Everybody walking past said "You need a wood lathe for that".
However I learned how to turn the lathe handles in the complicated
fashion needed to make the curves of the knob. I finished off with
some bits of sandpaper. I didn't use an angle grinder!

Here's the finished knob and the scrap timber that I made it out of:
http://i40.tinypic.com/34rvibs.jpg

I think it's mahogany. Inside the knob is a metal bearing. The knob
turns on the metal spindle. I had to use a boring bar to widen the
hole to half way down. I'm not sure how I could do that on a wood
lathe. Anyway I like to keep my hands well away from spinning objects.
The round bit of timber is a plug for the top of the hole.

Here's a very old knob of a different design:
http://i42.tinypic.com/r1djl4.jpg