If we look at the surface being drilled - the center of the drill
the cross point helps on the drill or spade - the surface speed is all
but zero and the drill is pushing itself through. Further out there is
cutting because surface speed is reasonable.

Martin

On 7/9/2015 11:16 AM, wrote:
On Wed, 8 Jul 2015 18:40:46 -0700 (PDT), "
wrote:

On Wednesday, July 8, 2015 at 8:34:26 PM UTC-4, Lloyd E. Sponenburgh wrote:
" fired this volley in
:

Not all that large, but big enough that I would drill a pilot hole if
using a regular drill.

I might 'pip' the hole to make sure it started without any vibrations, but
pilot? (I assume you mean full-depth) With THAT small of a bit?

If my machines can't hold center better than that, I'd better quit or
rebuild their spindles! G

Lloyd

The pilot hole is not to make sure that the machines hold the center .

It is to eliminate the pressure needed to have a decent feed rate.

On stainess as Eric describes it in his message, it makes a huge

difference with normal hobby grade drill presses. If you do not do that ,

you end up work hardening the stainless and or stalling the drill press.

Sure if I buy an industrial grade drill press, it is not necessary. B

ut this lets me use a cheap ( less than $600 ) drill press.

I just can not justify spending more for a drill press since I do not do
production work.

Dan

Dan
Greetings Dan,
If I was drilling the same hole in one of the CNC machines with a
twist drill I would still drill a pilot hole just because it would put
the hole in faster. With a coolant through spade drill and the 15 HP
CNC lathe I would probably drill a 1 inch hole in one shot. But I did
a job where I had to put a large hole in several 17-4 PH SS parts and
even though I used a coolant through spade drill the hole was so large
that I drilled a pilot hole. I was able to then nearly triple the
spade drill feed compared to using the spade drill to remove all the
material.
Eric