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The Way Wood Works: Reading Grain Direction


The Way Wood Works: Reading Grain Direction

By Tom Caspar

“Going against the grain” is a familiar phrase. It means doing something the wrong way.When you’re talking about wood, you always want to go with the grain—cutting or planing a board in a way that follows the natural structure of the tree (Photo 1). The result is a smooth surface.

How do you figure out which way the grain goes? Some folks use the coin-toss method.They’ll joint or plane one side in an arbitrary direction and observe the results.After all, you’ve got a 50-50 chance of being right! When you’re wrong,however,you can be really wrong (Photo 2) and you’ll get tear-out.Whether it’s shallow or deep, tear-out means extra work in planing, scraping or sanding a board.

Tear-out will rarely be a problem for you after we show you how to read the fibers inside a board.Most woodworkers think that the ovals or lines on the surface of a board are the key to grain direction, but this type of “grain” is not completely reliable for predicting fiber direction (Photo 3). Going with the grain really means going with the fibers. In the pages to follow,we’ll show you other clues that are more dependable in predicting the fiber direction in hardwoods.

1. Wood is composed of long fibers that typically run at an angle to the surface of a board. Splitting a board reveals the direction of the fibers, but we’ll show you less destructive methods of reading grain direction on the following pages.

Click any image to view a larger version.

2. Nasty tear-out is often the result of planing a board against the grain.The better you get at reading grain direction, the less time you’ll spend sanding out a mess like this.

3. Grain direction can fool you. Normally we call patterns of ovals and lines made by the growth rings the “grain” of the wood.We assume that the fiber direction runs the same way.The split-off piece of red oak at right shows that this “grain” and the fiber direction don’t necessarily go the same way. Small cells called rays are the true indicators of fiber direction in plainsawn oak. (Plainsawn boards are also commonly called flatsawn boards. See below for more information on rays and plainsawn boards.)

4. Feel the fuzz on rough lumber. No kidding, you can tell which way to plane rough lumber merely by running your hand over it! The direction that the fibers go feels smooth, while the opposite direction feels rough and jagged.That’s because many individual fibers actually stick out above the surface of rough lumber.You’re feeling their sharp ends.

5. Know where to look. On smooth lumber, the clues to fiber direction are on the surface of the wood.

You can’t read fiber direction just by looking at the surface you want to plane, however. The clues to look for are on the edge adjacent to the surface you’ll plane.To plane the top (1), look at the side (2).To plane the side, look at the top.

6. Rays are the best clues to fiber direction in hardwoods. The general angle of the rays on the plainsawn face of a board invariably point in the same direction as the wood’s fibers.This typical piece of red oak is easy to read because oak’s rays are quite prominent. Beech and sycamore also have large rays. Cherry, maple and many other woods have rays that are paler and much smaller, but you can find them if you look closely. Some hardwoods, such as ash and walnut, have rays that are too small to see.

7. Look for vessels to indicate fiber direction when you can’t see rays.Vessels are cells that look like long, dark dashes.They’re easy to spot on this piece of walnut once you know what you’re looking for. Mahogany, butternut and birch also have clearly visible vessel cells, as do many other woods.

8. Figure is a last resort. If you can’t see rays or vessels, go with the angle of the dark lines that most woodworkers call the “grain” of a board. (“Figure” is the more accurate term.) We’re all familiar with the concentric growth rings on the end of a board (Photo 9). If you follow those rings around to the face or edge, they become the lines and ovals that lend each board a distinctive figure.

9. Fiber direction can often run two ways. Tearout may be inevitable no matter which way you plane this board, but you can minimize it using the clues to fiber direction given here. In this piece of ash, the figure made by the growth rings is the only obvious clue to follow.The angle of this figure is steeper at one end of the board than the other.Always use the steeper end to decide which way to plane.

10. Mark fiber direction on the end of the board.This mark means “begin planing the top surface here.” It can’t be accidentally removed as you mill the faces or edges of your lumber.

What are rays?

Ray cells radiate from the center of a tree.These long, thin ribbons show different faces depending on how the board is cut from the tree.

You can clearly see the wide side of the rays when the surface of a board runs at a right angle to the growth rings.This surface is called a quartersawn or radial face, and the ray’s wide sides are called ray fleck.

When the surface of a board runs more or less parallel to the growth rings, you only see the narrow ends of the rays.This is how most boards are sawn, and this surface is called a plainsawn, flatsawn or tangential face.

This story originally appeared in American Woodworker September 2003, issue #102.

September 2003, issue #102

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