Hole saws are a go-to tool for drilling large-diameter holes on the job. Keep this information in mind.
Whenever you need to drill large-diameter holes quickly and cleanly, a hole saw is oftentimes the best solution. But unlike traditional drill bits, hole saws can be tricky to use. Here are six tips and techniques for getting the most out of your hole saws.
- Enlarging Existing Holes
Hole saws are guided into and through the workpiece by a center pilot bit. However, the pilot bit is rendered useless when trying to enlarge an existing hole because the bit has nothing to drill into. Here’s how to remedy that: Start by marking horizontal and vertical lines to represent the exact center of the existing hole. Next, clamp a scrap piece of plywood over the existing hole. Then, transfer the centerlines of the hole onto the plywood. Now place the hole saw’s pilot bit on the intersection of the two centerlines and drill through the plywood and workpiece.
Another way to enlarge an existing hole is to mount two hole saws onto the arbor — one inside the other. The smaller, inner hole saw must be the same diameter as the existing hole. The larger, outer saw should be the same size as the new, enlarged hole. As you begin to drill, the inner hole saw will slide through the old hole and help guide the larger hole saw through the cut. Note that not all arbors will accept two hole saws.
- Preventing Blow Out
When a hole saw exits the cut, it tends to blow out the back of the workpiece, leaving behind a ragged, splintered surface. That’s not a concern when blasting holes through floor joists or wall studs, but it is when sawing through more-finished surfaces, such as a door. Here are two ways to avoid blow out: Clamp a scrap board to the back of the workpiece and drill into that; drill halfway through from one side and then finish the hole by drilling through from the opposite side.
- Metal Drilling
Hole saws are equally adept at drilling through metal as they are at boring through wood. Whenever possible, use cutting oil to lubricate the hole saw when drilling metal. The oil serves two important purposes: First, it reduces friction, which keeps the hole saw cooler so it cuts better and lasts longer. Second, cutting oil helps flush metal chips out of the kerf, allowing the saw teeth to do their job.
You could simply squeeze some oil onto the metal, but try this trick instead: Place an ordinary kitchen sponge between two pieces of scrap plywood. Use the hole saw to drill through the sponge sandwich. Remove the circular plug of sponge from between the plywood and stuff it into the hole saw. Saturate the sponge with cutting oil, and you’ve got a self-lubricating hole saw. There’s one exception to this rule: Cast iron is always drilled dry; don’t use any sort of lubrication.
- Stress-Relief Drilling
Drilling large-diameter holes can be demanding and stressful, especially on your wrists, the drill motor, and the hole saw. To make tough hole-sawing jobs a bit easier, try drilling a series of stress-relief holes around the perimeter of the cut. Start by using the hole saw to cut a 1/8-inch-deep circular groove into the workpiece. Next, switch to a 3/16-inch-diameter drill bit and bore a series of closely spaced holes around the perimeter of the circular groove. Now go back to the hole saw and finish drilling out the hole. What you’ll find is that the 3/16-inch-diameter relief holes allow the hole saw to cut much more quickly with reduced stress and strain.
- Plug-Removal Tips
One of the top complaints people have about hole saws is extracting the wood plug from inside the hole saw after drilling each hole. There are plug-ejecting hole saws, but they’re not very common and only available in limited sizes.
The most common way to remove the plug is to simply pry it out with a slotted screwdriver, which works OK but is extremely tedious when drilling many holes. Try this instead: Drill halfway in from each side of the workpiece, which leaves the plug protruding from the hole saw. Then simply grab the plug and yank it out of the hole saw.
If you can’t drill in from each side, and the plug can’t easily be pried out, bore two pilot holes through the wood plug on each side of the hole saw’s pilot bit. Then use a cordless drill to drive a 3-inch screw into each hole. Alternately, drive each screw in a little at a time. When the screws bottom out against the inside of the hole saw, they’ll push out the plug.
- Sawing Tough Material
To bore holes through tile, cement backerboard, fiber-cement board and other tough, abrasive materials, use a hole saw that is rimmed with super-sharp carbide or diamond grits. These hole saws cost more than traditional bi-metal hole saws, but they cut smoother and last much longer.
About the Author
Joseph Truini is a home improvement expert who writes about home remodeling and repair, woodworking projects, and tools and techniques for homeowners and professionals. He has authored six books and his work has appeared in several national magazines. Truini also writes for The Home Depot, which carries a wide selection of hole saws.