One of the most common questions I get is why I don’t use Forstner bits much in chairmaking. The bits are readily available, make flat-bottomed holes and cut cleanly.
The answer is basically this: The Forstner’s lead point is too short*. That means if I want to drill anything other than a shallow angle I need to start the bit nearly vertical then tilt my drill to get to the desired angle. It’s do-able, but it’s easy to over- or under-shoot things.
So most of the bits I use in chairmaking have a long lead point. This long lead point allows me to tilt the bit to the right angle, lock my elbows then drill. Here are the three bits I use the most, with their advantages and disadvantages.
Star-M F-Type Bit, 16mm, by WoodOwl
This is my favorite bit, but good luck finding it. Most reliable sources are regularly sold out. This bit can handle just about any common chairmaking angle. I can tilt up to 30° off vertical if I make a small starter divot with an awl for the bit’s point.
Other advantages: It cuts clean holes without any splintering on the exit side. This makes drilling through the arm and seat a quick and painless operation.
Disadvantages: The side flutes are sharp. So if you move your drill sideways while boring, you will end up with an overly oval hole. The solution is to practice (sanding down the flutes doesn’t seem to help much).
The bit is metric and drills a 0.629”-diameter hole. So you’ll need to adjust your tenon-cutter to get a snug fit.
Finally, the bit seems to dull faster than my other WoodOwl bits. This is a problem with the other two bits discussed below. I get about five chairs out of one of these bits, and I haven’t found a way to sharpen them (yet).
WoodOwl OverDrive Bit, 5/8”
This bit is much easier to find than the Star-M. So keep searching. Lots of little suppliers have them in stock. The bit makes a true 5/8” hole (0.625”). And it also leaves a clean exit hole.
So what’s the catch? The lead tip isn’t long, so you are limited in the chair angles you can bore. I can easily bore 11° off vertical. And 14° when I am pushing things (and if I make a small starter divot with an awl for the bit’s point). That range of angles will get you through most dining chairs without too much trouble.
Like the Star-M’s, the side flutes are sharp – so practice makes round. And the bit doesn’t last as long as its big auger cousins from WoodOwl, which seem to last forever.
WoodOwl 5/8” Spade Bit
Really, any spade bit will do. The WoodOwl just happens to come sharper than most cheap bits. Another good option is to look for vintage (meaning ye olde 2020) Irwin bits that have the rim cutters. Other people have had luck with Milwaukee and Makita bits. Basically, look for spades that look like the WoodOwls. The bit needs two rim cutters (the little cat ears). The bit’s faces need to be surface ground (otherwise the bit will fail to bore gouda). And the lead point should *not* be a screw. These lead-screw spades are a sin against the Chair Gods.
Spades can handle almost any angle – up to 34° off vertical with ease. They can be resharpened. You can adjust their diameter on a grinder in seconds. They are cheap and plentiful. And they don’t have the side-cutting problems that the two above bits do.
But they blow out the backside like an American tourist after 10 currywursts. So you need to clamp backing blocks below the arm and seat when you make through-mortises.
— Christopher Schwarz
*There are Forstners out there that have a long lead point – usually a replaceable brad-point bit. But they are hard to find. And expensive when you do.