A Watts drill is not the same as a rotary broach. I can't explain the difference, but there is one. Quoted from the
Woodworkforum;
http://www.woodworkforums.com/archive/index.php/t-142453.html
By Pete F
"I think rotary broaching is actually a different principle to that shown above. IIRC, with a rotary broach, the broach is held stationary on the work and "wobbled" by an eccentric, hmm, not sure how to describe it, I'll say "cam" but I'm sure somebody will shoot me down for that as it's not really a cam at all. Anyway, an eccentric "plate" behind the broach that wobbles the broach from side to side and drives it through the pre-drilled hole. I intend to make one of these, but just haven't had time ... hence why I'm typing while sitting in Tokyo!
On the other hand the one above is a "Harry Watt" drill bit. As I understand it, that rotates pretty much like a normal drill bit, BUT the drive to the specially shaped drill bit ALSO rotates. It's really tricky to describe, but I think it showed it on the video in the link. Imagine getting your drill press quill, mounting that offset on a plate, and also turning that around in a circular shape. Ok that's a really **** description, sorry you'll just have to look at the videos. Google "Harry Watt", he was a clever dude. Edit: Oh, just watched that video, ok, yes that would be another way to rotate the drive, run it through a fixture with universal joints so the axis of the drive is changed. Very cunning. Anyway the point is rotary/wobble broaching, and Harry Watt drill bits work on quite different principles, so may be confusing when intermixed in posts. Both pretty clever, but as mentioned, I've heard the former is better for a number of reasons."