Whether your circular saw has a carbide-toothed or regular blade, at one point or another they all become dull from use. Replacing the blade can be a bit confusing if the arbor on the saw does not correspond to the blade’s mounting hole. Some arbors are a diamond shape, and others are round. Most modern saw blades come standard with a round hole and offer a prefabricated “knockout” to drive out a diamond-shaped slug for the unique arbor hole. By following a basic process, you can replace the circular saw blade in a matter of minutes.
Unplug the saw from all power sources.
Turn the saw blade by hand while depressing the motor shaft arbor lock button. This button is generally located next to the motor and the saw blade safety shield. By pressing this button as you revolve the blade, a pin will fit into the motor shaft, preventing it from turning while using a wrench to remove the arbor bolt.
Place the crescent wrench or saw blade wrench over the arbor bolt and turn in a clockwise direction to loosen and remove the bolt. Most, if not all, circular saw arbors have left-handed threads. This means that to loosen the nuts, you must turn it clockwise.
Pull the saw blade from the arbor shaft after removing the thick metal bushing. Check whether the arbor is a diamond shape or round hole. If the arbor is round, simply place the new blade on the arbor shaft with the cutting teeth facing forward and proceed to Step 7. If the arbor is diamond-shaped, you may have to "knock out" the diamond-shaped slug with a hammer.
To remove the diamond slug, place the new saw blade on a firm wooden surface. Use the side edge of the hammer face and strike the center of the diamond "knock out" slug sharply. The slug should break away cleanly from one accurate hit.
Place the blade on the saw arbor shaft, aligning the diamond knockout with the shape on the arbor.
Slide the heavy bushing over the blade and insert the bolt. Remember that in order to tighten a left-handed thread, you must turn the bolt counterclockwise.
Push the motor shaft arbor lock button again to keep the motor shaft in place while tightening the bolt. Plug the saw into the wall outlet once the blade is securely on the arbor and allow the saw blade to run a few seconds. This will help to balance a thin circular saw blade.