Some additional comments and opinions: 1. Precision drilling with a 3 flute stubby carbide drill is a good way to achieve +/- 0.001 size tolerance in certain m

Some additional comments and opinions: 1. Precision drilling with a 3 flute stubby carbide drill is a good way to achieve +/- 0.001 size tolerance in certain materials and size ranges, close to what you can get with a reamer and blisteringly fast speeds. 2. For long holes, guide drilling with a stubby drill is superior to spotting for orientation, and does just as much for position. 3. Spotting at 75% of the finished diameter isn't usually necessary, it's better on small sizes to pre-chamfer using the spot drill to 130% or spec rather than post-chamfering. Most holes would want to have a chamfer. 4. Optical comparators are useful for profile measurements. 5. Go/no go gages are not well characterized as a cheap and easy way, they are the final say and represent both the state of the art in metrology and the actual geometric definition of the tolerance limits for size and any other geometric control that you care to specify. For metrology of very tight tolerance holes and bores at small sizes, precision ground gage pins are the most expensive way to go and are irreplaceable. For larger bores, 2- and 3- point bore gauges and micrometers are to be seen as a necessary evil. I view 2 point spherical gages or micrometers as superior to 3-point cylindrical mics, because they tell you much more information about the bore shape. 6. The best designers avoid tight tolerance features except where strictly necessary. 7. I would tend to avoid straightness, cylindricity, and circularity, when tolerancing holes, and focus on the more general concepts of size, position, and surface profile. 8. Diameter compensation offsets are usually easier to adjust in the machine control than adjusting the boring tool, and can usually get close enough, especially on a horizontal CNC milling machine.