TimC, TomW, JerryW(emerg. leave!), TomK, EdK, JoeD, TomT
TC- grinding 60grit on donated 8” mirror. As shown previously in this blog, Tim made new tool from old one and beveled edge on f/8 polished mirror pyrex. He is making it into a ~f/5.5 unit. TomW helped grind also. The grinding pattern used by Tim was chordal, while TomW was using the "W" pattern for center deepening (see: http://stellafane.org/tm/atm/mirror-refs/strokes.html )
Final surface tonight was an evenly ground glass surface. The excellent mating of the tile tool with the glass could be seen through the back of the glass. The sagitta (ground glass depth in the center) was measured against the desired depth calculated by TomW. The donated 8" mirror had a focal ratio of f8, with a sagitta depth of 1/16". The focal ratio f5.5 desired depth needs to be 3/32" (f5.5 x 8 = FL44" = RC88"; S = r^2 / 2 x RC = 4^2 / 2 x 88 = 16/179 = 0.091". [FL = focal length; RC = Radius of Curvature.] A penny (0.061" thick) fit almost perfectly beneath the straight-edge provided by Tim and a 1/16" drill bit (0.0625") was about the same. [Another little grinding a mirror website by an ATM: http://mysite.verizon.net/res6jv9o/astronomy-trains/id20.html describing grit numbers, etc.]
-TimC mentioning all the folks expected to attend and stuff to bring. TT will check on using 42" SBAU TV currently stored in Javier's office.
-TT, TW reviewed TimC 10 slide powerpoint (16 slides!)...he will send to Dmitrii by email, since less than 10MB in size.
-TK- 4.25 mirror blank grinding setup (see photo) for the Tinkers Fest looked at...TimC suggests doing grinding on a picnic type bench to enable sitting across from someone practicing the strokes.
TT- showed TomW Westmont mirror presentation at Summer Science Program Flickr photos to a few folks, after finding a wi-fi connection out at the bridge to download.
More discussed photos here: http://www.flickr.com/photos/27241501@N03/collections/72157623730631261/
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