Gregory's Server@tubetime @f4grx The plunge hole shows that they did this as fourth axis mill work instead of lathe work, as far as I can tell. This should be lathe work, I think, for a better sealing surface. Lack of knowledge of design for manufacture and process selection seems to jive with the overall collection of 🤦 here, as far as I (just a hobby machinist) can tell. If I'm wrong, I'd love to learn!
Adam the Machinist had a potentially relevant video recently that was talking about undercuts including plunge holes, but not about mill vs. lathe work: