Re: [CAD_CAM_EDM_DRO] Re: Creating long straight edges

Ah yes wires and lasers.... I have used them both.

I used to use the smallest diameter piano wire stretched with a weight
and corrected for catenary droop. I had a cheap microscope hooked to
a sliding carriage that allowed me to see a thousandth or two deviation
between the wire and a reference. I had to put little paper stickers on
the wire so it would not vibrate and be a blur.

With the lasers poor mode structure and fraunhofer difraction limit
the spot diameter. Amazingly if you put a very small pinhole in the
beam it will eventually cause the light to diverge more! The spot
will have a central fuzzy area surrounded by concentric rings of
intensity K (sin theta/theta)^2. But that will only get really bad as
the pinhole gets smaller than 10 microns or so. I think you could
get a pretty small spot by using a field stop...in other words
use two pinholes and the laser all in a line. With a cheap CCD
tv camera chip you might see a thousandth between pixels.
Give it a try!

These days I just use my $80 level that can see tenths.
I know that I am making spherical surfaces, not flat.
(the earth is round!) Lets see (grabbing calculator)...
curvature of earth is 0.3 millionths"/ft...ha ha no
worries I think...

Les

Leslie Watts
L M Watts Furniture
Tiger, Georgia USA
http://www.rabun.net/~leswatts/wattsfurniturewp.html
engineering page:
http://www.rabun.net/~leswatts/shop.html