It isn't the design process that I am thinking about. Say you have a
blueprint that calls for a 1 inch deep hole .138 diameter +/- .003 (
just so you don't worry too much about the diameter ) but true to the
axis within .004. Can you reasonably expect to drill it with a twist
drill? Since that requires that the angle be within about .25 degree,
my guess it might be possible with a rigid machine. But has anyone
here know if one could do it with one operation or is it something
that requires two operations and a lot more cost?

I agree that measuring is part of the problem.

Dan


"Robin S." wrote in message news:aAqJb.18138
Your design process in backwards. How accurate does it HAVE TO be?

If the exit location is .0023" from where the nominal location is, what
happens? What about if it's .0079"? Will the part not function correctly?

Do you have the capability to measure the location, size, profile and
possibly the roundness of the hole? Would you know if it was straight or
not? What if it has a bellmouth profile or bends as opposed to going
straight (but not necessarily concentric with the axis of the spindle)?

Perhaps these are obnoxious questions, but the tolerance gods don't work in
.0002, .001 and .005 increments...

BTW, you may want to go for parabolic drills. They are made for deep hole
drilling (generally beyond diameter:depth ratio of 1:4 or great, IIRC).
They're more expensive, however, than standard twist drills.

Regards,

Robin