Cut a board one way and it moves a lot. Cut it another way and it moves half as much. Same species, same moisture change — completely different behaviour. The difference is the angle of the growth rings.
In Guide 3, we established that wood moves in three axes and that tangential movement is roughly twice radial movement. That fact alone explains most of the warping, cupping, and seasonal frustration in woodworking.
This guide goes deeper. We’ll look at exactly what tangential and radial mean in a real board, how to identify which direction you’re dealing with, and how to use that knowledge to choose and orient timber for better results.
Defining the Directions
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Image placeholder: Tangential vs radial on a log
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- Clean log cross-section diagram.
- Arrow for radial (pith → bark) and tangential (along ring curve).
Every piece of wood comes from a cylinder — a tree trunk. That cylinder has a centre (the pith) and concentric growth rings radiating outward.
The two directions of significant movement are defined relative to those rings:
Tangential
Tangential means 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
Radial means from the pith outward, crossing the growth rings at right angles.
- On a quarter-sawn board, the wide face is mostly radial
- This is the direction of lesser movement
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Diagram placeholder: Cross-section of a log showing tangential direction (curving along the rings) and radial direction (arrow from pith outward). Label both clearly.
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How to Identify the Direction in a Real Board
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Image placeholder: End-grain ID (flat vs quarter vs rift)
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- 3-panel end-grain photos or diagrams.
- Ring angle labelled on each.
- Optional: matching face-grain thumbnails.
You don’t need lab equipment. You need the end grain.
Look at the end of a board and find the growth ring pattern:
Flat-sawn (tangential face exposed)
- Growth rings on the end grain run roughly parallel to the wide face (or in wide arcs)
- The wide face shows cathedral” or “flame” grain patterns
- This board will move more across its width
Quarter-sawn (radial face exposed)
- Growth rings on the end grain run roughly perpendicular to the wide face (straight vertical lines)
- The wide face shows straight, parallel grain and sometimes ray fleck (medullary ray figure)
- This board will move less across its width
Rift-sawn (intermediate)
- Growth rings on the end grain are at roughly 45 degrees to the wide face
- Movement behaviour is between flat-sawn and quarter-sawn
- Straight grain on the face with minimal figure
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Diagram placeholder: Three end-grain cross-sections side by side — flat-sawn, quarter-sawn, and rift-sawn — showing ring orientation relative to the wide face. Below each, show the corresponding face grain pattern.
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The Numbers: How Much Difference Does It Make?
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Image placeholder: T/R ratio visual
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- Simple bar chart comparing tangential vs radial shrinkage for 3–5 species.
- Highlight that tangential is typically ~2× radial.
Here are some representative shrinkage values (green to oven-dry) for common species to illustrate the tangential-to-radial ratio:
| Species | Tangential shrinkage | Radial shrinkage | T/R ratio | | — | — | — | — | | European Oak | ~8.5% | ~4.5% | ~1.9 | | European Beech | ~11.8% | ~5.8% | ~2.0 | | Scots Pine | ~7.7% | ~4.0% | ~1.9 | | Douglas Fir | ~7.8% | ~4.8% | ~1.6 | | Western Red Cedar | ~5.0% | ~2.4% | ~2.1 | | Black Walnut | ~7.8% | ~5.5% | ~1.4 |
Key observations:
- The T/R ratio is typically 1.5 to 2.5 across most commercial species
- Some species (like walnut) have a relatively low ratio, meaning more uniform movement
- Others (like beech) have a high ratio, meaning flat-sawn boards will move significantly more than quarter-sawn
These are green-to-oven-dry values. In practice, your boards won’t swing through the full range — but the ratio between tangential and radial stays consistent regardless of the MC change.
Why This Matters in Practice
The tangential-to-radial difference has direct consequences for every project.
1. Cupping in flat-sawn boards
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Image placeholder: Cupping mechanism (bark side vs pith side)
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- Cross-section diagram showing bark side shrinking more.
- One real photo of a cupped board if available.
A flat-sawn board has tangential movement across its width and radial movement through its thickness. Because tangential shrinkage is greater, the bark side shrinks more than the pith side.
Result: the board cups away from the bark.
This is predictable and consistent. It’s why woodworkers check ring orientation before gluing up panels.
2. Quarter-sawn boards stay flatter
A quarter-sawn board has radial movement across its width. Less movement means less cupping.
This is one of the main reasons quarter-sawn timber is prized for:
- tabletops
- drawer fronts
- door panels
- flooring
- musical instrument soundboards
The trade-off: quarter-sawing produces more waste from the log, so it costs more.
3. Panel glue-ups
When gluing boards edge-to-edge for a panel:
- Alternating the ring direction (bark up / bark down) does not prevent movement — it just distributes cupping into a wavy surface instead of a single cup
- Selecting boards with similar ring orientation and consistent MC produces a more predictable panel
- All-quarter-sawn panels move the least overall
4. Frame and panel construction
Traditional frame and panel design exists specifically because of tangential movement. The panel floats in the frame, free to shrink and swell, while the frame (usually with grain running along its length) stays dimensionally stable.
