"Dan Caster" wrote in message
m...
I looked in all my reference books and could only find data in the
Machinery Handbook on the size of drilled holes. Nothing on how
straight drilled hole can be expectd to be on a routine basis. And
obviously nothing on how straight a drilled hole can be expected to be
when done by a skilled machinest. Does anyone have some data on this?

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

I'm not convinced that there are any standards, Dan. When this topic was
aired some time ago, Bill D sent me some pictures in which he had
outstanding success in drilling deep holes in stainless. In essence,
there's always the possibility that the drill will go straight, but also the
possibility that it won't, which is why I always say that twist drills do
not drill straight holes, which, in general, they don't. Than again, what
does "straight" mean?

I'm of the opinion that one can expect anything from dead on to enough
runout for the drill to bind in the hole. I've seen it both ways in my
years in the shop. Lots of things cause variations, right down to personal
application. It's a good policy to always assume it won't go straight, so
if it's important that it does, you take precautions that will prevent
making scrap. By suggesting that twist drills don't drill straight holes,
it more or less keeps the idea fresh in your mind.

Harold