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dave b
Post Laureate
Reged: 05/10/05
Posts: 3528
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Re: Thick mirrors
07/06/09 12:36 PM
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thanks for the info scott!
i ask about the bubbles because guys in the club have been casting mirrors (they use a pottery kiln with different controller). they have found that the bubbles hide grit (even when blasted out with a waterpik) and contaminate the next polish. please keep us posted on how mike deals with this problem as he gains more experience.
"high temperature form material" is usually just 50% pottery plaster/ 50% silica flour. mirror blanks have been cast in this material for at least 100 years, probably much longer. guys in our club are forming the flasks then milling out the mold/ribs on a CNC router made by shopbot.
the only finished Lookingglass cellular i ever saw had u-clips siliconed to the ribs with a PLOP spacing (generated as if it were a mono). i could not find the link, ill look later.
speaking of "where is the engineering?", remind the guys at dream cellular that when you double the thickness of a material it becomes 8x as stiff - not 2x as stiff.
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dave bonandrini
30" f/5.2 Dobsonian
President of GCAC
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