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Originally Posted by bojan
Why don't you use old record player as rotating plate?
I was experimenting with such "out-of-the-square-box"ideas a lot in the past.
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Basically because of it's limitations with speed control. I'm thinking of spinning an 80cm one next - that needs to spin very slow....
Quote:
Originally Posted by bojan
Including chamber with lower air pressure behind the thin membrane (mylar).. or high electrical field even.. concept always worked, but that was all.
At the end, you will find that there is a reason why glass is used for mirrors... It is because only glass can keep the shape within required tolerances (1/10 of the wavelength) over wide temperature range etc, while it is reasonably easy to figure it precisely enough [speculum (used in the past for mirrors) is another example of good material... but obviously not as good as glass, otherwise it would have been used already]
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Hmm, always wondered about the Mylar - saves me trying that! :-)
I was also thinking about coating the final spun cast with a harder layer for final figuring and coating. Perhaps even like the process of case-hardening metals - increasing the carbon content of the outer millimeter or so...most likely impossible without an electrostatic coating method, and/or heating to impregnate the harder substance into the surface for finishing...
Quote:
Originally Posted by bojan
Even with glass, if the mirror is not mounted properly, things can go wrong (in optical sense - mirror pinching is notorious, for example.. temperature gradients inside the glass are more subtle but still significant).
This method may be useful though, to obtain the initial shape of the glass for grinding - polishing. I imagine it is used for manufacturing large mirror blanks....
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Hmm, be good if you could build a spinning mould that formed part of a plasma chamber, filled with argon or similar, that melted silica sand in the mould. Saves having a huge oven with high-temperature drives, etc...
Hmm, temperature consistency, etc...