Hole saws are cutting tools used to make circular holes in a variety of materials. Also referred to as a hole cutter, the tool consists of a cup-shaped metal cylinder with a toothed cutting edge on the open end, usually accompanied with a drill bit to center the hole and keep the saw teeth from slipping. The maximum depth of the hole created is determined by the length of the hole saw body.
The advantage of hole saws is that they create holes without needing to cut up the core material. This is especially preferable to twist drills or spade drills for relatively large holes (larger than 1 inch). They are also less expensive than boring bits. Disadvantages include the need for a drill that is capable of producing considerable torque at low speed, the tendency to bind if choked with dust, and the core plug can become lodged inside the hole saw.
The saw consists of a metal cylinder, usually steel, mounted on an arbor. The cutting edge either has saw teeth formed in it or industrial diamonds embedded on the teeth. The arbor, also called a mandrel, is responsible for connecting the drill bit to bore and holding the pilot bit. The sloping slots in the cylinder wall help carry the dust out. The kerf (defined as the distance between diverging saw teeth) of the cut is designed to be slightly larger than the diameter of the rest of the hole saw so that it does not get jammed in the hole.
Most hole saws have solid cylindrical shapes and are designed to cut a specific hole diameter.
There are two types of adjustable hole saws, adjustable hole and circle cutters:
Adjustable hole saws can make holes of different sizes. It has a flat metal disc with a series of grooves that make progressively wider circles. The saw teeth can be snapped into the grooves that correspond to the size of the planned hole.
Circle cutters are also adjustable. They have two or three teeth on a platform with a pilot bit. To cut out a hole of any size they need to be adjusted to the proper position. Circle cutters can make larger circles than adjustable hole saws.
Saw teeth are used for most materials, such as wood, plastic, soft plaster, and metal. Diamond hole saws bore holes in brick, concrete, glass, and stone. Very hard materials should be drilled with water; otherwise excessive heat generated during the drilling process can damage the saw material.