Circular saws come in a variety of power packages. Some saws plug into the wall. Other circular saws are battery-operated. Even larger circular saws are powered by a small gasoline engine. Regardless of the power source, they all cut material using a circular blade.
Direct Drive - The most common type of circular saw uses a direct drive to the electric motor. In these types of saws, the blade is connected to the end of the motor shaft. Whether the blade hole is the high-torque diamond hole or the universal round hole, they all attach directly to the spinning motor shaft.
Double Gear Drive - Some circular saws employ a double round gear to increase the speed of the blade through a lower-rpm motor. The two gears are inter-meshed; one is attached to the electric motor and the other to the blade shaft. The motor gear is larger in size or has more teeth. The blade gear will have fewer teeth on it. When the motor turns, the blade shaft will spin faster than the motor, depending on the ratio. The most common ratio is a 2 to 1. This means that the motor may turn at 1750 rpm and the blade will spin at 3500 rpm. These types of saws have a high blade speed but lower torque. They are good for cutting thin material such as paneling and plywood.
The Worm Gear - A long-lasting and strong circular saw is the worm gear type. This saw uses a gear that changes the motion of the motor at a right angle. The advantage to this type of saw is the amount of torque delivered to the blade. Generally, the worm gear saw is used for cutting thick framing materials. Gear reduction in speed is also achieved in the gearbox. The electric motor may spin as fast as 3500 rpm, but through the gear reduction, the blade is slowed to 1750 rpm. This gives a high torque to the blade so it can muscle through thick cuts.
The Blade - The design and construction of the circular saw blade is the key to cutting through any material. Regardless of the type of saw, if the blade is not sharp or the correct type, it just will not do the job. The more teeth on the blade, the more cuts per revolution you will have and the cleaner the cut. Carbide teeth provide a long-lasting blade. These type of blades will last for years if you prevent them from hitting metal. If you hit a nail, the carbide will cut through it, as compared to a regular steel blade that will dull quickly. The designs of the individual teeth on the blades are made to cut and remove the sawdust with each pass of the tooth. As the saw is advanced through the material, each tooth removes a small amount of material to make a complete cut.