Homebrew PCBs

designer_craig wrote: 
> 
> I am looking for the surface feet per minute and feed per turn numbers
> for small carbide drills in FR-4. My 5400 RPM maximum going to be
> well below the 30,000 to 60,000 RPM used by a real PCB drilling
> spindle but it should still work fine if I use the correct feed rate.
> Anyone got a reference for these parameters.

I would point pages 24.16 and 25.8 from printed circuits handbook 6th
edition. But nothing real there, you need cutting speed (sfm) and chip
load values from your laminate datasheet, but i never found any of those
values for any laminate i have used. I use 'guessed' values after
stressing with this plenty of times too. But never got results as good
as i wish.
http://books.google.pt/books?id=g9Q8RekeKaAC&pg=PA5
http://books.google.pt/books?id=g9Q8RekeKaAC&pg=SA25-PA8
The same book also points 500 as sfm and 1mil for chip load as normal
values for fr4. I use this as example from one laminate:

Suggested Drilling Parameters For Isola DE104i
                SPINDLE   Surface Speed
DRILL SIZE      SPEED      per Minute    INFEED      CHIPLOAD
inch     mm       RPM     SFPM    SMPM    inch    meter mil    mm
                                          min.    min.  rev.   rev.
0.010  0.2540    89,763    235      71.63  65     1.651 0.70   0.018
0.015  0.3810    80,214    315      96.01  80     2.032 1.00   0.025
0.020  0.5080    60,161    315      96.01  90     2.286 1.50   0.038
0.025  0.6350    53,476    350     106.68  80     2.032 1.50   0.038
0.030  0.7620    47,747    375     114.30  85     2.159 1.80   0.046
0.035  0.8890    43,654    400     121.92  88     2.235 2.00   0.051
0.040  1.0160    42,972    450     137.16  107    2.718 2.50   0.064
0.050  1.2700    34,377    450     137.16  85     2.159 2.50   0.064
0.060  1.5240    28,648    450     137.16  72     1.829 2.50   0.064
0.080  2.0320    21,486    450     137.16  55     1.397 2.50   0.064

Similar to what i did for me i put this on a spreadsheet and trunk the
rpm to 5400 and reduced the feed rate proportionally to the rpm
reduction. But i give no warranties.

drill   speed   feed
inch rpm in/min
0.01 5400 3.9
0.015 5400 5.4
0.02 5400 8.1
0.025 5400 8.1
0.03 5400 9.6
0.035 5400 10.9
0.04 5400 13.4
0.05 5400 13.4
0.06 5400 13.6
0.08 5400 13.8

You put so many effort, dedication and cost on the bridgeport that you
may like to build a smaller, lighter and faster machine just for pcbs. 

Simao