Re:Diamond hauled from deep inside Earth holds never-before-...
by JshWright on Sunday January 23, 2022 @12:35AM
(#30043891)
Yeah, that's why tenths (~2.5 microns) are used when thousandths aren't precise enough.
I'm definitely not claiming it's a good, I'm just describing the system I have seen used in the handful of machine shops I've spent time in.
Re:Diamond hauled from deep inside Earth holds never-before-...
by jbay808 on Sunday January 23, 2022 @12:48AM
(#30043933)
I think YZF just mis-parsed your sentence, and thought you meant a thou is for very high precision work, while you meant that a tenth is for very high precision work.
(That said, I'd add -- measuring to one part in 10^6, for anything except time, is challenging but still very doable; machining to one part in 10^6, for anything beyond very simple shapes, does require pretty exotic methods or very great care, and to verify it you have to measure to one part in 10^7).
EDIT: There's this rule of thumb (I might be getting this slightly wrong) that one in a million accuracy/precision is about what you can expect to achieve without resulting to exotic means (at least order of magnitude). So microns of flatness over a meter e.g. Trying that with imperial units just breaks my mind, what's a million mils. Sure I can calculate that. But it's like a pretty useless measure. So accuracy of one thou over a million mils is sort of weird. (1000 inches which I'd have to translate to some normal unit... 25.4 meters ;) ).