Re: [ATM] 12 x 12 tile tools?

["David Harbour" <scarab2@cox.net>]

In 1988 I made my first "superplanetary" telescope; when I ground and 
figured (yes, I polished before I figured) the 12.5" f/8 mirror, I used a 
laminated 12" X 12" tile tool substrate, ground the four 1/4" glazed terra 
cotta tiles together (to reduce the waviness on the glazed side to flat- 
removed the glaze, with 60 grit) so that when I epoxied them together (yes; 
I had a lapidarist friend nip the corners until the little straight edges 
where he nipped them came close to the circle I drew on the tiles to guide 
him to sawing it approximately round) they would be in better contact, more 
securely epoxied together. Then, I faced the laminated terra cotta 12" 
circular substrate with Winburn hexes, waxed the 3/32" wide channels, 
excavated the very top surface of the wax to approximately 1/32" below the 
level of the hexes, and ground out my f/8 12.5" with no trouble. I retiled 
the laminated floor tile substrate with a new layer of tiles before I got 
out of the 80 grit, and the whole experience was a trouble free delight. 
This was the second mirror I made, and it delivered awesome images on its 
big fork mounting, designed to carry up to 20" optics.

See my article here about why the wax is very beneficial, in the channels:

http://www.atmsite.org/contrib/Harbour/Tool.html

Here in my home town, there is a new tile vendor, retailer, and I noticed 
that he has terra cotta floor (patio?) tiles, unglazed, one inch thick, up 
to 20" diameter. Also, he has some very nice unglazed cushion edge one inch 
diameter hexes; they make a more efficient grinding face then the square 
tiles. But think of it: they have one inch thick by 20" diameter terra cotta 
patio tiles! One could laminate two of them together, after nipping them 
round with a lapidarists' saw (I have a friend who has one of these, and 
will do this for me), and face them with the pretty little hexes, and have a 
full sized tool that was very dimensionally stable, and have a wonderful 
experience hogging a 20" mirror out with a full sized, relatively easy to 
handle 20" tool. Subdiameter tool for hogging out is of course easier and 
more efficient, but there is the tiniest bit of extra risk in getting an 
ellipsoidal curve (astigmatism) than with a nice full sized tool.

If any of you guys need hexes, or big terra cotta floor tiles to laminate 
together for tools, I would be happy to act as agent for you, go out, make 
sure that I inspected the goods before shipping purchasing for you, and send 
you what you need. Let me know.

Davey

Winburn, out of Little Rock, Arkansas- the brand that Willman Bell used to 
sell, went out of business- but there is another fine, one inch diameter, 
"cushion edge" unglazed hex available, right here. They look almost 
identical to the very fine Winburn tiles; however, they do not have the 
cushion edge near the rim on both sides, but only one. But, that's even 
better!


----- Original Message ----- 
From: "Guy Brandenburg" <gfbrandenburg@yahoo.com>
To: <atm@atmlist.net>
Sent: Thursday, March 09, 2006 5:01 AM
Subject: [ATM] 12 x 12 tile tools?


>I will pass along a query from a friend:
>
> "I was wondering why people use 1x1" ceramic tiles for
> the mirror tool, I was wondering if you could use a
> 12"x12" tile and nibble it into a circle and make a
> tile tool out of that.
> "Do you think that would work?":
>
> Guy
>
>
> Guy  Brandenburg
> Washington, DC
> My home page:
> http://home.earthlink.net/~gfbranden/GFB_Home_Page.html
> _______________________________________________
> ATM mailing list http://www.atmlist.net/
> 


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