From: "Bob May" 
To: "Michael Lindner" , 
Reply-To: "Bob May" 


There is a way of doing a linkage on a lathe that connects to the slide
that will turn the radius desired.  The design is fairly accurate as you
can repeat the work as long as the joints are tight but setting one up can
be an exercise in frustration if you want a very particular radius. The
other easy method is to just use a full length radius rod with the lathe
again and that can be measured a lot more accurately but you may need to
have a long distance from the lathe to the pivoting end of the rod to make
it work.
I'll also note that even cast iron wears as you grind so you will need to
keep track of the ROC if you are trying to do a production of a number of
mirrors and adjust the points at which you are grinding to keep it
spherical and of the right radius.

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