A hole saw is a circular saw that can be attached to a drill to cut holes in thin pieces of material. Hole saws are often also referred to as hole cutters and consist of sharpened saw teeth moulded around the edges of a cylindrical plate which is mounted on an arbour that can contain a drill bit, which is attached to the drill.
Adjustable hole saws have cylindrical plates covered with a series of grooves in circles around the drill bit, each with a different radius, into which a saw can be fitted to make it possible to cut different sized holes.
A circle cutter is another type of adjustable hole saw that has two or three adjustable teeth on a cylindrical platform. The teeth can be adjusted to a specific radius to cut a hole of that size.
Most hole saws will work with standard drills, but most cordless drills won't have enough power to sufficiently operate one. Hole saws are relatively inexpensive and they can be used to cut through wood, plastic, soft plaster and metal. Diamond hole saws that can bore holes in brick, concrete, glass and stone are also available.
The kerf 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 and sloping slots in the cylinder will help carry saw dust out. It takes some skill and a bit of practice to cut a hole without ragged edges using a hole saw, but the trick is to cut from both sides of the material if possible. It might be difficult to keep the hole straight if you drill from both sides, which is why you should use a longer drill bit in the arbour. The drill bit will drill a hole which serves as a centre guide for when you switch over to the other side. Place the drill bit in the same hole and make sure that the saw teeth are evenly contracted with the material before you start to drill.
Hole saws come in a variety of sizes and can often cut holes up to a foot in diameter. Hole saws are very efficient, because very little of the material removed is actually being cut, which reduces the overall power requirement.