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Re: Wonderings On Spin Casting Parabolic Mirrors, Multiple Mirror Telescopes

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Posted by Cly/">Cly on November 19, 1999 05:04:57 UTC

: Spin casting is what Roger Angel is doing down in Tucson, Az. with glass. This merely puts an approximate shape on the glass which needs to be finished with grinding. : When spinning a mercury pan to get a decent optical surface, you need a lot more than a smooth motor. You have all kinds of problems with vibrations from the bearings and even trucks passing by on the freeway some distance away not to mention earthquakes almost anywhere in the world. You need to isolate the whole apparatus very well from the earth. then you need to do an excellent set of bearings that won't add vibrations to the system. Finally, you need a motor that's pretty constant with it's torque and just powerful enough to spin the rotating part. Please note that excess power goes into vibrations related to torque irregularities rather than spinning the mirror. The biggest problem that you're going to get is waves in your fluid from the vibrations. Viscous couplings will reduce the speed variations and will probably be needed.

: As far as multiple mirror telescopes are concerned, I did see one up at RTMC in the late '80s I think was made up of 6" mirrors. The guy was trying to align the system and not really having much success. I have no idea of the details of the scope and have no idea if the scope really worked at any point. I might also note that this was before the computer control of telescope mirror shape and position (not to be confused with active image tracking that's producing such good results with some of the larger professional mirrors).

Thanks for your response, Robert. Adaptive optics is WAY past my weekly allowance. Someday, though, I'm gonna try a 3 or 4 6" mirror scope. On spin casting, My wife won't let me cast molten glass in the garage (I think she's afraid I'll burn us down!), which is why I was thinking of a low temp media, plastic or epoxy, or the like, letting it cure while rotating. Maybe I should talk to Roger in Tucson for some insight. Thanks again.

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