Turning these fairly simple pieces should have been a doddle. Trouble was that they are relatively thin and soft and holding them in a three jaw chuck on the lathe was OK, until the rather sharp tool got pulled into the work. The cutter jammed, the workpiece was pulled out of the chuck and thrown across my workshop, with a a lot of superficial damage to the workpiece.
Fortunately, there was enough material remaining to machine out the dents and cuts. Also, it forced me to make a jig to hold the workpiece securely. Since the head caps are all different sizes, I had to change the jig dimensions after each head was machined, which was time consuming, but the method worked well with no further hitches. Also, I changed from a tangential, sharp, high speed steel cutter, to a neutral rake carbide (and therefore less sharp) one, and no further dig ins were experienced.
Next I will drill and taps the holes for the small bolts which secure the head caps. All 56 of them. I sense some more CNCing in my near future.