Teeth Number

Other than abrasive blades, such as used for cutting ferrous metals, glass and tile, all saw blades have a number of teeth interspersed around their circumference. The number of teeth on the blade is one of the most telling characteristics about that blade’s intended purpose and one of the biggest considerations when choosing a blade. Generally, it’s the first parameter you should take into account when buying a saw blade. The quantity will describe is it designed for ripping or crosscutting, for wood or for masonry, for thick or thin materials. There are two extreme types: a blade with fewer but larger teeth with greater spacing between each used for rip cuts, and blade with numerous small teeth made for crosscuts.

Teeth on Crosscut and Rip Saw Blades

Circular saw blades which are designed for rip cutting generally have a smaller number of teeth. They are designed to take a larger wood chip or “bite” out of the wood, cutting through it faster. As ripping is easier than crosscutting, having a blade that can take cut a larger chip increases efficiency, without sacrificing the quality of the cut. To accommodate this rapid cutting, rip sawing blades will have less than 40, down to 18 teeth, with large gullets between, depending upon the size and quality of the blade. On the other hand, when blades are used for crosscutting, they need to cut through the grain of the wood, making them take smaller bites and produce smaller chips. This requires a larger number of teeth, without large gullets. Crosscutting blades have from 80 to 150 teeth. The more teeth the blade has, the smoother the cut will be. Hollow ground or plywood saw blades have approximately the same number of teeth, but beware; properties of these blades are significantly different from those considered as combination/multipurpose blades.

Teeth on Combination Saw Blades

Combination blades fall in between these two numbers, ranging from 40 to 80 teeth. These blades are a compromise, intended to allow the same blade to be used for both ripping and crosscutting. As such, they are not the best at either, although they do an adequate job of both.

Selecting a Saw Blade by Teeth Number

For most woodworkers, the number of teeth a blade has is the most important part in selecting a blade. Generally speaking, a higher tooth count is an indication of a higher quality blade, as each tooth added to the blade increases the blade’s cost. This is especially true of carbide-tipped saw blades. However, just the number of teeth isn’t enough.

Appropriate Number of Teeth

The best way to find out which saw blade matches your need is to cut an inch of material, let’s say we are dealing with lumber. Now, when the saw blade is in a pre-cut slot and the circular saw is turned off, some of teeth cannot be seen if watching from a side. If three teeth are in the slot, that’s very good, the blade is very likely good for a job. Moreover, 2 and 4 teeth are still good, but less or more probably won’t do the cutting very well. If you choose less, the finish won’t be neat as expected, but choosing more than it’s suggested will bring the risk of overheating and slow down the cutting process.
Imagine the cut circle of a table saw for a moment. When properly adjusted, the saw blade will only protrude above the material being cut 1/8” to 1/4”. As the top of the blade turns towards you during the cut, the first part of the revolution, the saw tooth is only passing through the kerf in the wood. It isn’t done until it goes “over the top” and starts coming back down through the wood that it is cutting. That’s the part where you have to count the teeth. The same concept works with a radial arm saw. As the blade rotates, it is rotating with the top towards you. When the tooth enters the wood, it is traveling in the kerf. Once it passes below the wood and then starts coming back up through the wood, it starts cutting.
While having three cutting teeth is considered ideal, less teeth are possible, if you are willing to sacrifice smoothness of cut. In no way should you ever have less than one tooth per thickness of your material as there is a good chance that it will hang up on the wood, stalling the saw. More teeth than the “three-tooth” recommendation will help make the cut all that much smoother, but at the cost of creating additional heat. Therefore, it is important when using a blade with a high tooth count that you allow the blade ample opportunity to cool between cuts.

Teeth per Inch

Processing thick materials may require large diameters, bringing the fact that the total number of teeth must be compared with the diameter of the circular blade. Besides the total teeth number, a much better measure to use is the number of teeth per inch of circumference length (or diameter, even simply). Although it is not normally labeled on the blade’s packaging, it’s an important factor for selecting a blade to go with a material. The blade with more teeth per inch of the circumference of the saw blade is good for thicker materials, while the one with fewer number of teeth is recommended for thinner ones. Perhaps it would be easier to think of this, if we imagine a band saw blade. On the band saw, one can put their stock to be cut against the blade and count the number of teeth that will be passing through the material at one time. Normally, a minimum of three teeth is considered acceptable. On harder materials, more teeth may be used. The reason for this is wearing of the teeth when cutting thick and heavy materials, especially if finish quality is important. This translates directly to circular saw blades, precisely crosscutting blades. For a smooth finish, a minimum of three cutting teeth should be in the material at any one time. However, not all the teeth that are within the material thickness are cutting. For both table saws and radial arm saws, the teeth of the blade are only cutting during the second part of the ark through the wood.

Diameter and Teeth

Remember, the diameter of the blade has a factor here. For the same types of cut, teeth number is proportional to the diameter, and to keep this ratio larger diameter means more teeth. An eight inch circular saw blade with 40 teeth and a 12 inch saw blade with 72 teeth will have the same number of teeth per inch, due to the larger circumference of the 12 inch blade. At one inch of diameter length there are usually from 2 up to 20 teeth, approximately about 4-8 pieces. Blades averaging the middle are labeled as combination blades, acceptable for rip and cross cuts. In case the number is lower, blade’s original purpose is quick ripping that leaves rough cut, requiring sanding to achieve a tidy finish. However, buying a product with more teeth will create a smoother finish with a cost of cutting speed. Of course, this all depends on the type of material you are working with, and overall feed rate.

Cutting Fast or Slow

The harder the material you are cutting, the slower the cut should be. There’s always an option to choose between the time needed to do the job and a clean-cut. Since some types of saws don’t have speed controls, one way of reducing cut speed is to use a blade with less teeth, in case the requirements of finish aren’t important. This will help prevent overheating. Remember, using rip blade for cross-cuts will tear the wood fibers at the ends. Using predetermined crosscut as a rip blade will make much sawdust and cause overheating due to of shallow gullets and dense teeth configuration.
As a conclusion, for occasional use and non-professional woodworkers it’s smarter to buy a combination saw blade than using specialized blade for other kinds of cuts. Teeth number should accompany the dimensions, material and cutting type. You can buy a saw blade with more or less teeth, but the diameter should follow the proportions. Remember that circular saw also has limitations when the diameter of a circular blade comes along. In addition, when cutting non-ferrous metals, a small amount of cutting oil should be applied along the cut line, in order to lubricate the blade to material interface.