On 8/21/2013 14:25, Mike B wrote:
This is for a searchlight application where the light source shines backwards
into the reflector which then reflects the light forwards producing a narrow
beam.
The reflector needs to be about 2 to 3 inches in diameter with a focal point
about 2 to 3 inches in front.

Presumably this was possible in the days before CNC machinery, so how did they
do it?

I remember someone casting one from resin.. Make a container that
SPINS (rotates) and put the resin in the spinning container.
RPMs decide the curvature of the resin. I remember they used a
LP player to get an even RPM. After it has hardened, coat it
with silver or other reflective coating.