On 12/10/16 18:24, Bob La Londe wrote:
----- Original Message -----
From: "David Billington"
Newsgroups: rec.crafts.metalworking
Sent: Tuesday, October 11, 2016 2:38 PM
Subject: Square holes...

That's called a rotary broach, and last time I looked they were pretty
pricey.



I think actually a different beast as a rotary broach has the same form as
the shape it cuts whereas a square hole drill has 3 cutting edges as shown
here http://www.integerspin.co.uk/polygon.htm and operates in a different
manner to a typical rotary broach.
Ok, maybe, but Polygon calls them rotary broaches.
https://www.youtube.com/watch?v=smTdkevMMTc


That is what I would call a rotary broach as it uses a 6 sided cutter to
cut hexagons etc, what Jon mentioned that you responded to was a polygon
drill where a special drill with 1 edge less than the number of corners
in the hole you want is used. See
https://www.youtube.com/watch?v=rjckF0-VeGI , a different beast to a
rotary broach.