LOL no I know nothing about machining
I close my eyes when I am milling or turning, seems to come out better that way
Fact is I am involved in CNC machining with all my housings and other parts, and to me the CS adapters often look like they were hand machined, but reality is they are running the machines too fast. The 3mm spinner hole is a perfect example of CNC being run too fast, 50% of them were off centre, now my guess is the machine is not off centre, just the speed at which it runs causes the bit to go off centre most of the time. If I slam the tailstock in too quickly on my own lathe I can get an off centre hole. Same with the cheap alloy housings, look at the cut marks and finish and dimensions and its obvious the machines are being run fast in order to make as much product per hour as possible. Go look at the finish on one of my housings and the differences are very apparent. We run the machines much slower especially for the finishing passes, part cost is directly related to time used to make it.