Perhaps the most disheartening of these is splintering a board as you get near the end of the cut. It’s going fine, and then part way through, the fibers tear out, and you’re left with a splintered, rough-looking edge. This is because wood is not a consistent medium. It’s a group of long fibers running parallel to each other, and when you cut from one side, so that the fibers on the other side aren’t backed up as you cut, they pull up and break instead of cutting. Being able to determine the direction of the grain before you make a cut is probably one of the first techniques that will help you go from occasional success to consistent success.
First, inspect the board surface. Lines that appear as wavy, or like flattened ovals, show the direction of the grain just below. Always cut with the grain when you can; that is, cut in a direction that lets the teeth pull fibers apart. If the grain rises toward the far edge of the board, that edge is likely to tear out. A pencil mark along the safer direction helps avoid confusion when the tools come out.
Try this exercise to develop your sense of this. Cut three or four different scraps of wood, with prominent grain, shallow cuts, in the same direction. Now cut them again going the other way. And for bonus credit, feel the cuts, try to see with your fingertips. I guarantee you that in less than 15 minutes you’ll appreciate the difference. You’ll also appreciate the fact that you need to slow down to pay attention to all these things.
Another misconception is that a sharp tool is all you need to avoid tearing. A sharp tool is important, but so is your technique and the use of support. Exerting extra downward pressure as you near the end of a cut frequently aggravates the tear by folding the fibers over before they break. Rather, ease up on the pressure as you near the end of the cut and use a scrap board placed as close as possible to the back side of the cut to support the fibers. This backer board will enable the tool to cut through both boards and minimize tearing.
This is a very minor detail, but scoring the surface before making a cut also helps. By gliding a knife along the line you want to cut before you actually make the cut, you are making sure that the fibers on the surface will not be able to tear away. It takes a few seconds to do, but it can make a huge difference, especially on hardwoods. Once you get in the habit of doing this, you’ll find that tearout ceases to be random and becomes somewhat predictable. This makes certain “brittle” boards much easier to cut, because you can start to anticipate what will happen when you make a cut.