The two directions, defined by the rings
Every board comes out of a cylinder. That cylinder has a centre — the pith — and concentric growth rings radiating outward. Both directions of significant movement are defined against those rings.
- Tangential
- Along the curve of the growth rings — tangent to them. On a flat-sawn board, the wide face is mostly tangential. This is the direction of greatest movement.
- Radial
- From the pith outward, crossing the rings at right angles. On a quarter-sawn board, the wide face is mostly radial. This is the direction of lesser movement.
Reading it off the end grain
Nothing more than a look at the end of the board. Find the growth ring pattern and work out the angle to the wide face.
- Flat-sawn — tangential face exposed
- Rings run roughly parallel to the wide face, or in wide arcs. The face shows cathedral or flame figure. Moves more across its width.
- Quarter-sawn — radial face exposed
- Rings run roughly perpendicular to the wide face — straight lines. The face shows straight parallel grain, sometimes ray fleck. Moves less.
- Rift-sawn — intermediate
- Rings sit at roughly 30–60 degrees to the wide face. Movement falls between the two, with straight grain and little figure.
Worth doing before you buy, before you mill, and before you glue anything up — a five-second check that decides how the finished piece behaves for the rest of its life.
The numbers, and why they’re a ratio not a figure
Published shrinkage values from green to oven-dry show the difference. Figures for species you’re likely to meet, with the ratio that matters:
- European oak
- Tangential around 8–9%, radial around 4.5% — a T/R ratio near 2.
- European beech
- Tangential around 11–12%, radial around 6% — a high ratio, and flat-sawn beech moves noticeably more than quarter-sawn.
- Douglas fir
- Tangential around 7–8%, radial around 4–5% — a lower ratio near 1.6, so the two directions sit closer together.
- Western red cedar
- Tangential around 5%, radial around 2.5% — a ratio near 2, but both figures low, which is part of why it’s so well behaved.
Two things to take from that. The T/R ratio is typically between 1.5 and 2.5 across most commercial species — a narrow band, and remarkably consistent. And a lower-ratio species moves more uniformly, while a high-ratio species makes cut angle matter more, not less.
These are green-to-oven-dry approximations, varying by source, growth conditions and where in the log the board came from — your boards won’t swing through the full range. But the ratio holds regardless of how much moisture changes, and the ratio is what tells you what you gain by choosing a different cut.
Where this shows up in practice
Cupping. A flat-sawn board has tangential movement across its width and radial through its thickness. Because tangential shrinkage is greater, the bark side shrinks more than the pith side — so the bark-side face goes concave and the board cups away from the heart. Predictable, consistent, and the reason to check ring orientation before gluing up a panel.
Quarter-sawn stays flatter because its width is radial, and radial moves less. That’s why it’s prized for tabletops, drawer fronts, door panels and flooring. The trade-off is honest: quarter-sawing takes more out of the log, so it costs more.
Panel glue-ups. You’ll often hear that alternating ring direction — bark up, bark down — cancels movement out. It doesn’t cancel the movement across the width: the panel still shrinks and swells by the same amount. What it does is stop the cups adding up. Each board still cups a little, but the panel ends up with a gentle ripple instead of one big curve, which is why it’s so widely recommended. The trade-off is that ripple: fine in a frame or a top held down with buttons, more of a nuisance on a surface you’ll want to keep dead flat. Either way, choosing boards with similar ring orientation and consistent moisture content helps the panel move predictably rather than fighting itself.
Frame and panel construction exists specifically because of tangential movement. The panel floats, free to shrink and swell, while the frame stays stable along its length. Either way the panel has to float.
Estimating movement on a real job
Four things get you a working estimate: the direction (from ring orientation), the species and its shrinkage coefficient for that direction, the moisture change the piece will see, and the width — movement scales with it.
Take a flat-sawn oak tabletop, 600mm wide, in a heated UK home swinging 8% to 12% — a four-point change. Oak’s tangential movement works out at roughly 0.30% per point, so four points gives about 1.2% of the width: roughly 7mm.
Now cut the same board quarter-sawn, where the figure is nearer 0.16% per point. Four points gives about 0.64%, and 0.64% of 600mm is roughly 4mm.
Half the movement. Same species, same width, same room, same year — the only difference is the angle of the growth rings. That’s the whole argument for thinking about cut angle when you’re buying rather than when you’re building.
There’s a movement calculator that runs this for you: pick the species, the width and the moisture range, and it returns expected movement as a range. Treat it as an estimate rather than a promise — it’s built on typical figures for a species, and any individual board can differ.
Choosing and orienting
When stability matters most, choose quarter-sawn. Wide tabletops, drawer fronts that must stay flat, door panels, flooring where you don’t want seasonal gapping, instrument tops.
When figure and cost matter more, flat-sawn is fine — but plan for movement. Narrower boards move less in absolute terms, and several narrow boards glued together stay flatter than one wide one, though the panel still moves across its full width. The oak page covers what to look for in a board if you want the species-specific side.
For the middle ground, consider rift-sawn — moderate movement, straight consistent grain, and a good choice for table legs, chair parts and anything where twist would be the problem.
And whatever you choose, check the end grain before you buy, before you mill, before you glue up.
Mistakes this prevents
- Ignoring ring orientation when gluing a panel. You end up with a tabletop that cups dramatically in its first winter.
- Flat-sawn boards on wide unsupported surfaces where quarter-sawn would have halved the movement.
- Assuming all boards behave alike. Two boards from the same log can have different ring orientations and move differently — which is why sorting them before a glue-up matters.
The rule worth keeping
Always check the end grain. Tangential moves the most, radial the least. Choose your cut angle to match how much movement you can live with.
Next in the track
Tangential and radial are now covered properly. What’s left is the third direction — mentioned and set aside twice already. Why does a board barely change length, what are the rare exceptions, and why is that fact the foundation of so much joinery? That’s Track 2, Episode 5: Longitudinal Movement (and Why It’s Small).