How to Choose Lumber for Woodworking

The names are botanical, not a measure of hardness: the Wood Handbook defines softwoods as wood from gymnosperms, mostly conifers, and hardwoods as wood from flowering trees, and notes that not every softwood is soft nor every hardwood hard. What matters at the yard is that each is sold differently.

Hardwood grades describe how much of a board can be cut into clear pieces, not how the whole board looks: FAS must yield at least 83-1/3% clear-face cuttings from boards at least 6 in wide and 8 ft long, No. 1 Common about 66-2/3% from boards 3 in wide and up. For parts cut into short lengths, a Common grade may yield every clear piece a project needs; long, wide, clear parts are what the higher grades guarantee. The full rules — with their many species exceptions — are the National Hardwood Lumber Association's. Sizes, surfacing and grades in more detail are in the lumber guide, and every size on the lumber dimensions chart.

• Hardness and density. Dent resistance is on the Janka hardness scale; weight follows specific gravity, which the wood weight calculator turns into pounds for a given board.
• Stability. Every species shrinks most along the growth rings (tangentially) and about half as much across them (radially). A low ratio of the two, and quartersawn stock, mean less cupping. The wood movement calculator estimates how much a panel will move for a given species.
• Figure and grain. Plainsawn boards show the growth rings, quartersawn boards show ray fleck in oak and stay flatter — see wood grain.
• What the project is. Shop jigs and painted work rarely need clear, figured stock; a tabletop that will be seen and handled does. The calculators in this series carry Wood Handbook data for 28 common North American species, hardwoods and softwoods.

Wood shrinks and swells as it loses and gains moisture below about 30% moisture content, so it should be close to the moisture it will settle at in service before it is cut into parts. The Wood Handbook's recommended values for interior woodwork and furniture at the time of installation are:

Construction lumber can therefore be wetter than these values when bought. To know, measure: a sample can be weighed, dried in an oven until its mass stops falling and weighed again, and the wood movement calculator works out the moisture content from the two masses.

• Sight along it for bow along the face, crook along the edge and twist; lay it on a flat surface and look under it for cup. Short parts can be cut from a bowed board; a twisted one loses thickness in flattening.
• Check the ends. End checks are drying cracks that open in from the ends; cut the board off beyond them, and allow for that length.
• Look at the end grain to see whether it is plainsawn or quartersawn, and at the face for knots, pitch pockets and wane — bark or a missing corner along an edge.
• Watch the grain line. Grain that runs out of a board's edge (diagonal grain) shrinks and swells atypically and weakens the piece, and a log with spiral or interlocked grain cannot give straight-grained boards at all.
• Rough or surfaced. A rough surface hides colour and some defects, and rough boards need a jointer and planer, or hand planes, to bring them to size; surfaced boards are thinner than their quarter size (4/4 is 13/16 in S2S).

Hardwood is priced by the board foot: work out the board feet in a list of parts with the board foot calculator, and the pieces to buy and their cost — by the board foot, linear foot or piece, with a waste allowance — with the lumber calculator. Lay the parts out first with the cut list optimizer, and count sheets of plywood with the plywood calculator; the actual thickness of a sheet is on the plywood thickness chart. If you mill your own logs, board feet in a log by three log rules are in the log board foot calculator.

• Reference: the lumber guide, wood grain, lumber dimensions, plywood thickness, Janka hardness.
• Calculators: board feet, lumber, logs, wood weight, wood movement.
• Build: live-edge projects.