From: Charles Oliveri 
To: atm{at}shore.net
Reply-To: Charles Oliveri 


Hi Matt,

"Matthew L. Brown"  wrote:
 >1. I just finished grinding two 4.25" mirrors using 1"
tiles.  It worked
 >fine.  I decided to trim the tiles on the edge, but I think you might not
 >need to do it.

 >2. In these archives I've read of people doing mirrors as thin as
 >18:1.  Your mirror would be 17:1, so I suppose that qualifies.  Note that
 >relative stiffness goes UP as things get smaller, so that's in your favor.

I'll give the tile tool a try. I don't envision a major problem at
conservative f ratios, but I'm hoping to get one blank down to f/4. I seem
to recall stumbling across the web page of someone doing a 4.25 or 4.5 inch
newt for solar observing out of either 1/4 or 1/3 inch glass a year or so
ago. Never was able to find the link again, and don't remember the f ratio
used.

 >3. You would probably want to grind the back side of the mirror blank with
 >#320 or #500 to prevent distracting reflections during figuring.

Yep, sounds reasonable...

 >4. The nice thing about little mirrors is they go quickly.  I've learned an
 >awful lot working these two  little mirrors.  The converse is you have to
 >have a light touch figuring.  Things went much better for me when I
 >switched to rouge.  With cerium oxide I kept overshooting.

I don't have any rouge on hand. I will try submerged figuring on the small
blank with a dilute cerox slurry to slow down glass removal. I'll gladly
sacrifice speed for control. And being that this is a learning exercise....

 >5. Before you start, you probably want to check for residual stress.

Thanks for the info,
Charles

--- BBBS/NT v4.00 MP