On Sat, 30 Mar 2013 11:26:22 -0700, "anorton"
wrote:


"Ed Huntress" wrote in message
.. .
On Sat, 30 Mar 2013 07:18:24 -0400, "Jim Wilkins"
wrote:

"PrecisionmachinisT" wrote in message
news:SsqdndCiuYHgtsvMnZ2dnUVZ_uWdnZ2d@scnresear ch.com...

"Ed Huntress" wrote in message
news On Fri, 29 Mar 2013 16:13:03 -0700, "PrecisionmachinisT"
wrote:

--even with single point diamond tooling, surface finish becomes a
big factor when it comes to accurately gaging workpiece diameter..

Keep in mind that master hard-drive disks and the production disks,
back when they were made this way, were single-point turned. No
grinding. We built lathes especially for turning them at Wasino --
and
they were all shipped to Singapore. sob


Still they were nowhere near to a mirror finish.

And those were flat.


Moore Special Tool built special turning machines for making
assymetrical lenses for the Defense Dept. They were all single-point
turned, although some of them (for shorter wavelengths of light)
were
polished.


I've watched a large aspherical Germanium front lens for a military
vehicle thermal imager being diamond-turned. The tool resembled a
brazed carbide bit. The finish it left looked mirror-smooth to me.
They use a wavelength about 10X longer than visible light and are less
sensitive to roughness.
jsw


Right. That's what Moore was making. (Thanks for correcting it to
aspherical, not assymetrical. Sheesh.)

--
Ed Huntress

I have designed many diamond-turned optical elements and helped one vendor
optimize their process for our optics. Moore and Precitech are the two main
competitors in this field. Single point diamond turning (SPDT) used to only
be good enough for infrared optics, but now they are being used for visible
and even UV optics. It only works well for certian materials of course. The
cutting tool tip is usually a tapered cylinder diamond with the larger base
polished and facing up to make the cutting edge. Their are different sizes
but the typical diameter is 1 mm. The cutting edge has to be perfectly
circular otherwise it causes form error when cutting a curved surface. I am
sure someone has studied the cutting process in great detail for all the
common materials, and I am not an expert in that, but I am pretty sure it is
very clean cutting with very little flow. Materials that can not easily be
polished like soft aluminum can easily be diamond turned.

They do not usually turn directly in aluminum though. For best results, an
aluminum substrate mirror might first be rough-turned on a standard CNC
lathe, then plated with about 10 microns of electroless nickel, and then
about half the nickel thickness or less is turned off in the SPDT process.
The nickel then has a vacuum coating applied for best reflectance. The
vendor I was working with had their own in-house nickel plating facility in
a clean room so they could keep out contamination and inclusions.

If you want to see specs that will blow you away, check out this spec sheet
for their low-end model (e.g. 16 picometer encoder resolution!)
http://www.precitech.com/wp-content/...Broch_spec.pdf

Wow. Cool stuff.

So, is Precitech what became of Pneumo Precision? I see they use a
granite bed, like Pneumo did. And they're in NH, which is where, if I
recall correctly after 34 years, Pneumo was.

'Same company? I wrote about Pneumo Precision back around 1980, and I
was talking with them and Moore to write a substantial article. But
Moore was all tied up in non-disclosures with the Defense Dept. at the
time.

--
Ed Huntress