In a related subject:

When the depth of a drilled hole is called out it usually doesn't mean the
depth of the drill's point at the hole's bottom. Depth is measured from the
place on drill's end where the cone point begins. For example: A hole made
with a118 deg. drill (59 deg. angle from side to point) would need to be
drilled a little deeper in order to make the hole's full diameter reach down
to the specified depth. In other words, it is necessary to drill deeper by
an amount equal to the pointed portion of the drill. The math would be:
Extra depth = sin 59 x (1/2 diameter)

And it goes without saying (although someone will surely do it): For
critical depths requiring full diameters at bottom (drilled, then reamed
"square") the extra amount would be subtracted from the specified depth of
hole.

Bob Swinney


"Steve Lusardi" wrote in message
...
Ah HaH, now I understand! That's why those Rolls Royces cost so much!
Steve
"Robin S." wrote in message
.. .

"Randy Replogle" wrote in message
...

a "scale".

...and this is a "miscalibrated rule" to allow for shrinkage in molded
parts.

In my apprenticeship theory class, the "scale" is the little black
etched,
stamped or painted lines with the numbers which are on the "rule".

Interesting note, my instructor used to work for Rolls Royce and they
used
to have their 6" rules calibrated once a year (or more, I forget the
exact
cycle)...

Regards,

Robin