A circular saw is the tool of choice for making straight, square cuts. Circular saws can cut metal if they are properly equipped, but they are most commonly used to cut wood and engineered-wood products such as plywood and Oriented Strand Board (OSB). The base of a circular saw provides a straight edge to facilitate accurate cuts, and the circular shape of the blade helps to keep the cut edge perpendicular to the surface of the wood. Typical uses of a circular saw can be grouped into crosscutting and rip cutting.
Instructions Crosscuts - Use crosscuts when you need to make a perpendicular cut across a length of wood. This usually means cutting a piece of dimensional lumber across its width. Measure and mark your cut with a pencil.
Press the larger edge of your square up against the edge of the wood and move the square until the other edge lies on your pencil mark.
Draw a line along the edge of the square to ensure that the cut line is perpendicular to the wood edge.
Align your circular saw so the pencil line is in the notch at the front of your saw's base. Consult your instruction manual to determine where exactly to place the notch for your particular saw model.
Start your saw and let it come up to full speed, then carefully push the saw through the wood, keeping the pencil line in the notch.
Rip Cuts - Use a rip cut to saw along the length of the wood. This usually means cutting a piece of lumber through its longer dimension, such as sawing a 2-by-4 into two 2-by-2s.
Measure an equal distance from the edge of the wood at both the beginning and end of your rip cut.
Connect these measurements with a line to provide a guide for your cut.
Make your cut by following the line, just as with a crosscut.
Use a rip guide if you cannot make your cut sufficiently straight by manually following the line. A rip guide attaches to your saw and extends an adjustable distance from the saw base. A flat surface on the end of the rip guide allows you to make very accurate cuts by keeping the flat surface pressed up against the edge of the wood.