If the panel is flat-sawn, the seasonal width change will be larger. If quarter-sawn, smaller. Either way, the panel must float.
Estimating Movement in Real Projects
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Image placeholder: Worked example graphic
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- Simple graphic: 600mm top, ΔMC = 4%, show flat-sawn vs quarter-sawn movement result.
You can estimate seasonal movement using published shrinkage coefficients and expected MC change.
The basic approach:
- Determine the direction of movement on your board (tangential or radial, based on ring orientation)
- Look up the shrinkage coefficient for that species and direction
- Estimate the MC change your piece will experience (based on the EMC range in its environment)
- Calculate:
$$ \Delta W = W \times \Delta MC\% \times S $$
Worked example:
A flat-sawn European oak tabletop, 600mm wide.
- Tangential shrinkage coefficient: approximately 0.00369 per 1% MC change (this is the percentage shrinkage per 1% MC, expressed as a decimal)
- Expected seasonal MC swing: 8% to 12% = 4% MC change
- Movement: 600 × 0.04 × 0.00369 × 600…
Let’s simplify. Oak’s tangential dimensional change is roughly 0.37% per 1% MC change.
- 4% MC change × 0.37% per 1% MC = 1.48% total change
- 1.48% of 600mm = ~8.9mm
That’s nearly a centimetre of seasonal movement. Now compare with quarter-sawn oak (radial, roughly 0.19% per 1% MC change):
- 4% MC change × 0.19% = 0.76%
- 0.76% of 600mm = ~4.6mm
Half the movement — same species, same width, same environment. The only difference is how the board was cut from the log.
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The Timber Logic movement calculator (coming soon) will do this maths for you. But understanding the principle is more important than the numbers.
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Practical Guidelines for Choosing and Orienting Timber
When stability matters most, choose quarter-sawn
- Wide tabletops
- Drawer fronts that must stay flat
- Door panels
- Flooring (less 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
- Multiple narrow boards glued together are more stable than one wide board
- Allow for seasonal movement in fixings and joinery
For the best compromise, consider rift-sawn
- Movement is moderate
- Grain is straight and consistent
- Good for table legs, chair parts, and anything where twist would be a problem
Always check the end grain
Before you buy, before you mill, before you glue — look at the end grain and know what direction you’re working with.
Common Mistakes This Knowledge Prevents
- Ignoring ring orientation when gluing up a panel — ending up with a tabletop that cups dramatically in winter
- Using flat-sawn boards for wide, unsupported surfaces — when quarter-sawn would have halved the movement
- Not leaving expansion gaps — especially in flat-sawn flooring, where tangential movement can close gaps and buckle boards
- Expecting all boards to behave the same — two boards from the same plank can have different ring orientations and move differently
The Simple Rule
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Always check the end grain. Tangential moves the most, radial moves the least. Choose your cut angle to match how much movement you can tolerate.
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What’s Next
We’ve now covered tangential and radial movement in detail. But there’s a third direction we mentioned briefly — longitudinal. In Guide 5 — Longitudinal Movement (and Why It’s Small), we’ll explain why wood barely changes length, what the rare exceptions are, and why this fact is actually the foundation of many joinery techniques.
🔗 Knowledge Network
Species Pages
- European Oak — T/R ratio ~1.9, tabletop movement worked example
- European Beech — high T/R ratio ~2.0
- Scots Pine — T/R ratio ~1.9
- Douglas Fir — T/R ratio ~1.6
- Western Red Cedar — T/R ratio ~2.1
- Black Walnut — low T/R ratio ~1.4, more uniform movement
Glossary Terms
- Tangential
- Radial
- Flat-sawn
- Quarter-sawn
- Rift-sawn
- T/R Ratio
- Shrinkage Coefficient
- Cupping
- Medullary Rays
- Ray Fleck
Calculators
- Movement Calculator — explicitly referenced as “coming soon” in this guide
Categories
- Tangential vs radial movement
- Ring orientation
- Quarter-sawn vs flat-sawn
- Wood movement basics
- Seasonal movement
- Timber selection
Related Guides
- Track 2 – Guide 3 – Why Wood Moves — the mechanism behind all wood movement
- Track 2 – Guide 5 – Longitudinal Movement (and Why It’s Small) — the third axis of movement
- Track 2 – Guide 6 – Shrinkage and Swelling — full shrinkage values and how to read them
- Track 1 – Guide 10 – How Logs Become Boards — grain orientation and its effects
- Track 1 – Guide 5 – Growth Rings Explained — understanding the ring structure that defines tangential vs radial
- Track 4 – Guide 2 – Plain Sawn vs Quarter Sawn vs Rift Sawn — the sawing methods that produce these different cuts