I got the piston valve done today. I needs a close fit to the .515" reamed hole in the cylinder. The closest size I had was .750" so I started with that an turned it down until it just fit the opening in the cylinder. The valve was then drilled with a #11 drill for most of the way through and then finished with a #21 the last little bit for tapping 10-32. This also allowed tailstock center support for the rest of the turning (photo 1). The narrower part in the center section of the valve was roughed out with tool shown in photo 2 and then finished with a ground round nose tool to form the radius at each end (photo 3). Once it was parted off and the cut off end faced to final length, both ends were counterbored .025" deep by .375" diameter and the threaded end was tapped (photo 4). The finished piston is shown in the last photo, Tomorrow, I will make the shaft that completes the piston valve assembly.
Bill