DoN. Nichols wrote:
Mount it in the lathe -- either in a 3-jaw chuck, or a 4-jaw
chuck and take the time to center it well. (And you may wish to use the
lathe to bore it to a nice concentric and smooth ID.)

Then -- take the boring bar for the lathe (one of the old ones
which accepts HSS lathe bits ground to shape for boring), and grind a
new bit for it -- with the tip as wide as the grooves in your splines,
and with whatever shape you want. Mount it so the profile is end-on to
your workpiece.
...

My first thought was to machine a male spline on a piece of drill rod,
turn the end down in steps. Harden and temper and use as a broach. I
think that would be easier.

Ted