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Re: [ATM] mirror grinding
Bob,
I am ashamed to say that I haven't a clear notion of this thread. I went
back and checked the previous posts, and am embarassed to tell you that I do
not understand a coule of things; I'll bet you can explain them with an
economy of words. When I was essentially teaching myself how to use tile
tools ("channeled" tools) for my first mirror that I was going to use (12.5"
f/8 for Moon and planets) I made a flat tool to start with, using Winburn 1"
hex tiles; I would have used the 2" tiles, except I knew I would have to
re-tile at some point (I did: the edge tiles got MIGHTY thin) and I knew
that the one inch tiles would come to curve quicker.
Now, I did re-tile, with epoxy and one inch Winburn hexes; I used two tube
clear epoxy resin and hardener. Here is my question: what would have been
the matter with me just epoxying on TWO LAYERS OF TILES to begin with; same
number of tiles, same (actually, a little less) labor; i.e., you mentioned
economy. Same number of tiles, same amount of labor. My substrate was a four
layer sandwich of Terra Cotta glazed 12" floor tiles (usually they will give
you four or five for free, "samples", to help you decide what kind of
kitchen or bathroom tiles you will want at the tile company). I had a
lapidarist zip them nearly round in a few minutes (using dangerous PVC as a
lubricant for his cutting wheel; I'll probably croak of PVC poisoning-
probably what's the matter with my head now!).
Now, I am embarassed to admit this to you (even after reading previous posts
to this thread: what is this "hole" you are talking about? My tools never
had a "hole" in them; even my largest. What is this hole you are referring
to? What is its form and what is its function? My laargest tool was a
Porland cement/Winburn Hex tool; worked like a dream. Wish I still had it as
a souvenir. Got away from me, like everything does.
http://www.atmsite.org/contrib/Harbour/Tool.html (This article is for
making tools for curve generated mirrors only- many basics apply for a flat
one, though. I have an article for a flat one on my machine.
I never used a new substrate; I just re-tiled with two tube epoxy cement.
What I really wanted to do was to have the cojones to try my radical plan of
a tile tool made this way: six or seven Terra Cotta (with Terra Cotta floor
tiles ground flat first of with 40 grit) epoxied together for substrate,
and then pave the grinding face, waxed and excavated as per correct
practice, with three or four layers of two inch diameter Winburn Hexes
"stacked" for the grinding face. I hope I have posed my questions clearly
enough for you, Bob, BECAUSE I KNOW THAT Y0U HAVE THE RIGHT ANSWERS: YOU
ALWAYS DO. Just don't understand the hole thing, or why anyone has to use
more than one piece of glass (or any piece of glass) for the substrate tool,
when you can get these 12 and 13 inch Terra Cotta floor tiles. Straighten me
out, Master.
I don't know how many have ever used three or four 12.5" Terra Cotta tile
tools as a substrate- pretty neat- nearly as dimensionally stable as glass,
and usually- FREE.
Dave
P.S. tell me about this hole, Bob.
----- Original Message -----
From: "Bob May" <bobmay@nethere.com>
To: <atm@atmlist.net>
Sent: Tuesday, June 28, 2005 1:13 PM
Subject: Re: [ATM] mirror grinding
> ----- Original Message -----
> From: David Harbour <scarab2@cox.net>
> To: ATM List <atm@atmlist.net>; Bob May <bobmay@nethere.com>
> Sent: Tuesday, June 28, 2005 6:15 AM
> Subject: Re: [ATM] mirror grinding
>
>
> > Bob-
> >
> > I have often thought about this: why couldn't a guy, who knew he was
going
> > to do a deep (fast) large mirror, start with a flat tiled, channeled
tool,
> > with say, three or four layers of tiles epoxied on at first! THEN HE
> > WOULDN'T HAVE TO RE-TILE!!!! HAS ANYONE EVER THOUGHT OF THAT?
> > Dave in Oklahoma (oops! "Okrahoma")
> >
> > Thanks, Bob-
> > Dave
> >
> Cost! Why spend money when you don't have to! The idea behind tile tools
> is to drop the cost of making a mirror by replacing the expensive piece of
> glass to be used as a tool with plaster and tile and a cheap piece of
metal
> for digging the basic hole that ends up being less than 10% of the cost of
> that glass.
> Bob May
> bobmay@nethere.com
> http://nav.to/bobmay
> http://bobmay.astronomy.net
>
>
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