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I think I would put the reaming size drill in for the 3/32" hole in first then plunge with a slightly undersize 3-flute milling cutter down to the end of the valve guide to get most of the waste removed before following up with a form tool to do the recess around the guide.Rather that thinking of a turning tool as the form tool you may be better with one turned from silver steel and one or two teeth cut on the end, giving the swarf somewhere to go will be the main issue.After that ream and turn the valve seat, I never use a seating tool if I can get the part into the lathe to turn the seat and don't have to spend much more than 60second lapping in the valves and not motoring the engine to bed things in and always seem to get plenty of compression.
It might be fiddly in these sizes, but have you considered milling the annular feature using a rotary table rather than boring it? It gives you more control over cutting tool pressure, speeds etc €0.0000007 supplied,AS
I figured I should follow up and close out my original question so future me and maybe others will know what I did.The end result was I made these valve guides, rather successfully, on my little Emco Compact 5 CNC lathe, after much trial and tribulation.The process was as follows:The end of the program sets the profile tool to the right spot to be a stop for pulling more stock out for the next part.I faced the end off, then center drill, then drilled through with the appropriate drill (peck drilling)The next step and the tricky one was to use a custom ground D-bit type tool to make the pocket - but the tool isn't a "form" tool, its just made to fit the deepest reach of the pocket, and then the program controls the profile it cuts. It was a squeaky / chattery process but successful none the less. I effectively made a deep face groove near the bottom ID, then went back and opened up the outer OD, then one last time to profile the inner cone. Profiled to size outside and then parted off.The spring pocket was then done in a separate operation on the other end.So in summary the solution was a custom boring bit / D-bit.There was more to it than that - but the other stuff was down to the lathe not being OK on many fronts. Hopefully all thats behind me now.