Aside from proper machine set-up, the most important aspect of planning or jointing wood is
knowing how to "read" the wood grain and being familiar with the characteristics of the wood you're using. If you misread the grain or misfeed the stock, the machine could ruin your workpiece…in a hurry.
Although it may sound a bit strange, planning or jointing wood is a lot like petting a cat. Stroking a cat's fur in the wrong direction will make it stand up and look awful. However, stroking it in the right direction will make the fur lay flat and smooth.
Like the fur of a cat, the grain of wood generally lays in one direction. And as machine knives rotate, they must stroke the wood in that same direction (See Fig. 1). This is called feeding the wood with the grain.
If you feed a board with the grain running in the wrong direction…or feed it too fast for the grain pattern…the knives will dig under the annual rings and tear out chunks of wood. Instead of cutting a smooth surface, your machine will leave the board torn, chipped and rougher than when you started working it. The general rule for feeding a board into the machine is simply that "The knives should stroke the wood…not ruffle its fur!"
The nature f wood grain is determined by several factors: the annual rings; how the board was cut; from what part of the tree the board was cut; and other natural phenomena such as curls, burls and bird's eyes.
You must be able to recognize all of these qualities before you plane or joint any board.
To determine general grain direction, look at the edge of the board that's perpendicular to the edge you want to plane or joint. If the grain is obscured by mill marks or rough sawing, joint or hand plane the edge just enough to remove whatever's obscuring your view (See Fig. 2). Look down the edge of the board for the lines created by the annual rings. These line will show you the general direction of the grain.
As you'll notice, the annual ring lines will either follow an edge…or lead off toward one face or the other. Wavy grain may lead first to one face, then curve back to the other (See Fig. 3). Look for the general direction these lines take. This will determine the direction that you should feed the board into the knives of the machine. 
Finding the general grain direction is just the first step. A board may also have knots, crotch figuring, burls, bird's eyes or a curly grain pattern. Some boards may even have two or more of these characteristics, and each must be taken into consideration.
KNOTS are extremely hard and the grain within each knot runs at an angle to the grain surrounding the wood. This angle may be slight…or it may be nearly perpendicular to the overall grain direction. To avoid tearing a knot, feed the board so the knives stroke the grain and don't attempt to lift and tear it.
CROTCH FIGURING is the transition between the knot and the wood around it. It's not as hard as 
the knot, but it's harder than the surrounding, straight-grained wood. (The grain pattern is highly figured - erratic and wavy - but it follows one general direction.) In this case, feed the wood so the knives stroke in this direction (See Fig. 4).
BURLS are hard, dense clusters of undeveloped knots, surrounded by figured wood similar to crotch figuring. The grain direction is totally random. Because of this, burls are extremely difficult to plane or joint. It's important to take very shallow cuts at a very slow feed rate in order to give the knives a chance to cut properly (See Fig. 5). 
BIRD'S EYES are tiny knots, similar to the center of a burl, randomly distributed throughout a board. The grain of bird's eyes all tend to follow the same direction. This will determine how you feed the board into the machine (See Fig. 6).
CURLY GRAIN patterns grow in pronounced waves that follow a general direction through the board. Because the waves are so exaggerated, the board may be difficult to plane. Feed the board in the 
direction indicated by the general grain direction, and take very shallow cuts at a slow feed rate (See Fig. 7).
Since many types of grain may exist in a single board, the overall grain direction may be completely different at each end. If you have a board like this, reading the grain can be more art than science.
Look at the entire board and try to average out the effects of the different grain patterns. Do your best to determine the feed direction. Then make your first cut with a very shallow depth-of-cut at a very slow feed rate. If the board chips or tears, reverse the feed direction and try again. If the board still chips or tears, check your machine knives for alignment and sharpness. Sharp knives and a precise setup are absolutely essential for the best results.
Once you're getting good results on one side of your board, you're ready to start machining the other side. But don't panic! The second side is always easier than the first. Just flip your board over , turn it end-for-end and feed it through using the same machine settings.
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