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?

Drilling Square Holes [Scott Smith] [via]
A Simpler Explaination [MathWorld]

Note: A commenter on Digg notes that these are also called “rotary broaches” and found some from Slater Tools (pictured above). [link]

Related:

### 6 Responses to Tool Tech: Square Drill Bits?

1. Nick Carter says:

I have a set of the Watts drills and have been meaning to work up a page showing them…when I get around to it I’ll drop a line. The drills are very cool.

I have been thinking seriously of expanding my Make article to a full pamphlet on all the methods of making square and polygonal holes. Someday…

The rotary broaches are different than the watts drills in function. Watts drills are true drills where the rotary broaches are, well, more broachlike.

2. Trey says:

These are cool!! Where can I buy some of these drills? I don’t
even know why I need them but I do.

3. Yes, rotary broaching is different than the rotating drill bits. The rotary broach tool holder positions the broach at a one degree angle to the part. The broach rotates with the part, but because it is at an angle, it cuts the part one corner at a time. Rotary broaches will cut squares, hexes and more. The best way to visualize it is to watch the video at slatertools.com.

4. See more users of Rotary Broaching tools at the Rotary Broaching Showcase: http://www.rotarybroaching.com.

5. Yes, the image above comes from the Slater Tools website. http://www.slatertools.com

6. You can also order these tools online from Polygon Solutions at http://www.buybroaches.com They have an amazing rotary broach tool holder with a superior bearing pack and pressure relief vent hole.