Spiral phase plate looking for advise on making shape..tia sal

I think that in the absence of access to an NC machine, rather than attempting to machine it directly I'd look into making a mold. You should be able to get something approximating the form from a piece of thin plywood or plexiglass--cut a disk, cut that radially once, put in a spacer to maintain the step height, and bond that into the end of a piece of pipe, then pour acrylic casting resin or whatever you need in to an appropriate depth. Make sure you wax everything up thoroughly.