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[Ian B]

With that depth and aspect ratio, you're going to have troubles! Not only with machining out the annular ring, but then also with the threading (I'm guessing you mean an external thread on the 3/4" diameter section, yes?).

If the part could be made in 2 pieces and assembled after threading, you'd make the whole job *hugely* simpler.

Ian

[Carm]

1.7" deep is a LONG way if the groove isn't wide enough to allow for a very stiff bar style tool. I foresee a case of near terminal chatter in your future.

Steel simply is not that costly to justify trying to save the core.

Think hoop, not beam.
If design permits, two piece sounds better.