In article , W7TI
writes:

On Sat, 8 Nov 2003 13:27:07 -0000, "uk-hamman"
wrote:

HAVE YOU EVER HEARD OF
DRILLING LOTS OF SMALLER HOLES AROUND
THE DIAMATER , UNTILL THE CENTER DROPS OUT
AND THEN FILLING THE EDGES SMOOTH

THE GOOD OLD FLE WORKS WONDERS ...HMMMM
_________________________________________________ ________

This is how our Neanderthal ancestors did it, and if it was good enough
for them....
--
Bill, W7TI

Practically speaking (as one neanderthal to another...):

That method does work if there's no drill press available. But, be
sure to buy an extra drill bit for the size desired going around the
rim. Had to do that with a 4 1/4" diameter speaker hole in an 1/8"
aluminum rack panel (alloy tougher than 2024 but not as stiff as
6061). That included light oil lubrication. The "center" didn't
"drop right out" but centerpunching the many holes right allowed
using old wire cutters to snip the narrow left-overs between holes.

A Hand File to complete?!?!? Good grief, no. A Dremel Moto-Tool
with several "mill type" cutter bits is much preferred to smooth out
the rough edges. Note: Home Depot, Lowe's, Do-It-Centers, OSH,
all carry extra bits for Dremel Moto-Tools, many which aren't
included in the Dremel kits. Use a biggie mill cutter to hog out the
worst, go to a small bit to smooth those edges. One of several
grind wheels can be used to finish it off. Takes a steady hand
(usually both hands if panel is in a vise).

Absolutely needed: A scribe marked circle on the panel as a guide!
Maybe two concentric circles, the inner one slightly smaller than
desired as a "target." If one gets sloppy, it's possible to cut farther
out than the inner, smaller "target" circle. To get the scribed circle,
use a grade-school compass in REVERSE, the "pencil" part in a
small drill hole at center, the "center" part (pointy end) doing the
scribing.

Dremel also makes a dandy mini-drill-press stand for the Moto-Tool
which is just lovely for through-hole PCB drilling. I use one for that
plus the AC line voltage adjusted with a Powerstat (Superior Electric)
variable autotransformer to control the "drill press" speed. BTW,
liquid hand soap, slightly diluted, works out as a PCB drilling
lubricant and washes out with hot water...and can be used with a
rough-surface sponge to buff out surface oxidation on the copper
foil or removing tiny burrs in the drill holes.

Len Anderson
retired (from regular hours) electronic engineer person