Originally Posted by
TomD77
I do gunsmithing on occasion and have some high accuracy measuring tools. Not to that level but I know that they exist. I know that turbine blades in the "hot" section of a jet motor have to be machined to incredible accuracy.
I've got a Mitutoyo digital caliper that goes 2 decimal places and a older manual Starrett micrometer that measures directly to .004 and interpolated to closer. They are fairly expensive devices but not in the ballpark as what a top end machinist would have.
I have an antique 1" Lufkin mike with a secondary vernier that indicates in 0.0001 (ten-thousandths) inch, but it hasn't been maintained, i.e. zeroed, lubricated, play-adjusted, and checked for tracking accuracy. A thousandth of a millimeter corresponds to about 0.4/10,000 inch, about half of a ten-thousandth of an inch. So when calibrated my mike would probably not indicate a difference of .001 mm between two measurements, but it's close - its resolution ONLY needs to be doubled to be able to measure that. One way to do that is to simply remake the mike with larger barrels so that a tighter vernier scale could be read, or add a magnifying attachment of some sort. This assumes the screw is calibrated will enough to perform to this level.