On Wed, 22 Jun 2005 16:41:24 +0100, John Rumm
wrote:

The through hole had a
square cut slot (approx 5mm deep and wide) machined into its
circumference for a woodruff key.

Usually cut with a slotting machine, rather than a broach. This is like
a shaper, but skinny and with a long reach - they were the original form
of shaper and one of the first specialised machines tools. (A shaper is
a single point tool like a lathe tool, oscillating back and forth whilst
the work moves sideways beneath it.)

Internal splines are usually broached, but broach tooling is expensive,
and needs an expensive press to operate it. So if you're just doing a
single keyway slot, a slotting machine is simpler.