The choosing of blades for their saws is a frequent problem among woodworkers. Whether they are using a table saw, band saw, circular saw, or jigsaw, most woodworkers are always on the lookout for saw blades that provide the smoothest, most precise cuts imaginable. The number of teeth per inch (TPI) on a blade has a significant impact on the quality of a cut. The rule of thumb is "the greater the TPI, the finer the cut." The correct answer, however, is a bit more involved, as you will discover after you comprehend how to saw teeth function.
How Saw Teeth Cut
Each tooth on a saw blade is effectively a little, sharp chisel that excavates wood fibres as the blade passes through a material. Typically, the greater the number of teeth on a saw blade, the smoother the cut. This is true for the majority of saws, including the table saw, mitre saw, circular saw, jigsaw, scroll saw, and band saw. However, these flawless cuts come at the expense of speed, as blades with several teeth must cut slowly to attain their exquisite finish. Fewer-toothed saw blades will cut more quickly and aggressively but will yield generally rougher finishes. On a blade with fewer teeth, the crevices (gullets) between the teeth are deeper and the chiselling action of the tooth is more aggressive, resulting in each tooth removing a greater amount of wood. At the same feed rate, a fine-tooth blade with a high TPI count brings more teeth to bear on the cut, so that each tooth is responsible for cutting a lesser amount of wood.
The obvious consequence of a rough-cut blade with fewer teeth and a greater cutting speed is that the cuts will be harsher. Due to this, rough-cut blades with a lower TPI count are typically designated for framing carpentry or for cutting non-visible workpieces. In fine woodworking with hardwoods, smoothness of cut is of more importance, thus blades with a high TPI count are utilized more frequently. Fine-toothed blades offer a smoother cut but come at a price. Due to the slower and less forceful nature of the cuts, there is a larger chance that the wood will be burned by friction when the blade passes through the workpiece. Cutting using a fine-tooth blade increases the probability of binding since the gullets between the teeth are very narrow and don't clear sawdust as quickly.
Other Factors Influencing a Cut's Quality
More aspects influence the quality of a saw blade's cut. The angle of the teeth about the blade's plane is known as the set. A blade with a more prominent set will cut more aggressively, but it will also eat more wood due to its larger kerf. This can be problematic if you're attempting to conserve wood on extremely costly cattle. A blade's sharpness can have a significant effect on the quality of a cut. Due to the ineffective cutting of wood fibres by dull teeth, dull blades are significantly more prone to scorch and burn wood. In addition, a dirty blade can impair the cut. As wood pitch accumulates on the blade's surface, the wood will be more prone to bond and burn. Maintain clean saw blades to guarantee smooth cutting.
Manufacturers offer many types of blades for various cutting applications:
Typically, crosscut blades have a higher TPI count and smaller teeth, which are designed to cut wood perpendicular to the wood grain. Teeth with left-facing bevels are alternated with teeth with right-facing bevels on the tooth tips.
Rip-cut blades have a smaller number of TPI, bigger teeth, and deep gullets between each tooth. They are designed for parallel wood grain cutting. Flat-topped teeth on a rip-cut blade are designed to efficiently split wood fibres.
Combination blades are designed to cross-cut and rip-cut adequately, although neither task is performed as well as with blades designed particularly for the task. They are ideal for general frame construction or for the casual do-it-yourselfer who does not require extreme precision.
Recommendations
As a general guideline, woodworkers should have many blades for each saw in their possession. For example, a 10-inch table saw should be equipped with a 40-tooth blade for regular use, an 80-tooth blade for plywood and veneers, and a specialized ripping blade for rip cuts. On a band saw, keep a few blades of varying thickness and select one based on the sharpness of the curves being cut. Use a 1/4-inch blade for somewhat tight curves, a 1/2-inch blade for typical band saw cuts, and a 3/4- or 1-inch blade for resawing wood stock. The 1/2-inch, 3/4-inch, and 1-inch blades should have three TPI (teeth per inch), whereas the narrower blades should have more teeth per inch.
Keep a variety of blades for hand power tools, such as circular saws and jigsaws/sabre saws, on hand. Circular saw blades are offered in the same varieties as a table saw blades: fine-tooth blades for precise cross-cutting, a coarser blade for rip-cutting, and a combination blade for general framing carpentry. A quality pair of blades for a sabre saw or jigsaw will comprise coarse-tooth blades for fast cutting and rip cuts and fine-tooth blades for clean crosscuts. There are also speciality jigsaw blades for cutting ceramics, polymers, and other materials.
