I think it was parallel sided spline it was a old tractor cel on the transmission I beliveDepends whether it is an involute spline or a parallel sided spline, if involute spline it needs to be identified and a cutter bought or rented, if parallel sided, it can be milled to with ganged slitting saws, then a center cut to remove the intervening material between the parallel sides.
Tim it depends on the material. if you are cutting external splines you can grind a round piece of HSS to a proper shape cutter and use that new dividing head to cut it. Even parallel splines will have a slight tapper but if you are careful they can be cut with a slitting saw, it may require slight adjustments in angle though.I think it was parallel sided spline it was a old tractor cel on the transmission I belive
It looks cool to make shafts, maybe I had too much coffe.If it was parallel sided I imagine you could use a single end mill provided it was a standard size