[ATM] Cassegrain, primary mirror perforation size

[Otterstedt@t-online.de (Heiner Otterstedt)]

Hi everyone,

I'm on my way to finish rough grinding on my recent project, a 12" 
RC-Cassegrain. The next step will be drilling the central hole into the 
primary mirror, but I'm still a bit concerned about the diameter of that 
hole. So I would like to present my data for discussion. I used Michael 
Peck's spreadsheet ( 
http://home.earthlink.net/%7Emlpeck54/astro/cassbaff/ ) to calculate the 
baffles and got 89.66 mm at the primary baffle front. So I decided for a 
hole diameter of 97 mm (3.425") to be on the save side and get the 
baffle-tube through the hole. Are there any big mistakes in my 
calculations?

Unfortunately I do not possess Microsoft Excel, so I imported Michael's 
spreadsheet to my Google Docs account and filled in my data there. 
You'll find the public version at this location: 
http://spreadsheets.google.com/pub?key=pRtorKFeNCBuGObmdCxSgTg

My (german) grinding log is located in my workshop-blog at: 
http://hobby-werkstatt.blogspot.com/
Maybe the Yahoo Bablefish in the menu on the right hand side helps to 
translate it ;-)

Regards, Heiner
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