat or sell it as landscaping mulch.

Goes in
Timber
Saw the log into boards

A big saw works its way through the log. Cutting straight through gives plain-sawn boards with the grain running across the width, while turning the log between cuts gives boards whose growth rings stand more upright. Sawing is far quicker than hewing or splitting a log by hand.
Trim and split to width

Edgers square off the wavy sides of each board, and resaws split thick pieces into thinner ones of the same length.
Dry out the boards

Fresh wood is full of water that sits inside its cell walls. Boards are stacked and dried in a heated kiln or left to air-dry, because wood that dries unevenly splits, bows and develops hidden cracks. Dry wood below about 25 percent moisture can stay free of decay for centuries.

below 25% moisture
Plane to standard size

Rotating knives shave the faces and edges smooth. This is where a 2x4 shrinks. Modern standards describe the finished size, and a 2x4 ends up 38 by 89 mm.

38 by 89 mm
Grade every board

Inspectors, or machines that measure stiffness or density, sort the boards by knots, splits and strength. The grade stamp tells a builder how much load a board can be trusted to carry.

End of the lineLumber Next it goes into pencil, kitchen knife, whiskey and 20 more.

Worth repeating

About 80 percent of lumber comes from softwood trees such as pine, fir and spruce.
A Dutch windmill owner built the first wind-powered sawmill in 1593, and it cut logs into planks thirty times faster than hand sawing.
Historically, a board's nominal size, such as 2x4, was the size of the green, rough-sawn board, and finished lumber is smaller than its nominal dimensions after drying and planing.