Well there you go! I didn't believe it could be so easy to grind a circle out of 19mm glass but it went like a dream. I now have a circle of 6" diameter by 19mm thick and it only cost me $24 for the glass and about $10 for a piece of pipe and bits of flat steel. Much cheaper than the $115 quoted from the glass shop.

I have also used one of the trial circles cut out of 6mm glass and glued it onto a piece of 1/2" ply for my grinding tool.

I am thinking of making a 6" F5 primary mirror and have worked out a focal length for the tube of 30" with a sagitta of .075 thou.

Is this correct and what size secondary mirror do i need? Also is the secondary mirror flat and oval? I have done some trials of 1 1/2" by 2 1/4"
and 2" by 3" ovals and these look ok with the view of the base in the tube in the scope of the mirror.

So far things have worked out a lot easier than i first thought and have given me renewed faith in trying the grinding process.

So here goes!!!!!

• 6" - bobmay - August 25, 2002 - 19:55 UTC
  • 6" f/5 primary questions: - lachrimae - October 8, 2002 - 16:37 UTC