Choosing the right tool for the job at hand is one of the most important aspects of woodworking. You wouldn’t use a chisel to drive a woodscrew, nor would you put a drill bit into a router and try to bore holes. So whywould anyone want to rip lumber with a crosscut blade? In the next few articles, I’ll be discussing the choices to be made when considering circular saw blades.
Why Pay for Carbide?
The original blade that comes with most saws is usually a plain, ordinary steel combination blade. Chances are it’s not only plain and ordinary but, if it has been used for any length of time at all, is probably outright dull. Hardened steel blades require frequent sharpening-so much, in fact, that this can lead to frequent replacement. Instead of replacing the saw with a similar blade, however, the serious woodworker would do better to invest in a set of carbide-tipped blades.
Carbide blades not only stay sharp longer, they cut through hardwoods with less effort on the part of both operator and machine. What’s more, the wood is left with a clean, smooth edge, usually ready for gluing.
It’s the tooth itself that is responsible for these miracles. More than just a serrated disc, these blades have individual teeth made of tungsten carbide, an allow made from carbon and tungsten and bonded with cobalt, which is one of the most durable substances made by man. When these teeth are brazed onto a hardened steel saw body, the result is the most durable blade possible.
More Than One Blade
Unless nothing is cut but particleboard, the well-equipped shop is going to need several different blades for different purposes. There are excellent carbide-tipped combination blades available, and they can be very useful. Along with being fine for cutting many of the softer woods, they are perfect for plywood. (After all, because of the criss-cross grain pattern, any cut made in plywood is a combination of ripping and crosscutting.)
Unfortunately, combination blades are not ideal for every cutting task in the shop. For the best results in ripping or crosscutting hardwoods, it is better to have separate blades which are made for these specific applications.
Differences in Design
To understand why some blades perform specific tasks better than others, certain factors of blade design must be considered. The most important aspects are the gullets and the hook angles.
Gullets are the curved valleys that follow each tooth, acting like a scopp to clean chips and sawdust from the cut. The hook angle, or rake of the tooth, is the angle between the face of the tooth and the center line of the blade. A larger hook angle means the tooth is taking a bigger bite, than a larger gullet is needed to clear the sawdust.
Because of their very slight hook angles (usually no more than 10 degrees), crosscut blades have small gullets. And since gullets do not consume much of the space around the blade’s circumference, it is possible to have up to 60 and even 80 teeth on a 10″ blade. These teeth are usually ground with either an alternate top bevel or hollow ground with inverted “V” teeth. The smaller bites taken by each one are what allow the blade to cut across the grain without tearing.
With a hook angle of 20 to 30 degrees, and the larger gullets which that entails, rip blades are able to cut material at a faster rate of speed. They usually have about 24 teeth with a square top grind for faster chip removal.
In most cases, combination blades have around 40 teeth. Their alternate top bevel teeth have a small hook angle for about 15 degrees to prevent tearing when crosscutting. Every fifth tooth is usually a square top “raker” with a large gullet in front to assist in ripping. Clearly, there is some compromise involved in the quality of both operations but, in certain cases, this may be acceptable.