Last month, www.cabinetmaker-digital.com/cabinetmaker/200706 we learned the vocabulary of circular saw blades. Now it's time to speak the language.
Let's discuss some of the typical features you should consider when choosing and using circular saw blades in the cabinet shop.
Saw plate thickness
The plate of a saw blade is often 1/8 to 1/4 inch thick. The thinner plate means that there is less sawdust and potentially less waste. However, thin blades, often called thin-kerf blades, are very sensitive to heating and wobbling, which in turn means non-straight (wavy or snaky) cuts. As a result of this one factor, most people opt for a thicker and therefore stiffer plate. When someone comes up with a thin-kerf, stiff plate, it will sell like hot cakes.
Saw tooth design
There are four basic tooth designs for circular saws:
Flat-Top Grind (FTG). These teeth have a flat top and are shaped like miniature chisels. They are fast and are best suited for ripping. It is critical, if the ripped edge will be glued, that side dressing is perfectly done. It is surprising how often saw shops fail to do a perfect job, so the ripped edge quality is poor.
Alternate-Top Bevel (ATB). These teeth, as the name implies, are beveled on the top, with every other tooth being beveled in the opposite direction to the adjacent teeth. The bevel angle can range from 5 to 40 degrees; 10 to 20 degrees is most common. (FTG teeth are 0 degrees.) With this angle, the tooth cuts with a shearing action and this limits tear-out or chip-out. ATB teeth are usually more closely spaced than FTG teeth. ATB blades can be used for ripping and crosscutting.
ATB and Raker (ATB&R). This saw tooth design consists of typically four ATB teeth followed by one raker, which is basically an FTG tooth. With the ATB, the cut is clean, but has a beveled bottom. The raker tooth cleans up the kerf to achieve a flat bottom. This would be important with dado cuts or other cuts that do not go all the way through the workpiece. The 40-tooth ATB blade has replaced this blade in many cases for saws using 10-inch blades.
Triple-Chip (TC). With the triple chip, the teeth resemble those on an FTG blade, but then the outside edges of every other tooth are chamfered at 45 degrees. The tooth that is not chamfered is called a raker tooth. The chamfered tooth makes a rough cut and then the raker cleans up the cut. This blade is especially suited for particleboard cutting. It does okay with solid wood, but not as well as an ATB.
The angle at which the tooth face is at compared to a radius from the center of the plate is called the hook angle. (Rake is the same angle, but usually the term rake is applied to knives.) The larger the hook, the more the blade wants to climb into the wood; a saw with large hook is called an aggressive saw. The large hook also means rougher cuts (that is, more tear-out).
On the other hand, the smaller the hook angle, the more force it takes to push the blade into the wood. In fact, with a radial-arm saw, the hook is usually zero degrees so that the saw does not climb into the workpiece and stall or create a safety issue. However, zero hook for crosscutting and ripping can force the workpiece to come flying back out of the saw toward the operator slow enough that it can be seen but too fast to move out of the way.
For rip saws, the hook is typically 15 to 20 degrees. For crosscutting, 10 to 15 degrees is common.
Preferred saw blades
Certainly there is a lot of debate, but the following are my thoughts about the "best" saws:
Crosscutting solid wood and cutting plywood. ATB with 40 to 80 teeth on a 10-inch diameter blade and 10 more on a 12-inch blade, depending on the quality of the cut required.
Ripping solid wood. ATB with 40 teeth on a 10-inch and 50 on a 12-inch; or FTG with 20 to 30 teeth on a 10-inch and 10 more on a 12-inch.
Cutting composite wood materials. TC with 80 teeth on a 10-inch blade and 90 or more on a 12-inch.
Radial-arm saw. As above but also with zero hook. VERY IMPORTANT!
Although a few saws use steel teeth, almost every modern saw uses carbide tooth tips that are brazed onto the steel body. Carbide consists of a mixture of tungsten, carbon and cobalt. It lasts 50 times longer when cutting wood than steel teeth. Carbide is very brittle, so the saw must be handled very carefully once off the arbor.
There are other materials used for teeth, including diamond and Stellite.
Saw blade quality
With saw blades, the old adage is true: "You get what you pay for." Expensive saws are flat, have quality brazing of the carbide tips and have expansion slots for accommodating any heat. For most commercial installations, a good everyday blade should cost no less than $50 and perhaps even $75 or more. Remember that proper side dressing is critical.
Once the blade is mounted on the arbor, it should be flat. When turned by hand, it should not have any wobble or run-out. Use a micrometer or dial indicator to check this. Run-out can be a problem with the blade or, more likely, a problem with the arbor bearings or the collar flatness.
Avoid heating the blade, because heat can ruin the blade quickly. One cause of heating can be a dull blade. Keep the saw clean. Although not covered here, the setup of the saw machine itself is also important.
Finally, please be careful with a saw. It does not know the difference between wood and fingers. Use all safety devices. Avoid kickback hazards.
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