Muscles or electricity are required to power a saw, but the sawteeth really do the cutting, reducing the fibers of the material that is being cut to dust. Different classes of saws are manufactured to accomplish different purposes, and the configuration of the teeth on the cutting edge of the saw (whether it's a hand- or power-saw, a circular saw, or a reciprocating saw) are designed and ground for specific uses.
In comparing handsaws, one of the first distinctions you'll notice is the number of teeth per inch. A handsaw with, say, eight teeth per inch will saw more quickly than one with twelve teeth per inch. However, the coarser teeth will also leave a rougher cut surface. Finer cutting saws, in general, make a neater cut but do so more slowly.
The nomenclature of blade-making can get unnecessarily complicated, but a couple of technical terms are useful. There is an easy logic, so saw talk needn't be confusing.
The sawteeth on a saw blade work by making two grooves in the material being cut. The sawdust is pushed out of the resulting kerf by the bevels on the teeth. In handsaws (and some circular saw blades) the teeth are alternately bent (or “set”) beyond the plane of the blade itself, meaning that the cut made by the teeth is wider than the body of the blade.
Another tooth term worth knowing is gullet. Several names for parts of the teeth are self-explanatory, like face, back, and point. But the trough between teeth is called the gullet.
Handsaw Teeth. The basic kinds of teeth on handsaws are these:
Crosscut. The knifelike teeth on a crosscut saw are angled at about seventy degrees to the length of the blade. Typically, there are ten or twelve beveled points per inch. Other kinds of handsaws, like Japanese saws and backsaws, generally have more teeth per inch.
Rip. Ripsaw blades are designed to cut parallel to the grain, so ripsaw teeth are square, ground perpendicular to the length of the blade. Five or six points per inch are usual.
Think of the distinction this way: Crosscut teeth are shaped like knives, to cut across the grain; ripsaw teeth are more like chisels, so that they can chop through the wood along the grain.
Handsaws can be re-sharpened. Files and other accessories are sold to assist in that task. However, saw-sharpening requires practice and precision, so it may be better left to the pros.
Circular Saw Blades. Due to the speed at which the blades spin and the fact that they are ground onto a round blade, circular sawteeth differs from those on handsaws. The same rule of thumb regarding number of teeth holds true (the more teeth, the finer the cut) but because circular saws are sold in a variety of diameters (ranging up to 10, 12, and even 15 inches for large miter and radial arm saws), teeth-per-inch comparisons are not applicable. Rather, you need to compare the number of teeth on a given blade to those on another of the same diameter. Thus, a seven- and-a-quarter-inch blade might have anywhere from 16 teeth to 200, depending upon its quality, kind, and use.
The common circular blades are these:
Combination. Most circular saw blades sold today are com¬bination blades. Designed to cut hard or soft wood, either with or across the grain, the combination blade features both rip and crosscut teeth with deep gullets between them.
Not all combination blades are the same, as some so-called master combination blades have deeper gullets and others have shallower gullets. “Expansion grooves” are cut into the body of some saws to dissipate heat. Some blades have set teeth, while others are termed hollow-ground, meaning the body of the blade is thinner than at the edge; a cut made with a hollow-ground blade looks as if it were planed (hence the other name of planer blades for hollow-ground blades). A fine combination seven-and-a- quarter-inch blade has 40 teeth; coarser general-purpose blades have fewer teeth, sometimes as few as 16.
Rip and Crosscut Blades. These blades are designed to cut with the grain and across the grain, respectively. As with handsaw blades, rip and crosscut teeth are ground differently: Rip teeth cut parallel with the grain, crosscut teeth at an angle. Rip teeth are generally larger and crosscut teeth finer.
Plywood and Veneer Blades. These fine-toothed crosscut blades will cut all sorts of woods, but are specifically designed for cutting plywood. A minimum of splintering of the surface veneer occurs be¬cause of the set and the sheer number of the sharpened teeth. In a seven-and-a-quarter- inch blade, 200 teeth are usual.
Carbide Blades. Carbide or tungsten-carbide blades are not actually different types of blade; their names refer to the materials used in the hardened tips that have been at¬tached to their teeth. They outlast traditional steel blades and though they are more expensive to purchase, generally prove more economical over the long run.
Carbide blades can be bought in a confusing variety of tooth configurations. The different kinds are identified by the way the carbide tips are ground. For example, the “flat top” is for ripping, the “triple chip” for ripping hardwood, the “alternate-top bevel” for cutoff work, and on and on. A 36 or 40 toothed ATP (alternate top bevel) will perform the widest range of cutting tasks.
When buying circular saw blades, select tooth configurations that are best suited to your needs. Be aware, too, that the arbor on your saw (the shaft that passes through the center hole on the blade) is not always the same, so buy the one that fits your specific tool. Five-eighths of an inch is the most common arbor size in portable circular saws.
As with handsaws, some circular saw blades can be reset and re-sharpened. Again, a professional can probably do it faster and better than you can and at a reasonable price.