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Adventures in Specialised Glass Machining

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Andre ROUSSEAU	02/05/2023 05:11:37
90 forum posts 1 photos	https://youtu.be/A0bysBIj0FA
John Haine	02/05/2023 08:59:45
5563 forum posts 322 photos	Andre, PLEASE could you learn how to post active links? It isn't hard.
Neil Wyatt	02/05/2023 16:22:49
19226 forum posts 749 photos 86 articles	youtu.be/A0bysBIj0FA and
duncan webster	02/05/2023 16:56:50
5307 forum posts 83 photos	And put some words telling us what it is. I don't click on random links, that's the route to scams
Nigel Graham 2	02/05/2023 17:14:19
3293 forum posts 112 photos	Link problems aside, that is very impressive - all the more so since the final grinding and polishing to optical standards is by hand! He doesn't say how long it took, but that must be hours of work with the patience and care of a neurosurgeon. One of Holtzappfel's books shows how large telescope mirrors and lenses were ground in the 19C by clamping a precision flat disc of glass down onto concentric rings of accurately-set jacks similar to toolmakers' ones, so curving the blank against its own elasticity. (New glass is very, very slightly flexible but it hardens and becomes more brittle with age, explaining why you cannot usually re-cut old windows.) The distorted blank was then ground flat, so when released it would rebound with a concave surface of the appropriate, very large radius.

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