Woodworking Tools
Board foot arithmetic, cut lists and joinery proportions — starting with the two places wood quietly goes missing: the dressing that makes a 2x4 into 1.5 by 3.5, and the blade that turns every cut into sawdust.
A 2x4 delivers 65.6% of the wood its name implies, and 4/4 hardwood is billed 33% above what it hands you.
Cut List OptimizerA 96-inch board gives seven 12-inch pieces, not eight. On thin strips the blade costs several — 144 inches into 2-inch pieces loses five.
Wood Movement CalculatorQuartersawn moves half as much — on average. On white pine it saves 2.9x and on birch only 1.3x, so the rule is per species.
Joinery Proportion CalculatorThe one-third tenon rule is a derivation, not a tradition: x = (t-x)/2 solves to exactly t/3, where the tenon equals one mortise wall.
Compound Miter CalculatorThe bevel formula with cos(180/N) agrees only at four sides and is up to 75 degrees out elsewhere. Verified against 3D geometry.
Segmented Turning Ring CalculatorA ring has 2N cut faces, so error multiplies by 2N. Half a degree out on 12 segments leaves a 12 degree gap — more segments is worse.
Router Bit Speed CalculatorThe speed chart on your router is one number in disguise — a constant rim speed. A 3.5-inch bit at full speed is 14x a quarter-inch one.
Shelf Sag CalculatorSag goes as span to the FOURTH power. A centre support beats doubling the thickness two to one, and one extra foot outweighs the material.
Wood Finish Coverage CalculatorSize a tin properly: both faces, all four edges, end grain counted triple, and multiplied by the coats you actually intend to apply.
Shellac Cut CalculatorWeigh flakes for any cut, dilute between cuts, and see why a 5-pound cut is only 3.3 times the concentration of a 1-pound one.
Epoxy Pour Volume CalculatorVolume for a river table pour, how many layers the depth limit forces, and why a 2:1 mix by volume is 2.35:1 on a scale.
Lumber Drying Time CalculatorThe year-per-inch rule against a diffusion model, which squares the thickness — and why resawing before the stack quarters the wait.
Dust Collection CFM CalculatorDuct sizing for a shop dust system, including the ceiling nobody expects: a duct can be too WIDE and silt up.
Pilot Hole CalculatorPilot and clearance sizes from your own screw measurements, and why skipping the clearance hole stops the joint closing.
About these woodworking tools
Two separate things quietly remove wood between the yard and the workbench, and both are larger than they sound. The first is dressing. Everyone knows a 2x4 is really one and a half by three and a half, and almost nobody multiplies it out — the shortfall applies to BOTH dimensions and cross-section is a product, so the nominal eight square inches becomes 5.25 and you receive 65.6 per cent of the wood the name implies. A third of it is not there. Nor is the fraction constant, which is what catches people substituting one size for another: a 1x2 delivers 56.3 per cent and a 6x6 delivers 84.0, because a fixed quarter inch off each face costs far more on a small section than a large one. Hardwood does the same thing through a different door. It is billed by the board foot at ROUGH thickness, so a 4/4 board is charged as one inch and surfaces to three quarters — an 8 inch by 8 foot board is billed 5.33 board feet and hands you 4.00. You pay for 33.3 per cent more wood than you receive, which is not a swindle, since the planing is real work and the shavings are real wood, but it is a third and it belongs in the estimate rather than in the surprise at the till. That gap narrows as boards get thicker — 75 per cent at 4/4, 87.5 at 8/4 — which is a real argument for buying thick and resawing. The second thief is the blade. Pieces per board is not stock divided by piece, because every cut but the last consumes a kerf: it is the stock plus one kerf over the piece plus one kerf, which is why a 96 inch board yields SEVEN 12 inch pieces rather than eight. Swept over 925 realistic stock-and-piece combinations at an eighth-inch kerf, 12.8 per cent lose a whole piece — about one in eight, though it feels commoner because the familiar cases happen to be among them. On thin strips it is worse than one piece, which is the part that surprised us: total sawdust is the cut COUNT times the kerf, so it grows while each piece stays small, and ripping 144 inches into 2 inch strips gives 67 rather than 72. Five pieces, nine inches, gone to dust. Everything here is quantity and layout rather than structural design — species strength, span and load are questions for a span table or an engineer, not a calculator.