Jan,
The big professional drilling machines all use electric spindles but
some have air bearings for rotation. These air bearing spindles have
no ball bearings and therefore no metal to metal contact. Everything
spins on an air cushion with almost no run out. Very small holes can
be drilled with this type of spindle. The spindles are electric
driven to obtain the torque needed especially for larger holes.
All of my machines had ball bearing spindles, however, the spindles
did slide up and down in a cushion of air for very fast action. The
XY table also rides on an air cushion against the granite table.
My favorite machine was an Excellon EX-200 Driller/Router. This was
considered a "small"(6500 lbs!) machine. It had three spindles and
could drill or route three stacks of panels up to 12" x 24". It also
had an optical scope for digitizing. We used this machine for all of
our engineering and prototype work. The original specifications said
this machine could drill 400 holes per minute. This was probably true
for a .1" grid drilling only one deep. Our average drilling rate was
around 150 holes per minute when drilling three panels deep.
I shut off the auto tool changer mode since it just wasn't reliable
(ask any Excellon service tech!). Several types of spindles were
available but I used the 60,000 rpm drill/route spindles on the EX-
200 and 80,000 drill only spindles on the other machines. The air
requirements for these machines was about 20 cfm at 90 psi.
Tom
--- In Homebrew_PCBs@yahoogroups.com, JanRwl@A... wrote:
> In a message dated 1/15/2003 2:29:33 AM Central Standard Time,
> twb8899@y... writes:
>
>
> > Hope this info answers some of the bit questions.
>
>
> Wow! Thanks, Tom! That is VERY useful to us hobby-folk!
>
> Yeah, I watched a 4-quill CNC PCB-drill with "pods" change its own
bits, and
> all SEEMED to be fine, but I just could NOT help thinking, as I
walked away,
> "This CAN'T be so reliable ALL the time?!!!" GOOD to hear it isn't!
>
> Interesting you say the quill motors are electric. I was told they
are
> PNEUMATIC, to run at 100,000 RPM! Hmmm...
>
> Jan Rowland
>
>
>
>
>
> [Non-text portions of this message have been removed]