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The S&T Article

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Posted by Rick Crockett on October 2, 2000 17:35:26 UTC

Since the original post, I have had the opportunity to read the article.

If you will note, it is much more than just a simple bolt. The article puts a limit of eight inches for using a bolt. Then the system progresses to an annular pulled ring and finally to a system I believe I suggest here about a year ago. That is a foam backed mounting plate to distribute the force more evenly. It also becomes necessary to grind a curve on the back about equal to the one on the front which makes sense as the resistance to the pull would be disproportionally higher at the otherwise thicker edge.

Other considerations. At the same time I mentioned using foam I said that there may be a problem with cooling so I mentioned using RTV Silicone which would allow the back to cool better than the foam. Ah but RTV may also draw against the back and introduce its own distortions. Then there is the support. For a 10:1 we start thinking of going from 9-point to a 12 or 18 or even 27 point. What is this system going to do and over time?

I encourage experimenting but you should learn to produce parabolas first. Long before you can finish this mirror this way, I can have a parabola of twice the size in service. It is my concern that some of you will try this as your first mirror and that it will not be what you hoped and get discouraged. Also some of you may have made a mirror and found that getting a good figure can be difficult. The point I make is that if you null test, it is really no harder to get a good paraboloid as it is to get a good sphere. Many times individuals arrive at a sphere, but it is not a good sphere, they then proceed on to a lumpy and misfigured paraboloid while totally overwhelmed by the process.

Have Fun,
-Rick

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