Claudio,


Yes, my mic with the extra Vernier scale can "resolve" down to 0.0001.  However,
that doesn't mean I'd trust it down to 0.0001!


Starrett's current-production 0.0001 micrometer is specified as: Accuracy (in):
+/- 0.00005.  That's for the modern T221XL version with carbide anvil faces.


Mine has only the hardened-steel faces and an unknown amount of wear.  That's
why I think the last digit on my example would be "just a suggestion" !


John Ruth


________________________________
From: Claudio DeLorenzi 
Sent: Monday, November 13, 2017 3:23:29 PM
To: John Ruth
Cc: Ed Minch; Kirk Eppler; Tools Old
Subject: Re: [OldTools] Hot mic

Re Micrometers (I love precision tools!)
One of my small ones came with a small ball anvil, I guess for precision
indicating on round stock?  I can’t recall off hand if any of the small mics
came with any standard, but these were always estate sales or flea market buys,
and people often take out stuff from the cases if they don’t know the purpose of
the part.  You sometimes see the little wrenches and standards (even gauge
blocks) on sales tables, long separated from their micrometer or tool sets and
sellers who have no idea what they are.
   Don’t some of the vernier scale mikes measure in tenths so the resolution is
indeed 0.0001 (0.001”/10)?  One complete turn on a 40TPI thread is 1/40=25 thou
.   The main division on the mic thimble is in thou, and the vernier divides
each thou by 10, ie does the last tenth on the sleeve (or whatever that part is
called, with the longitudinal lines- and yes I realize that we are interpolating
a bit on these, and all we are really doing is narrowing the error bars).

   Even without the vernier, you can guess whether you are half way between the
marks (ie plus or minus 5/10ths, ie 0.0005).
  Either that, or I have been doing it wrong, haha.  Maybe a real machinist can
chime in here?  I don’t use these every day, so I don’t have a high confidence
level in my info.
Cheers from Waterloo
Claudio