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I almost finished the setting micrometer yesterday before again running out of time. While the base does not have to be perfectly flat for it to be completely functional, slight rocking would be annoying. So, I accurately clamped it in the vise and faced it, as shown in the first photograph.
I then reset it in the vise and tapped two holes for attaching the micrometer assembly, as shown in the next photograph.
A third accurate repositioning allowed me to drill the hole for the pilot. To do this I carefully positioned the center of the drill 0.500" from the end of the fully-extended micrometer head and on its centerline. It turned out the ⅜" carbide drill bit I have is long enough that I didn't have to extend the depth using an ordinary HSS drill bit. The only remaining task is to hone the hole for the ~0.01"-larger diameter of the bottom of the pilot.
The last photograph shows a mock-up of the final tool.
The bottom of the pilot is tapered so it sits in the ⅜" hole.
The base could be ~1" shorter so I'll have to decide after I finish making it, whether I'm finished making it. There's no functional reason to shorten the block so I'll probably leave well enough alone.
Before someone raises the question, yes, I agree, this is quite a bit of trouble to go to for a tool that I'll rarely use, and that my daughters will throw out sometime in the future because they don't know what it is. But, arguably, it will be easier to use and more precise than the commercial version, and it didn't cost $450. However, the real reason for making it is that I have a love of precision instruments, wanted to make it, and could make it. So, I did.