From: "mlbrown{at}everstrive.com" 
To: atm{at}shore.net
Reply-To: "mlbrown{at}everstrive.com" 


The website was aimed at both my young nephew and his college educated
father, so it is a bit didactic.

I couldn't find a good layout of 1" tiles that had enough coverage for
a 4.25" mirror.  Four tiles across was too centered. You end up with a
3x3 square, and it really didn't look like it covered well enough.  But for
a 6" mirror, you can get 5 across, and that covers just fine.

You ARE correct about not having tiles extend over the dental stone.  All
in all, it was a nice experiment, and I'm totally sold on the tile idea.

Prices are higher here in N. California, and I did pay for the convenience
of picking it up from a nearby dental supplier.  Some day we should all
write the reactions from the suppliers when they ask what you are going to
do with it.  They were very careful to insure that I wasn't setting up my
own dentistry shop, and for some reason, my explanation of mirror grinding
didn't work well.

I didn't indicate that in subsequent tools (of course, I made separate
tools for the pitch laps) I realized that you can use the dental stone just
about right away.  I think I poured my lap about 20 minutes after I started
pouring the dental stone.  And all of the dental stone tools have held up
well -- no delamination at all.


Back to the original question: would hard porcelain tiles work?  Yes, if
they are hard all the way thru.  Many tiles just have a hard glaze over a
soft underbelly.  The glaze grinds away, and the soft part won't support
grinding.  In my newbie opinion, you can use just about anything that's
hard enough and won't shed glass-scratching particles bigger than the grit
you are grinding with.

That's the neat thing about this hobby of ours: there are lots of good ways
to make a telescope and its parts, most of which work pretty darn well
(especially Richard's mirror clips, as long as you clamp them down tight)
Just look at all the spider/diagonal holder designs: wires, hacksaw blades,
shipping container straps, even a piece of stout bendable wire I saw on a
little 3" scope.

=Matt


Original Message:
-----------------
From: Bob May bobmay{at}nethere.com
Date: Wed, 12 Mar 2003 11:07:20 -0800
To: mlbrown{at}everstrive.com
Subject: Re: ATM tool options


Looked at your website a bit and thought the 4" mirror article quite
nice. I do notice that you fell into the trap of having to make the tiles
go all the way to the edge of the tool.  You should mention in the article
that you want the tiles fully enclosed by the dental stone rather than hang
over the edge of the tool.  I also have the tiles to be at least 1/.2 of
the original size so that they will hold well.  The dental stone doesn't
make for any problems with the grinding and will very nicely accept a sharp
edge without damaging the mirror during grinding. I will also note that the
price you paid for the dental stone was a bit high as the stuff can be
found on the web for about $16 on the web although shipping will drive that
price up a bit.  I'll also note on your next tool that you can start
working with the tool about 1/2 hour after you get the stuff mixed up -
this is what I do with the guys in the mirrormaking group. Bob May
http://nav.to/bobmay
bobmay{at}nethere.com
NEW! http://bobmay.astronomy.net




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