Flatsawn, Quartersawn, Riftsawn: How It Was Cut Decides How Much It Moves

Look at the end of the board. FLATSAWN shows long sweeping arcs of growth ring, often the cathedral pattern on the face. QUARTERSAWN shows rings running nearly straight across the thickness, close to 90 degrees to the face, and often a ribbon of medullary ray flecking on the face in oak. RIFTSAWN sits between, with rings at roughly 30 to 60 degrees. It moves less than flatsawn, does not cup much, and has no ray fleck — which makes it the usual choice for table legs, where a consistent grain on all four faces matters. One board can be all three along its length, because a log is round and a saw cut is straight. Read the end grain at BOTH ends before deciding what a board is.

A flatsawn board cups because its two faces are at different distances from the centre of the tree, so one face shrinks tangentially more than the other. The result is predictable: **the board cups away from the heart side** — the rings try to straighten out. So you can tell which way a board will cup before it does, from the end grain alone. Put the heart side where a cup will do least harm, or where a fixing will hold it. Alternating heart-up and heart-down across a glued panel is the old advice, and it is a compromise rather than a cure: it turns one big cup into a washboard of small ones. Where the face matters, better to use quartersawn stock, or narrower boards, or accept the cup and fasten for it.

QUARTERSAWN: about half the width movement, stays flat, ray fleck in oak, and a more even face. It costs more because the sawyer gets fewer and narrower boards out of a log. Use it for tabletops, drawer sides, panels, anything wide that must stay flat. FLATSAWN: cheapest, widest boards, the most figure, and the most movement and cupping. Use it where width is cheap and flatness is held by construction — narrow parts, carcase sides that are fixed at both ends, anything painted. RIFTSAWN: in between, and the specific answer for square parts like legs, because all four faces show similar straight grain. It is also what you get from riving, which splits along the rays and is why riven timber is so stable.

Plywood barely moves in any direction, because alternate layers have their grain at right angles and each one restrains the next. A sheet of Baltic birch is dimensionally stable in a way no solid board can be. That makes it the correct material for anything wide that must not move — a cabinet back, a drawer bottom, a jig, a router template. Using solid wood there and then trapping it is a common and entirely avoidable failure. The trade is that plywood has no solid thickness to work: it will not take a moulded edge, the exposed edge is ugly and fragile, and it does not hold a screw in its edge well. Which is a design decision — stability against workability — rather than one being better.