[ATM] mirror pinching

[Mircea Pteancu <mirceapte@yahoo.com>]

Hello everybody
  I'm lurking (in silence) on this list since last Augustbut now I need advice.I intend to rebuild my telescope,a Dobsonian of  160 mm aperture F/9  and I'm looking for advice for the primary cell.The plate glass mirror is a "problem mirror" becouse the back is convex and  the rim is conical ,the diameter of the back is a few millimeter smaller than the face of the mirror.The original cell is a nine point flotation cell with three laterall support.I believe the mirror is pinched by lateral support.
  The thickness of the mirror is of 16mm, so the ratio is 1/10.
  After all the readings on this list ,I am thinking about  a six point PLOP cell , RTV glueing the mirror to the "points",avoiding the need for laterall support.But mirror pinching is coming back.
  Wich pinching is wors,the one from laterall support or that due to RTV glueing? I can avoid in some other way pinching of the mirror?
  Regards,Mircea

       
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