The circular saw, often called a "skill" saw, after the popular Skil brand, is one of the most versatile of power saws. They are capable of almost any cut that can be made on a table saw, and much more, since their portability allows pieces to be cut in position. The Porter Cable brand is a line of reasonably priced professional quality tools. Their circular saws are constructed similarly to most common brands. Since a sharp blade is essential to the function of your saw, replace, or sharpen your blades regularly.
Unplug the saw from the power cord or outlet to ensure the blade will not accidentally start during the blade changing procedure.
Select a blade for the project you are working on. There are dozens of different styles available. Choose fine tooth blades for delicate material, such as cabinet grade plywood, and coarser teeth for framing lumber and other heavy cutting.
Set the saw firmly on a sturdy work surface and locate the blade stop mechanism. Look for a black button on top of a thin metal rod, just behind the blade guard, on the top of your Porter Cable saw. Depress this button to activate the blade stop and keep it pressed in throughout the removal process.
Pull the blade guard back to expose the blade and fit your wrench to the nut, adjusting as needed for a snug fit. Set the wrench so that there is ample room to move it in a counterclockwise direction. Pull or push the wrench to turn the nut in a counterclockwise direction until it stops turning when it butts up against the blade stop.
Changing the Blade
Apply additional pressure to the wrench to turn the nut hard enough to unlock it. Continue turning the nut in a counterclockwise direction to remove it. Set the nut aside and lift the blade off of the spindle, sliding it out through the slot in the base of the saw.
Fit the new blade through the same slot and over the spindle with the printed side facing out to ensure the teeth are turned the right direction. Fit the blade onto the spindle and turn the nut back onto the spindle, twisting clockwise by hand until it is finger tight.
Depress the blade stop and refit the wrench onto the nut. Turn it until it stops against the blade stop. Apply additional pressure to turn the nut tight to lock the blade onto the saw. Plug the saw in and return it to normal use.