From: martin.cibulski{at}t-online.de (Martin Cibulski)
To: 
Reply-To: martin.cibulski{at}t-online.de (Martin Cibulski)


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>From: "scottythefiddler" 
>Subject: Re: ATM tool for pitch lap...

>Out of curiousity, has anyone ever tried a sand and cement tool?    The
>dental stone is nice because the grain size is very small, and much =
less
>likely to cause bad scratches if any of it gets onto the mirror.  =
Another
>nice thing about dental stone, is that it is soft enough to carve with =
a
>knife.  I like cutting little chamfers on the back to ease the sharp =
edge.
>A concrete tool, with fine sand as an agregate it going to be very
>inexpensive, very stiff, and quite useful, if it can be sealed to =
contain
>any loose particles.  The 40 lb. sacks of premixed concrete that are so
>common at the lumberyards have a plasticizer in it, as well as a =
bonding
>agent.  Dental plaster is designed to release from the mold, and =
bonding to
>other items is not its' strong point.
> ...
>I have never tried a cement tool, but my curiousity is up.   Has =
anybody
>tried?   What size, how thick, and did you have any problems with it?

I used a concrete tool for fine grinding of my 14" mirror and one for
polishing. The sizes are:
Grinding tool: 34cm x 3cm
Polishing tool: 29cm x 4.5cm
They can be seen on my grinding machine:

http://martin.cibulski.bei.t-online.de/grinding_machine.htm

First I made a tile tool of dental plaster but this one has been broken. At
this time I was grinding with 220 grit so the surface had become almost
spherical.

Then I poured a concrete tool on the mirror and glued steel washers on it.
Because of the already spherical surface later all washers came in contact
to the mirror. I never put any more weight on it and the result was very
good.
When the concrete was cured I put it into the oven to remove the remaining
water from it. (I rised the temperture slowly in a few steps over 3 hours
to avoid cracking) I put epoxy onto the hot surface (130 celsius) and the
washers on the epoxy. From the heat the epoxy became more fluid so the
washers could come into it from their own weight and reach the concrete
surface. I put it into the oven again and the epoxy hardened very fast and
became stronger from the temperature.

I used a 'fat' concrete mixture with one part cement and two parts sand and
small gravel (up to 8mm size). I added some iron into the tool to make it
stronger.

When I do this again I would use less water. Ideally there is only the
minimum amount of water which is needed for the curing. Any more water will
result in small hollows in the concrete because it dousn't react with the
cement. But concrete is less fluid so pouring it might be difficult.

Best Regards,
Martin Cibulski


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>From:
"scottythefiddler" <scottythefiddler{at}cogeco.ca=">mailto:scottythefiddler{at}cogeco.ca">scottythefiddler{at}cogeco.ca=
>>Subject:=20
Re: ATM tool for pitch lap...>Out of curiousity,
has anyone = ever=20
tried a sand and cement tool?   
The>dental stone = is nice=20
because the grain size is very small, and much less>likely
to = cause bad=20
scratches if any of it gets onto the mirror. 
Another>nice = thing=20
about dental stone, is that it is soft enough to carve with=20
a>knife.  I like cutting little chamfers on the
back to ease =
the=20
sharp edge.>A concrete tool, with fine sand as an agregate
it = going to be=20
very>inexpensive, very stiff, and quite useful, if it can
be = sealed to=20
contain>any loose particles.  The 40 lb. sacks of
premixed = concrete=20
that are so>common at the lumberyards have a plasticizer
in it, = as well=20
as a bonding>agent.  Dental plaster is designed
to release = from the=20
mold, and bonding to>other items is not its' strong=20
point.>
...>I have = never tried a=20
cement tool, but my curiousity is up.   Has=20
anybody>tried?   What size, how thick,
and did you have = any=20
problems with it?I used a concrete tool for fine
grinding of my = 14"=20
mirror and one for
polishing. The sizes
are:
Grinding tool: 34cm x
3cm
Polishing tool: 29cm x =
4.5cm
They can be seen on
my grinding=20
machine:
 
http=">http://martin.cibulski.bei.t-online.de/grinding_machine.htm">http=
://martin.cibulski.bei.t-online.de/grinding_machine.htm
 
First I made a
tile tool of dental plaster but this one has been =
broken.
At this time I was grinding with 220 =
grit so the=20
surface had become
almost
spherical.
 
Then I poured a concrete tool on the =
mirror and=20
glued steel washers
on it. Because of the already
spherical =
surface=20
later all washers came
in contact to the mirror. I never put =
any more=20
weight on it and the
result was very
good.
When the concrete was cured I put it =
into the oven=20
to remove
the remaining water from it. (I rised=20
the temperture slowly in
a few steps over 3 hours to avoid=20
cracking)
I put epoxy onto the hot surface (130 =
celsius) and=20
the washers
on the epoxy. From the heat the epoxy =
became more=20
fluid so
the washers could come into it from =
their own=20
weight and reach
the concrete surface. I put it
into the =
oven again=20
and the epoxy
hardened very fast and became =
stronger from=20
the temperature.
 
I used a 'fat'
concrete mixture =
with one part=20
cement and two
parts sand and small gravel (up to 8mm =
size). I=20
added
some iron into the tool to make it=20
stronger.
 
When I do this again I would use less =
water.=20
Ideally
there is only the minimum amount of =
water which is=20
needed
for the curing. Any more water will =
result in=20
small
hollows in the concrete because it =
dousn't react=20
with the
cement. But concrete
is less fluid so pouring it might
be difficult.
 
Best Regards,
Martin Cibulski
 

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