Making large-diameter mortises for chairs or staked tables requires big drill bits and a way to drive them. Usually a drill press won’t work because the workpiece is too large and the angles are too odd. So here are some bits that work – and some to avoid.
To drive big bits (1-1/4” and bigger), you probably need a corded drill. I’ve tried using a brace, but that’s a tall order in hard woods. Battery drills, for the most part, aren’t up to the task either. I prefer a corded drill with a traditional keyed 1/2” chuck.
The type of bit is also important. My favorite kind is what gets labeled a “ship’s auger,” shown in the photo above. This has a lead screw that is long enough that you can tilt the bit for compound angles (the lead on a normal Forstner is too short for anything but shallow angles). The solid body of the auger keeps your bit on track with little chance for wandering. The downside is these bits are your most expensive option – an 1-1/4” ship’s auger is about $25 at my hardware store. Another brand I’ve had great luck with is WoodOwl.
A similar option is the shorter auger shown above. It’s about half the price of the ship’s auger. Its downsides are that its spurs along the rim are fairly short and ineffective. So the entry hole is gonna get a little torn up. Also, it’s short. So it will wander in holes deeper than 2”.
The third type of bit that I like is a spade bit with a lead screw. The lead screw makes the bit fairly aggressive and reduces its tendency to wander. These bits are usually about $6 and work surprisingly well.
What doesn’t work well for accurate mortises is the traditional spade bit with a traditional tip (i.e. no lead screw). This bit jumps around and rattles too much for accurate work. It is the cheapest of the bunch, but also the least useful.
Or maybe this bit is the least useful. Sometimes called a “cup” bit, I decided to give it a go. The long drill bit in the center allows you to tilt the bit to almost any chairmaking angle. But the outer cutting rim is a joke. It clogs immediately because there’s no place for shavings to go. So you have to pull the bit out every 1/8” and clean out its gullets.
Note that these recommendations are for large-diameter bits. For smaller-diameter holes, an auger and a brace are my preference.
— Christopher Schwarz