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.
14 thoughts on “Different Bits for Different Angles”
I’m curious, what is the issue with a lead screw on a spade bit? I was thinking about picking up a set of diablo spade bits because I have had good luck with their other products in the past but now I’m glad I read this before spending my money.
They are fine for carpentry – the lead screw helps pull the bit through the wood. Reducing your effort.
But they are mostly crap for furniture making. The bit is in charge of how fast you enter the work. With a spade bit, the bit has to be spinning at a high speed to get a clean entry hole. A lead screw pulls you in before you can get up to speed.
Most people don’t believe this to be true. Buy one and give it a go.
Has anyone experimented with grinding the threads off of the lead screw on an auger bit (specifically Wood owl’s) to make a long pointed brad?
I’m sure this is a dumb question, but why is everything 5/8” in the world of chair making and not 1/2” or 3/4”? Those bits are easier to find.
It’s not a dumb question at all. With half inch tenons, they would be pretty weak, especially in the mortises into the seat. You could use three-quarter inch tenons, but the sticks would be really heavy looking.
Many Irish chairs use bigger tenons. So that is a good place to start if you are having trouble finding bits.
I just finished a child forest chair, Peter Galbert’s Drawing Chair design, which used 1/2 and 7/16 mortises.
LMAO at the currywurst comment. Went to a place in Frankfurt called the Best Wurst in Town and the spicy one was not too friendly on my digestive system.
I saw a demonstration once by one of Thomas Moser’s craftsmen who was building one of their continuous-arm Windsor chairs. He was boring the holes for the back spindles in the arm/crest with a spade bit which was ground to have an extra long lead point. It didn’t look like it was ground very neatly, but it worked very well even for the spindle holes at the side of the crest which are at an extreme angle. Of course he was doing this all by eye and fairly quickly, so experience played a big part.
Thanks for the clarifications Chris, this really helps.
Hi Chris. Thanks for the article on boring bits.
You mention that you can “adjust the diameter of your tenon cutter”. How do you do that? If it’s not one of those fancy Veritas ones.
And you also said you can “adjust the diameter of a spade bit on a grinder”. How do you do that? Wouldn’t you have to precisely take equal amounts off the edges of that spade bit by eye relative to its centerline?
Some tenon cutters such as the Veritas and others are adjustable. Plug cutters are not. Sorry that wasn’t clear.
Grinding spades is easy. Grind both long edges of the bit for the same (very brief) length of time. Then drill a test hole and measure that. You don’t have to remove exactly the same amount of metal from both sides. Just get it close
As a comparison, how well do the old fashioned bits for braces work for boring at an angle?
Two different (and rare) bits do drill at angles quite well. The first is an auger with a screw, but the cutting edges curve down. Known as a Cook (Ransom) type. The second is an original Forstner bit with a solid cutting edge. The originals are very rare. They cut beautifully at very steep angles. A later patent put slots into the cutting edge to reduce the heat buildup when using power tools (belt driven). The current versions have opened up the slots so wide that boring at an angle by hand is almost impossible.
Comments are closed.