Richard J Kinch wrote:

D Murphy writes:

Do I follow that action correctly: the cutting tool is tracing out an
internal hex path by spinning axially and wobbling at the same time?

Actually you are broaching with a hex shaped broach in the case we are
taliking about.

OK, then, does this 1 to 1.5 degrees of tilt and wobble result in a
slightly conical hole being broached, or is perhaps the tool tapered so
that the leading edge is wider than the body, or what?

The leading edge is wider than the body.

Since the tool is always at a 1 degree angle to the work, the sides of
the tool must have a 1 degree or greater draft.

Ideally the tool advances at the same rate that it cuts. So a 1/2"
diameter tool should advance at 0.009" per revolution. 1/2*sin(1). If
it advances any faster than that then the tool becomes choked, if it
advances any more slowly then you get an interrupted or zig-zag cut.
Since all work material is elastic, you would actually cut a little
less than the ideal rate just to release the load on the non-cutting
edge of the tool.

There is some spiraling of the tool as it cuts, so the bottom of the
hole may be rotated with respect to the top of the hole. Spiraling may
be undesirable because it binds the body of the tool and prevents it
from wobbling freely. One solution to this is to reverse the rotation
in mid cut causing the tool to spiral in the opposite direction.