Cut through a two-by-six or a piece of plywood with a hand saw, and there's likely to be not just a lot of huffing and puffing, but a meandering line as well. Yet switch on a circular saw, and the cut will come out straight and easy.

Circular saws are the workhorses of any construction job, from framing an addition to building a tree house. They glide through lumber in seconds, and can be fitted with an assortment of blades that rip through everything from nail-embedded wood to concrete blocks and bricks.

The saws come in a variety of sizes, but the most popular contains a blade 7.5 inches in diameter. The blade on most models can be adjusted to cut on a bevel up to 45 degrees, which is useful in cutting boards to frame the pitch of a roof. Larger jobs, such as cutting the timbers used for post-and-beam construction, require saws with blades of at least 12 inches in diameter. Correspondingly, lighter saws with reduced blade circumference should be used for smaller projects such as cutting plywood or two-by-fours. Regardless of the size of the blade, circular saws come in two varieties.

Worm-Drive Saws

A worm-drive saw is the toughest, most powerful circular saw, making it the right choice for heavy-duty jobs like framing an entire house or sawing through concrete. The saw derives its name from a pair of gears--the worm and the work gears--that position the motor shaft and the blade at right angles to each other. This gives the tool its characteristically broad shape.

The worm-drive saw also contains an oil-filled reservoir, similar to a crankcase, that lubricates the two gears and dulls the circular saw's ear-splitting scream. In addition, the blade's position on the left side of the motor makes it easy to see and follow the cutting line as you're working. Because of its power this saw is noticeably heavier than other models; the weight may add to fatigue if it's used for any length of time.

Sidewinders

Because of their lightweight portability, sidewinders are the most popular model of circular saw--ideal for anyone doing less than major construction jobs. The blade and the motor are aligned alongside each other, for a compact profile. The disadvantage to this configuration, however, lies in a slight difficulty in being able to see the cut while you're using the saw. In order to get a clear view you must lean over the saw, which can become tiring after long periods of use.

Blades

Without a good blade, a circular saw is about as useful as a hand saw. Less expensive blades are made from steel, but stronger and more durable ones are cast from carbide. Regardless of the material, the key to proper use lies in choosing the right blade for the job, and sending it to a tool shop for occasional sharpening. See all circular saw blades.

• General-purpose blades contain about 20 teeth, and balance speed with durability to create smooth cuts.
• Fine work such as cutting window trim or crown moldings requires a blade with more teeth--between 40 to 60--for a smoother cut.
• Veneered plywood used for cabinets or paneling should be cut with a plywood blade made up of a mass of tiny teeth like those on a hand saw. These blades cut slowly without splintering.
• Heavy-duty work requires different blades altogether. A remodeling blade with about a dozen square-edged teeth can rip through wood hammered with nails. And for cutting stone or concrete, choose a masonry blade. Rather than teeth, this blade has an abrasive edge that literally grinds through material.

Cutting Tips

Circular saws are designed to make straight cuts rather than curves or angles. Forcing the saw off a line will cause the blade to bind, which could make the whole saw kick backward--a dangerous situation. For the same reason, make sure that blades are clean of resinous gum from wood before using them. These sticky deposits could also cause the blade to bind, resulting in kick back

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