Hole saw basics
Spade bits are the tool of choice for drilling holes up to about 1-1/4 in. in diameter for running electrical wiring and other uses. But when it comes to drilling really big holes for locksets or plumbing pipes, reach for a hole saw. A hole saw is a steel cylinder with saw teeth cut into the top edge. Hole saws don't cut as quickly as large boring bits driven by a pro's powerful 1/2-in. drill. But boring bits are expensive ($30 plus drill rental). Hole saws, on the other hand, are readily available at hardware stores and home centers for as little as $5 and work with a standard 3/8-in. drill. Cutting clean holes with hole saws requires a little skill and practice. Here are the key techniques that will make the task safer and give you the best results.
Proper setup is important
Mount the correct-size hole saw in the arbor. If your hole saw has an adjustable center bit, make sure it protrudes past the toothed edge of the saw about 3/8 in. (Photo 2). If the center bit has a flat spot on its shank, align this with the setscrew. Then tighten the setscrew to secure the bit. Finally, tighten the hole saw in the chuck of a corded 3/8-in. variable speed drill. Cordless drills won't have enough power unless they're 18 volts or larger.
Start slowly and hold on tight
Photos 1 - 4 show how to drill a hole in a wood door for a lock or door handle, but the same techniques apply for drilling other holes. When you need a clean, splinter-free hole, drill in from both sides (Photos 1 and 4). The key to getting a perfectly straight hole is to ensure even contact at the start. That will put your drill at a right angle to the door (Photo 3).
A hole saw is a steel cylinder with saw teeth cut into
the top edge.
Buying Hole Saws
For as little as $15, you can buy a set of carbon-steel hole saws for drilling wood. For about $45, you can buy a set of bimetal hole saws that will cut wood and metal and last a lot longer. You can also buy specialty hole saws coated with Carborundum or diamond grit to cut hard materials like tile and stone. These saws, however, won't cut wood. Most hole saws mount to a separate centering guide called an arbor. Others are one piece. Better arbors (about $12) have two pins that slide into holes in the bottom of the hole saw to lock the saw in place. Match the arbor to your saw and check that it will fit in your drill. Some arbors require a 1/2-in. chuck and drill.
Most locks and door latch sets require a 2-1/8-in. hole, so if you buy a set of hole saws, make sure it contains this size.
Enlarge existing holes
There's just one problem when you need to enlarge an existing hole. The center bit on your hole saw must be engaged in wood before you can start a hole; otherwise, the saw will just spin and gnaw its way across the surface, leaving a mess behind. Clamping a 1/4-in. piece of plywood over the existing hole is the easiest solution (Photos 5 and 6). Another method is to jam a wood plug into the existing hole.
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Chisel out the core for deep holes
You can drill deep holes with a hole saw if you chisel out the wood plug as you go (Photo 8). This is useful when you only have access to one side of thick material and your hole saw isn't long enough to go all the way through. If you don't have a chisel handy, break out the plug with a standard screwdriver.
Hole saws are surprisingly hazardous
Tilting the drill or hitting a nail with the hole saw while you're drilling can cause the saw to bind and the drill motor to twist violently in your hands. The powerful torque can slam the drill into your face or strain your wrist. Since binding is hard to predict, your best defense is to brace the drill handle against your hip or leg if possible and maintain a firm, two handed grip. If your drill has a side handle (Photo 7), use it.
In addition, take the following precautions for safe hole cutting:
- Keep the drill going straight to avoid binding the hole saw.
- Don't wear loose clothing or jewelry that could become entangled in the hole saw.
- Locate the trigger speed lock-on button (if your drill has one) and avoid pressing it as you’re drilling. (I like to disable these locks by filing or sawing off the button so it's flush to the handle.)
- Clamp loose projects or small pieces securely with at least two clamps to keep them from spinning.