Blade’s anatomy

How blade components work together to make productive cuts

by Paul Markgraff

Though they appear to be simple tools, more than a dozen components on a circular saw blade work together to create the conditions for cutting.

Each aspect, from the manufacturing process to the type of cutting edge to the width of the blade, impacts the performance of the blade. Contractors that understand how each part works stand a much higher chance of purchasing the right blade for the job.

“All saw blades are basically made up of the same parts,” says Brad McMullen, product manager, saw blades for DeWalt. “The differences are the quality of the blade, the quality of the cut and the application the user is looking for.”

Making the cut
Suppliers manufacture the basic component of circular saw blades – the body – with different methods. Small, thin blades are generally stamped from a sheet of metal. Some of the larger, thicker blades are cut from metal sheets using a laser. Opinions vary on whether either method eliminates blade wobble or warping.

Stamping is generally used for thinner blades produced in higher volumes, while laser-cutting is used for thicker, lower volume blades.

“There is no difference in performance,” says Adrian Liechti, saw blade product manager for Bosch Accessories. “The major problem for wobble or imbalance is the steel body. Even if you laser-cut, you have to surface-grind it and use other methods to keep the blade flat.”

Blade bits and pieces
A circular saw blade is a conglomerate of parts machined to precise specs. By adjusting the different parts of a blade – the kerf, the blade width, the type of tip, the finish and so forth – contractors can get the right tool for the job.

Kerf
Simplified, the kerf is the width between the left striking edge of a blade tip and the right edge of a blade tip. The kerf is actually wider than the body of the blade, allowing the slicing edge to move faster through the cutting material. The width of a cut through any material is the width of the kerf.

The main difference between thinner and thicker kerfs is speed: the thinner a kerf, the less material it is removing, and the faster the blade cuts.

Heat expansion slots
When circular saw blades slice through material, they create friction, which creates heat. As the blade heats up, molecules within the blade expand and the blade expands with it. Heat expansion slots prevent the blade from warping by distributing heat evenly.

Many circular saw blades contain three to six heat expansion slots at even intervals around the outside of the blade. They are the vertical cuts between blade teeth that end in a semicircle or circular cutout.

Body slots
In the body of the circular saw blade, manufacturers cut out symmetrical body slots. In most cases, manufacturers say these slots encourage blade cooling. They can be diamond- or wedge-shaped.

On many 10" and 12" table saw and miter saw blades, manufacturers will laser cut a W-shape into the body of the saw blade. These body slots reduce noise by more than half and reduce blade vibration while in use. Though these slots serve a definite purpose, they also decrease the stiffness of the blade.

Blade coatings
There are several different coatings that manufacturers may apply to circular saw blades for various purposes. Most blades get a water-based dip coat, which helps prevent rust. Some blades have anti-friction coatings baked into the blade. These coatings help the blade slide through material without excess heat buildup. Teflon-coated blades clean up easier and use less energy than non-Teflon-coated blades. Titanium coatings prevent corrosion and extend tool life. All coatings offer one major benefit: they improve the speed of the cut.

Tooth count
Contractors can follow one simple rule when it comes to blade speed: the more teeth, the slower and cleaner the cut. Framers who need to cut hundreds of studs a day will get the best performance out of a 7 1/4", 24-tooth saw blade. Its low number of teeth slice through lumber like butter, but the material is often torn and splintered. Fortunately, this does not matter because the framer’s work is hidden.

On the other hand, woodworkers who need a cleaner and truer cut with very little splintering will want more teeth. Some 10" and 12" woodworking blades can contain as many as 100 teeth. The cut will be slower because of the higher tooth count, but very little splintering will occur.

Another limiting factor is cost. When cutting fibrous cement board, contractors will use a blade with diamond tips. The tips can last up to 100 times longer than carbide tips when cutting this material. However, diamond tips are not cheap. Many blades meant for cutting fibrous cement will have as few as four or six teeth on the entire blade.

Blade width
Among circular saw blades, there are three basic thicknesses. Blades used by contractors are generally thin-kerf blades. They cut quickly and last a long time.

Industrial/woodworking blades are usually thicker than thin-kerf blades and are used to cut hardwood and other materials with precision. For these blades, warping, stability and heat are major concerns.

Economy carbide blades measure somewhere between thick- and thin-kerf blades. These blades are inexpensive and can be used then thrown away.

Hook angle
The angle of the blade face measures the hook angle of the blade. On construction blades, hook angles lie somewhere between +13 degrees and +20 degrees. More aggressive hook angles make a rougher cut, while lower hook angles create a cleaner cut with less blow-out.

On metal-cutting blades, the hook angle is zero or negative degrees, which creates a shearing action instead of a cutting action.

Shoulder
The shoulder on a circular saw blade lies directly behind the blade tip. Shoulders perform different functions, including keeping the operator safe.

Circular saw blades travel at extremely high speeds, and if an operator pushes too aggressively on a circular saw blade, it can become lodged in the medium, creating a kickback situation. The recoil from the blade abruptly stopping can bounce the saw into the air, and the operator can be injured. Slight changes to the shoulder reduce the chance of a kickback.

Carbide grades
One of the most important parts of a carbide circular saw blade is the carbide tip. Several grades of carbide exist, ranging from C1 to C4. 

The highest grade, C4, is the sharpest, longest lasting and offers the cleanest cut. While it offers the best performance in hardwood and fine cutting applications, C4 can chip easily, especially in instances such as striking a hidden nail.

Conversely, C1 is the softest grade, but dulls easily. Highly resistant to chipping, C1 carbide is great for demolition or rough cutting work. Most manufacturers offer a broad range of blades with varying grades of carbide for specific applications.

Working together
All these parts of the circular saw blade work together to perform a single function: cutting material. Variations in saw blade components produce different results, so contractors need to be aware of each dimension of the saw blade to match the right blade to the job.

“When a contractor buys a blade, he can choose the right one for his application,” says Shaun Horan, group manager of accessory product management for Milwaukee Electric Tool Corp. “Knowledge makes a contractor a better buyer and you can find what you need.”

Published in the September 2005 issue of Contractor Tools and Supplies magazine.

back to top