Re: Making Flat secondaries - disaster #1...

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Mike Kiser by way of Terry Fritz <twftesla-at-qwest-dot-net>" <clic-at-kiva-dot-net>

At last, a subject on this list that I feel competent enough about to offer
advice!
I've drilled many holes in acrylic (Plexiglas, Lucite, etc.) and
polycarbonate (Lexan, Tuffak, etc.)
and have had good results using a standard drill bit that has been modified
in the following way:
Carefully blunt the cutting edges right where the flutes (spiral grooves)
meet the bottom of the
drill with a grinder or whetstone. The small (1/32 to 1/16") flat that you
make should be at an angle
that would be vertical if chucked in a drill press. The edge should still
be sharp, but with a less
acute angle. The idea is to reduce the tendency to "screw" into the plastic.

I've never tried grinding the point to a wide angle but the idea of using a
starter hole certainly
sounds counter productive. In many materials the drill point is the only
thing that keeps it from
grabbing. This is why drills are much more likely to grab just as the point
starts exiting the back
of the work piece.

I hope this is of some use to this great group. I sure couldn't have built
my coil without access to
the information found here.

Mike Kiser

Tesla list wrote:

>   A real good bet when drilling acrylic and lexan is to grind your bit
> into a very wide included angle, the included angle should be around 160
> deg. so that it chips away at the material, not cutting into it.
> Also, I have found that straight mineral oil used as a lube on jig saw
> blades, or drill press bits and hand tools will allow a good clean cut
> with little cleanup.
>  drilling acrylic is much like drilling cast iron, (except for the
> melting at high cutting speeds) If slightly less then flat cutting
> angles are used it will peel the material out of the hole very nicely
> with mineral oil as a lube.
> Hope this helps,
> Marc M.
>
> >
> > Cheers,
> > Ralph Zekelman