Was just down at Mark Housel's place (L&M Precision), and thought about this thread. Mark had spaced out on a work table a long line of slides and red dots, going through his process. But what made me really appreciate the machine work knowledge that was necessary for this business was the variety of adapter plates he was machining. There were not only those necessary for certain initial installations (e.g., a plate with an integral rear sight), but also those where a customer asked for a slide to be adapted so a Brand X red dot could be replaced with a Brand Y red dot. And more . . .
I'm sure there are quite a few talented people available to do this work. Still, it's nice to see first hand the variety of quality work that can be done. And Mark is a really nice guy too!