Steve, thanks for you comments.
Next came the locking cam, which aims to lock the tool holder in position, in an angular handle movement of 45 degrees. The basic turning was done in the four jaw chuck, then set over to machine the cam. Finally, the height had to be machined, to provide a close running fit in the tool post. The chuck was first changed to a 3jaw. A hard wood mandrel was turned with a slight taper to fit the bore of the cam, and a fixed steady used at the other end. Light cuts were taken to carefully machine the bottom to size.
Cheers David