Bill Darby wrote in message ...
Sy wrote:
So my question is when drilling a 1" deep .138 hole, how much should
one expect the far end of the hole to be from the ideal?
Dan
Hello Dan,
There is a military standard for drill hole size tolerances. It is
AND10387. See http://www.bjg-design.com/designbook/holest.htm
Also look at http://www.bjg-design.com/designbook/drilld.htm for drift
tolerance for drill holes. Also look up
http://www.bjg-design.com/designbook/formhsiz.htm for positional
tolerances.
Sy
Hi Sy
I to appreciate having these tables as a guide. What I do wonder about though, is if there are any
qualifiers on these values. IE are they applicable to a drill press, a mill or a lathe and in any
particular material? (or just drilled holes of any kind any place with any kit)
Hello Bill,
Before retirement,I was a machine parts & tooling inspector at the
aircraft companies. I did not drill holes, just checked them.
Sorry,I can't answer your question(s). Good luck,
Sy
The reason I ask is that on a lathe I routinely drill 3 to 5" deep holes in Al with accuracy that this
data would achieve at only an inch or two. IE this is a letter I wrote detailing what happened when I
tried drilling a deep hole with an intentionally off center ground drill tip.
The letter***************
I just wanted to say that even the tip geometry is not to important in maintaining a
straight hole. (At least not in Al as per this illustration.) I did the hole in the
picture with one flute purposely sharpened to be twice the length of the other. That's a
5.125" long 1/2" Al rod and the exit hole was .005" off of center and the entrance hole
was about .002 off of center. (going by memory)
It's not a pretty hole as the tip of the drill found the center of rotation and the long
flute swung wide for the entire 5 inches and acted like a boring bar, using the point at
the center of rotation to pivot about. The drill was about .145" and the hole it drilled
was about .190. That math is just about right when you consider that the long flute was
about 2/3 of .145 is .097" so it should cut a .194" hole if it acted as a boring bar. It
did!,,,, so it must have been acting like a boring bar centered by the tip on the center of the axis.
Actually the exit hole was about .145" but I could see that the entire length of the hole
was much larger, so I turned a few thou off of the end to expose the actual size of the
hole.
As far as I can see, was that once the tip reached the end and had no more metal to stay
centered in, it reverted to acting like a drill and just cut a normal sized hole through
what material was left.
My thoughts anyway.
Bill D
*******************
I do understand what standards are but at the same time I would expect that anyone could achieve similar
numbers in similar conditions and I know that the chuck I was using was a couple of thou out of whack to
start with.
Bill D
(I know that I should not post this) (0: