Modern woodworkers benefit from the speed and efficiency of power tools; power saws are among the most useful. A clear understanding of the kerf of the saw blade and how it affects the dimensions of a cut helps keep measurements accurate. Knowing whether your saw cuts a wide or a narrow kerf improves your knowledge of your tools, and ultimately sharpens your woodworking skills.
What Is the Kerf?
The kerf of a saw blade refers to the width of the cut produced by the blade. It usually is a bit wider than the body of the blade itself, because the teeth of a saw blade tend to flare to one side or the other, away from the central axis of the width of the blade. The amount of flare can vary from blade to blade, depending on manufacturer, type of saw and type of blade. Blade manufacturers usually list the kerf measurement on the blade packaging and/or mark it on the saw blade itself.
Table Saw Blades
Typical table saw blades tend to have a fairly wide kerf, because the blade is made to cut a variety of materials. It's also made to both rip wood (cut it in the direction of the grain) and to make crosscuts (cut it across the grain). The blade therefore has a sturdy, wide body and teeth offset to get through hardwood, softwood and sheet goods quickly and powerfully.
Circular Saw Blades
Blades designed for hand-held circular saws are smaller than table saw blades, and usually have thinner blade bodies, too. They therefore cut a narrower kerf. This allows the saw to use less energy to get the blade through the wood, since hand-held circular saws have less power than stationary table saws.
Both table and hand-held circular saw blades are available for cutting materials that are prone to splintering and chipping, such as plywood, particleboard or laminate. Often labeled as "hollow ground" blades, these tend to have a fairly narrow kerf, as well as many small teeth to keep the edge of the cuts smooth. These blades won't cut material as quickly, so if you're using a table saw, you'll have push the wood through the saw more slowly. If you're using a hand-held circular saw with a hollow ground blade, you'll have to push the saw through the wood at a slower rate.
Measuring for the Kerf
Take the kerf of the saw blade into account when you're measuring and marking your cuts. Blade manufacturers will usually include the kerf measurement either on their packaging or on the blade itself, but it's best to actually cut a test piece of wood when you start using the blade so you can measure the kerf for yourself. For example, if you measure a piece of wood and mark a cut line at 12 inches, you need to be sure to align that mark with the outside edge of the blade. Otherwise, if you simply cut down the center of the mark, the kerf of the blade will take wood away from your measurement, and you'll end up with a piece that's shorter than 12 inches.
When using a table saw, never rely solely on the measurement settings built into the rip fence, the adjustable straight-edged rail you hold the wood against as you guide it through the saw. If you've switched to a blade with a wider kerf, the distance from the edge of the blade to the fence may be different than the settings, and will make your pieces either too long or too short. Instead, use a ruler or square to measure from the fence to the outside edge of the blade, and your cuts will be accurate.