Q I’ve got some internal remodelling to do that entails drilling large holes in the studs and joists of drywalling. What works better, a hole saw or one of those big drill bits that contractors use? I have a 12 mm drill. Will that do the trick, or should I rent a larger one?
A When plumbers and electricians need to drill a large hole in framing timber or other material – to make way for pipes and wiring – they usually opt for a self-feed bit (see image). Such bits max out at a diameter of about 10 cm. Another choice for the pros is the auger bit, which can drill holes about half that size. Hole saws present a third option, though they can be problematic, which I address below.
The last part of your question tells me that you understand an important, basic fact about using these bits: it takes a big drill with lots of torque to spin them. Contractors use specialised tools with the chuck at a right angle to the motor. The 90-degree design allows what is known as a joist drill, or a stud-and-joist drill, to fit between wall studs and floor joists while driving the stubby self-feed bit. More advanced versions of these drills have a clutch that prevents them from breaking your arm if the bit grinds to a halt and the torque transfers to the handle.
So, can a standard 12 mm drill power a self-feed bit? Maybe. Y our drill will certainly get a workout – and you may risk frying the motor – if you use a bit larger than 50 mm. Any bit bigger than that probably dictates that you rent a more powerful drill; ditto if you’re going to be cutting a lot of holes. Even so, this type of drilling is tough work. Take your time, and be sure to use a heavy-duty extension cord.
That brings us to hole saws. Certainly one of these bits can bore through framing timber, especially when chucked into a 12 mm drill. But hole saws have some drawbacks. Their shape and cutting action don’t eject chips and sawdust, so you repeatedly have to back out the saw to clear debris. That makes a hole saw slower in thick material than a self-feed bit. You also need to pry out the plug of wood that the saw creates. Better-quality hole saws have stepped slots in their body to make removing the plug easier.
Be sure to gauge the size and position of any hole you drill so that it doesn’t damage the framing timber. The International Residential Code allows a hole that’s up to 40 per cent of the width of a stud in load-bearing walls or 60 per cent in non-bearing walls. (That translates to holes of 35 mm or 28 mm.) In either case, the hole should not be closer than 16 mm to the timber’s edge.
Those are the basics. For a more detailed take on the topic, there’s plenty of good advice online.