Homebrew PCBs

I am surprised at the air consumption and that they would use 
electric motors for drilling.  the motors would be much bigger than a 
similar power air motor.

Dave




--- In Homebrew_PCBs@yahoogroups.com, "twb8899 <twb8899@y...>" 
<twb8899@y...> wrote:
> 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]