View Single Post
  #7   Report Post  
Posted to rec.crafts.metalworking
whit3rd whit3rd is offline
external usenet poster
 
Posts: 2,017
Default Drill bit tolerances

On Oct 2, 6:17*pm, "Michael Koblic" wrote:
What is the expected tolerance of drill bits? I have a set of fractional,
letter and number drills. No.12 to 15 (including 3/16") seem to produce the
same size hole.


I've used the shank of drill bits as gages; they measure within .001"
of
the marked size.

As for the holes, the #12 makes a hole bigger than #13 and smaller
than
#11 (i.e. look at the gap between sizes), unless it's dirty/bent/dull.
Fractional drills, some of 'em, have been off by .005" recently, but
they
might have been made-for-WallyWorld.

People who need real precision don't use twist drills, of course, for
the final dimensions.