Saturday, July 13, 2013


130709 SBAU Telescope Workshop July, 10, 2013 [notes by TimC]
Attendees:  TimC, DmitriiZ, JerryW, EdK
TimC - I brought my 16" to start up my grinding of 220 grit. What I noticed is I had some 220 Silicon Carbide and my own stash of 220 grit but it was Aluminum Oxide. My question to the group was, " Is there a difference in using Silicon Carbide to using Aluminum oxide?" The general answer was maybe there is a difference in the "hardness of the silicon carbide to aluminum oxide". ( I believe that is exactly right ). So, we decided to use up the Silicon dioxide before using the aluminum oxide so we don't introduce different tumbling and wearing factors of the medium.
DZ - Dmitrii brought his laptop and showed us what he is planning for the Tinkerer's Fair. We want to contact the group of the AU and ask if it is possible to use the new monitor. (A huge concern). We are okay with re- boxing it after we use it so we don't offfend the office of Javier. He is simply concerned with storage- and he is right- we should respect his space. We would be glad to re-box it and store it away. (Unfortunately in his office). Dmitrii will loop 3 videos and some photos to show the public what we do in the telescope workshop. But moreover, we are showing the public what it is like to build a telescope by grinding, testing and cleaning optics for use in the field.
JW -  Jerry talked a bit about Pat's unfortunate accident. She is doing just fine. I am not sure if anyone has met his spouse Pat, but she is just about as fine a match for Jerry as you would expect if you had to pick the perfect couple. They are just elegant in every way! But aside from that, they are just easy going and easy to talk to. I wish more people were like them.  I think Jerry is going to bring a scope to the Festival or Fair. I am thinking now of asking him to bring a Cassagrain he made. It is an example of a different type of scope from the traditional Newtonian.
EK - Ed Kalasky will be a free floater the day of the Fair. It is becoming apparent we need to have a couple of free floaters to do the work in between all the action of the day. I will explain this I hope in an up coming email.

Wednesday, July 3, 2013


130702 Telescope Workshop meeting minutes July 2, 2013
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: )
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: describing grit numbers, etc.]
 --Discussing Tinkers Fest, July 21:
-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: