Re: [ATM] Tool Tiles

["Bob May" <rmay@nethere.com>]

As to stability of the material, be careful of what is said in
this regard.  A house builder will consider it to be very stable
while some rocket scientist would consider it to be unstable as
it expands a little with temperature (as do most things) and even
with moisture.
Bob May

rmay at nethere.com
http: slash /nav.to slash bobmay
http: slash /bobmay dot astronomy.net

----- Original Message -----
From: David Harbour <stainless_steel@suddenlink.net>
To: <fundo@bellsouth.net>; Ron Gafron <rgafron@sbcglobal.net>;
'Bill Wheaton' <junkwheaton@gmail.com>; 'ATM list'
<atm@atmlist.net>
Sent: Sunday, May 18, 2008 6:10 PM
Subject: Re: [ATM] Tool Tiles


> Dan,
>
> Thanks for your input here; it is appreciated. What is the most
striking,
> (to me) is
> your comment about the dental stone possibly expanding over
time. I read a
> respected "authority" say, in print, that Dental Stone is not
DIMENSIONALLY
> STABLE OVER TIME.
>
> My previous proposition stands: look at a fifty, or 75  year
old concrete
> block; you can tell if it is an old one, becuase the old ones
were quite
> different in style from the current, nearly standardized
concrete block;
> then, examine your estimation of whether or not you think it
has changed,
> dimensionally, over those 75 years. That is why I used Portland
cement and
> sand.
>
> But, I am just as happy as a Lark, to stay in a minority about
the
> virtues/nonvirtues of dental stone and Portland cement. I am
just saying:
> the stuff worked wonderfully well for me, was not expensive,
and the tools
> (Ron Gafron just picked up my last one, with the big mirror; he
was quite
> impressed with the tool) worked well for me, and did not seem
at all heavy.
>
> Perhaps it is subversion to promote the abandonment of dental
stone as a
> substrate for large tile tools. Okay. I am a subversive. But I
do not demand
> that anyone follow my methods; I am just happy to suggest them,
as they
> worked so well for me. I made a lot of these tools, and never
scratched a
> mirror, never lost a grain of sand between mirror and tool.
Miracle? No.
> Secret? No.
>
> May all of you, and you Dan, have the wonderful experience of
never having
> to hear that horrible "skreak" of a rogue piece of grit of say,
about 80 or
> 120 grade, or even a piece of sand, or other foreign invader,
between your
> tool and precious glass. It only happened to me once, on my
first mirror;
> never again did I use a monolothic tool. Also- my tile tools
made to hog out
> with, rather than work an already curve generated mirror, had
large
> laminated Terra Cotta floor tiles, ground reasonabley flat
against each
> other, and sandwiched together (after my lapidarist friend
nipped them round
> with his lickety split tile saw) for a substrate for the nex
tiles, which
> were epoxied on, and then waxed. It goes without saying that I
went through
> all of the mirror work on each one of those hogging a flat
blank out very
> quickly, as clear epoxy resin and hardener is not dimensionally
stable over
> time- so I didn't give it any time!!!.
>
> Whatever works... freedom is what it is all about.
>
> R-101/
> Davey/
>
> ----- Original Message -----
> From: <fundo@bellsouth.net>
> To: "David Harbour" <stainless_steel@suddenlink.net>; "Ron
Gafron"
> <rgafron@sbcglobal.net>; "'Bill Wheaton'"
<junkwheaton@gmail.com>; "'ATM
> list'" <atm@atmlist.net>
> Sent: Sunday, May 18, 2008 2:06 PM
> Subject: Re: [ATM] Tool Tiles
>
>
> > --- Original message from "David Harbour"
> > <stainless_steel@suddenlink.net>: --------------
> >
> >> For all: one of you might have a brainstorm to help Ron with
his full
> >> thickness Corning blank, ultra silky smooth ground to about
f/4.71 (or
> >> f/4.771)- my memory is hazy here, as it is in other areas-
the plug is
> >> still
> >> blocked in place; the original "blocking material" is, as I
determined 20
> >> years ago, "blocking pitch". I excavated this stuff down a
little ways,
> >> and
> >> my dentist and I did a "dental surgery" on it, with dental
stone, and
> >> filled
> >> in most of the excavated area with this stuff, leaving only
a very
> >> shallow
> >> depression to fill with clear epoxy resin and hardener, and
shards of
> >> plate
> >> glass that I cut out with a glass cutter. This worked great
for
> >> regrinding
> >> the mirror from 60 grit down to 2 or 5 micron (I forget
which) alox; the
> >> last wet was a very long one, adding a few drops of water as
it would dry
> >> out; the result was an ultra silky smooth grind. That was 20
years ago.
> >> The
> >> problem now is that the epoxy resin, not stable over 20
years, has slowly
> >> shoved some of the shards of glass upwards by perhaps .008"
or so; so Ron
> >> cannot polish this baby, ready to polish otherwise, until he
solves the
> >> problem of those shards sticking up. It will ruin his lap,
wreaking havoc
> >> all over it. We need to figure out what to do, so he does
not have to go
> >> back to a coarser grit; this way, he can avoid any
possibility of getting
> >> a
> >> "rogue grit" from gouging the mirror (if he can just begin
polishing
> >> right
> >> away)- but he can't, until we can figure out how to either
make the
> >> filling
> >> material in the annular plug groove congruent with the rest
of the mirror
> >> surface (I don't see how we can do this). As a last ditch
"remedy", I
> >> believe the plug shoud be removed, along with the top
surface of the
> >> circular trepanning cut, with its out of place shards of
glass. He will,
> >> of
> >> course, have to place a relatively thick spacer over the now
empty
> >> perforation when making his lap;
> >
> > The epoxy may not be the culprit here; it may be the dental
stone, which
> > if memory serves, actually expands a bit as it cures.  Curing
in portland
> > cement and gypsum based products takes 20 years for all of
the bonding to
> > occur (its been a while since I had that course in concrete
construction
> > and the memory is fading, like Dave's <G>).  In any case, you
will not be
> > able to get the offending pieces perfectly aligned with the
adjacent
> > surface, but a few thous lower shouldn't be a problem.
> >
> > This may seem a bit drastic but I have shaved down knots in
wood with this
> > method.  It may work with glass as well.  I used a router
bit, but a metal
> > pin and abrasive should do the same job.   This will be
localized
> > grinding.
> >
> > Mask off the offending area as close to the edge as possible
with heavy
> > duty plastic tape, I'd use several layers.  Cover the entire
mirror with
> > plastic or tape.  Get 3M 375 (archival) packing tape if
possible....its
> > very water proof. Make a template out of 3/4" plywood big
enough to cover
> > the mirror.  Get a small variable speed router (or a variable
speed Dremel
> > and a base for it).  Put a guide bushing in the router base,
and make the
> > hole in the template big enough to get a square ended steel
pin to cover
> > all of the required area.  Mix up a potion of AlOx and water
and  place a
> > few drops on the area you need to grind down.  Put the router
on the
> > slowest speed possible and set the depth of the steel pin at
the surface
> > of the glass (make sure its on the highest offending piece).
Let the grit
> > be the difference in cutting depth.  Turn on the router and
work your way
> > around the hole in the template.
> >
> > It might help to champher the edge of the pin.  You could
build a dam
> > around the outer edge also.  In any case, you're not
concerened about the
> > center plaug, so if it is a bit rough, you could still
polish.
> >
> > *****-----
> > Dan F.
> > Memphis, TN
> >
>
>
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