Question concerning mirror making project

Hello, people of sci.astro.amateur,
I am working on an independent study project that involves making a
small telescopic mirror. The professor's idea is to turn the mirror
out of aluminum or perhaps stainless. We have access to CNC machinery
and can turn a parabola according to a formula within accuracy of
+/-.0005". The blank will be about 2" diameter. Then we would grind
and lap it, then platinum plate through deposition.
My question to the good people of this group is, does this sound
feasible? This project is not for looking at stars. It has to do with
creating special eyeglasses. Once finished, a small rectangular
section will be removed then embedded in the eyeglass lens. But I am
not here to debate the pros or cons of that part of it. It is the
mirror part I was looking for feed back on, or for leads about which
sources of information might be helpful.

Thank You,
-plh
--
I keep hitting "Esc" -- but I'm still here!
[if "123" is in email address, that is an anti-spam thing.]

What you describe probably would work, but why the platinum reflective
layer?

plh wrote:

Hello, people of sci.astro.amateur,
I am working on an independent study project that involves making a
small telescopic mirror. The professor's idea is to turn the mirror
out of aluminum or perhaps stainless. We have access to CNC machinery
and can turn a parabola according to a formula within accuracy of
+/-.0005". The blank will be about 2" diameter. Then we would grind
and lap it, then platinum plate through deposition.
My question to the good people of this group is, does this sound
feasible? This project is not for looking at stars. It has to do with
creating special eyeglasses. Once finished, a small rectangular
section will be removed then embedded in the eyeglass lens. But I am
not here to debate the pros or cons of that part of it. It is the
mirror part I was looking for feed back on, or for leads about which
sources of information might be helpful.

Thank You,
-plh

An aluminum surface is nearly impossible to polish to anywhere near the same
quality as a glass surface. What can be done is to deposit a few mils of
electroless nickel and then polish that. Stainless steel can take a
somewhat decent polish.

You do not mention how short the F.L is on this parabola or what the figure
error tolerance is. Polishing something that deviates strongly from a
sphere is very difficult while still keeping a good figure. Remember that
usually 50% of any optical design project is doing the tolerance analysis.

There are many vendors who can turn this kind of part to optical tolerances
with no need for further polishing (except for the most exacting
applications). Search for single-point diamond turning vendors. Netoptix
(http://www.corningnetoptix.com/) is one of the best but not necessarily the
cheapest. If you do choose to use single point turning, cut the blank to its
finished rectangular shape first, then turn it. Multiple blanks can be held
on a single spindle during turning.

I also have to ask why coat it with platinum? If you are looking for
durability, such mirrors are usually coated with rhodium which has much
better reflectance.

--
Adam Norton

Norton Engineered Optics

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"plh" wrote in message
...
Hello, people of sci.astro.amateur,
I am working on an independent study project that involves making a
small telescopic mirror. The professor's idea is to turn the mirror
out of aluminum or perhaps stainless. We have access to CNC machinery
and can turn a parabola according to a formula within accuracy of
+/-.0005". The blank will be about 2" diameter. Then we would grind
and lap it, then platinum plate through deposition.
My question to the good people of this group is, does this sound
feasible? This project is not for looking at stars. It has to do with
creating special eyeglasses. Once finished, a small rectangular
section will be removed then embedded in the eyeglass lens. But I am
not here to debate the pros or cons of that part of it. It is the
mirror part I was looking for feed back on, or for leads about which
sources of information might be helpful.

Thank You,
-plh
--
I keep hitting "Esc" -- but I'm still here!
[if "123" is in email address, that is an anti-spam thing.]

plh wrote:
Hello, people of sci.astro.amateur,
I am working on an independent study project that involves making a
small telescopic mirror. The professor's idea is to turn the mirror
out of aluminum or perhaps stainless. We have access to CNC machinery
and can turn a parabola according to a formula within accuracy of
+/-.0005". The blank will be about 2" diameter. Then we would grind
and lap it, then platinum plate through deposition.
My question to the good people of this group is, does this sound
feasible? This project is not for looking at stars. It has to do with
creating special eyeglasses. Once finished, a small rectangular
section will be removed then embedded in the eyeglass lens. But I am
not here to debate the pros or cons of that part of it. It is the
mirror part I was looking for feed back on, or for leads about which
sources of information might be helpful.

Thank You,
-plh

You gotta love it when professors reinvent the wheel for the Nth time.
Diamond turned freeform molds for eyeglasses are common in industry.
Companies such as Optical Electroforming specialize in this type of
work. http://www.opticalelectroforming.com...d/diamond.html
The molds are turned in electroless nickel and have an off the machine
form accuracy of about +/- 0.000001". The form of these molds does not
have to be rotationally symmetric, and in fact these machines are used
to produce torics, bifocals, and progressive prescriptions.

BTW, stainless cannot be diamond turned. The iron in steel has an
affinity for the carbon in the diamond tool.

--
jeff