What Does the Term "Kerf" Mean in Woodworking?

Close up detail of circular saw
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The term kerf is used to describe the thickness of the cut a woodworking saw blade makes in a piece of wood as it cuts through it. The term is also sometimes used to describe the thickness of the blade itself; for example,  you may see the packaging of a circular saw blade or table saw blade listing its kerf width. For example, one manufacturer offers a standard crosscut table saw blade with a kerf of 0.098 inches (2.5mm), while the same manufacturer offers a fine-cut blade with a kerf width of 0.087 inches.

The Importance of Kerf Width

Woodworkers pay attention to kerf width in order to maintain precision when cutting parts for fine woodworking pieces. For projects where precise tolerances are critical, the 0.098 inch of a kerf width can matter when measuring and cutting parts. To a lesser degree, woodworkers are also concerned with the wasted wood that results from blades with thick kerfs. Over time, a substantial amount of expensive hardwood is turned to useless sawdust by saw blades, and the thinner the blade, the less waste there will be. 

Factors Determining Width of a Kerf

The kerf width is most often specified for circular blades, such as that used on table saws, miter saws, and circular saws. While bandsaw blades, for example, also has a kerf width, this is of less concern to woodworkers because bandsaw blades are very thin to begin with and don't waste much wood. 

The kerf is determined by the width of the blade itself, by the "set" of the teeth (the angle away from vertical by which the teeth are attached to the blade), and by the wobble of the blade.

Coarse construction blades often have heavy carbide teeth welded onto a stainless steel disc with a pronounced angled set that allows for quick but rough cutting. These are normally used for framing carpentry work. These blades will have a fairly wide kerf. 

For fine woodworking, it's more common to use thinner blades with many teeth that have little or no angled set.

Often the teeth are not added onto the blade but are integrally shaped into the metal of the blade itself. This makes for a very smooth cut and one that is economical since little wood is wasted through wide kerfs. This can be a relevant factor when working with very expensive exotic woods. 

A saw blade out of alignment will wobble while cutting, and this can increase the width of the kerf by a notable amount. For efficiency of cutting and economical use of wood, always make sure your saw blades are properly aligned.