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Old 27-03-2012, 03:45 PM
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sopticals (Stephen)
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Join Date: Jun 2010
Location: Oamaru, New Zealand.
Posts: 206
25mm Plate glass,

As I had heard of other ATMers, using 1" plate glass for mirror blanks, I contacted Sydney Glass Pty Ltd, in respect to the 25mm plate sheets, they currently have in stock.

I received the following reply:

We have got some 25mm clear float, but is so badly annealed it is impossible to cut it conventionally.

We use a waterjet and often supply panels of this to telescope enthusiasts.

(I was then provided with prices for the various sized discs I had enquired about-waterjet cut-edges look flat ground-no bevels).
(I also asked about cut sheets ie. Full sheet cut in half/quarter.)

The reply continued:

There is no point in providing you with "stock" glass because of the cutting problem. (end of reply).

I wont give the name of the correspondent.(Writer).

I agonized, over whether I should post this information, or not, but felt if not posted, many ATMers may fall into the trap, of trying to make a mirror, out of the above.

If one is going to use cheaper glass, glass by the Pilkington process, (float glass), is generally ok, if it comes from a reliable source. Good float, is relatively free from strain, has acceptable anneal, reasonably flat (usually within 4 to 5 waves of flat), and wedge free. (front/back parallel).

I feel sorry for those, who may have tried mirror making, and have failed, due to poor anneal, of the substrate they selected, as a blank.

Stephen.
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