I bought a set of HSS drills ranging from 1.0 to 6.0 mm diameter in 0.1 mm increments, (DIN 338,) in which I found that every drill is approximately
0.08 mm undersize i.e. nearly a size smaller than marked. Is this because of poor quality control by the manufacturer, or is it an attempt to allow for the fact that the resulting hole is always a bit bigger than the drill?Cliff Coggin Kent UK
Cliff,
Sorry if this is a 'sucking eggs' thing but were you measuring the shank or the sharp end? The shank usually is undersize somewhat.
Andrew Mawson Bromley, Kent, UK
A *standard* drill will usualy measure a little down.... up to 0.01mm this isdue to the tolerances they are made to, usualy always a minus tollerance rather than plus one (which would be a bit useless)
as the OP said, if you are measuing the shank of the drill rather than the flute, it is quite likely to be up to 0.1mm down on size, this is to give a small amount of clearance when drilling deep holes, although... theoreticaly you should never drill deeper than the flute of a drill.... but in practice.... we all do it.... i have extended drills by TIG welding extensions onto them in the past, with very few problems
HTH
Tim
Thanks, one and all. I was indeed measuring across the shank. On checking a few across the flutes (not so easy to find the maximum diameter which is why I measured the shanks originally,) they seem to be pretty accurate.
Cliff.
The ultimate test is surely to drill a hole in some scrap then pull out those inside calipers and a micrometer (or an inside vernier, of course) and test the result ;-)
ABS
The problem is that I keep losing my 1 mm internal calipers.
Cliff.
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