On Wed, 8 Jul 2015 16:39:16 -0700 (PDT), "
wrote:

On Wednesday, July 8, 2015 at 6:36:37 PM UTC-4, Lloyd E. Sponenburgh wrote:


When did 0.468" become a "largish" hole? What we want to know is the make
and model of the drill bit. That's an extraordinarily good life for a
'common' twist drill... split point or not.

Lloyd

.458 is not a largish hole. But the annular cutter I bought is a 20 mm drill. Not all that large, but big enough that I would drill a pilot hole if using a regular drill.

Dan
My son was working at a boat builder and they were having a terrible
time drilling a 1 inch hole through a 3/4 inch thick 304SS plate. He
suggested that they let me try. So I got out a small drill, 5/16 I
think, and drilled through pretty fast. Then I put the 1 inch drill in
the machine and slowed it way down. My son was surprised about the low
RPM of the drill. I told him it was the correct RPM. I then proceeded
to drill through the plate with a heavy feed. So the whole thing took
about 5 minutes. Drilling a hole to provide clearance for the web of a
larger drill can really speed things up. On the other hand it is not
always necessary. I have a repeat job where I drill a 7/8 hole 2
inches deep in 6061 aluminum in 1.6 seconds. The part is spinning 3000
RPM and the drill is fed at .016 IPR. Well, really, the CNC lathe is
doing the drilling. The spade drill I use has high pressure coolant
through. If someone turns off the coolant for some reason and presses
the start button the spade drill and part are destroyed. I know this
because an employee twice forgot to turn the coolant back on after
turning it off for some reason. GRRR.
Eric