tips on how to machine a large arc

Choiliefan said:
^^ Fred who, Colvin? ^^
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Fred was my first and only employer in the trade. He was my mentor, he taught me the trade and the business. He allowed me to promote myself to shop foreman, draftsman, purchasing agent and IT tech. When he no longer required my services, he arranged a loan so that I could take some of his best employees and go into business for myself. More recently, he gave me a nearly complete machine shop so that I could do that which drew me to machining originally, make cool sh*t for myself.

I owe all that I have and all that I am to Fred.
 
I have heard of a diamond disk in a tilted head mill being used to hog out a mirro to the correct radius of curvature.
At the time I thought it was an excellent idea but I've been unable to find it again after 4 days of searching.
I will cheat and swing a diamond disk on a pendulum over the spinning blank.
 
I wouldn't bother with my rotary table. I'd figure out my depths using a spreadsheet and using a 1/4" cutter cut the exact depths by stepping down in the centre... There would only be a small amount to take off with the sander. Much more accurate that doing the whole thing freehand and only cutting to the layout...

p.s. the lowest point the cut is slightly under .180 (i.e. the centre)

10 minutes in the spreadsheet, and 10 minutes on the mill., and easily 15 minutes on the sander.

-Because a telescope is only 'nominal' dimensions, I'd then use chalk like bluing compound, and hand finish it to fit.
 
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