Our friend Joe Brown over at PopSci sent us this bit of tool tech (from Digg) today — it’s the math behind square drill bits. No, we’re not joking; there really are rotating drill bits that’ll drill square holes.
These bits are based on known as a Reuleaux Triangle — a triangle that looks like it’s been inflated to 10 psi and is shaped sort of like a guitar pick. There’s lots of math involved, but essentially this shape can rotate within a square of the same width, though its center must follow a circular path in order to do so.
Early last century, Harry Watts created a patented system for drilling shaped holes by adding a gearbox in the drill’s chuck to allow his special bits to simultaneously rotate and revolve. By changing the number of flutes on the drill and the shape of the gearbox, he created bits for drilling numerous shaped polygons.
Do any of you have experience with these?
Note: A commenter on Digg notes that these are also called “rotary broaches” and found some from Slater Tools (pictured above). [link]
- Toolmonger’s TV Tonight contributor Nick Carter wrote a great story for Make describing 14 ways to make square holes in aluminum sheet metal.
- We made square holes as part of our How-To: Add Rear Exit Handles to Your Truck post a while back.
- One of Nick’s methods involves filing, and this (among other reasons) is why you should have a good set of files.