From: Guy Brandenburg 
To: Ellen Mackenzie 
CC:  atm{at}shore.net
Reply-To: Guy Brandenburg 


We have just been donated a mirror-o-matic polishing machine, and we have
someone who is trying an insanely huge and thin mirror, by hand - a
16" f/5 mirror of plate glass from Dan Cassaro. He is using tiles over
concrete for the tool, and is (so far) doing it by hand, with the mirror on
top. I am tempted to have him use this machine, but I have absolutely no
experience in using it. I figured that if we/he used the machine, we would
have to bond a place in the center of the back of the mirror for the
turning arm to hook into while grinding and polishing. Is that correct? Are
the handles only needed while polishing?

By the way, I like burgundy pitch from Willmann-Bell. It's easy to change
the consistency if it ends up getting hard over time, by adding a bit of
turpentine, or boiling for a few minutes if it ends up being to hard for
your conditions. W-B also sells beeswax and rosin, but no walnut shells
AFAICR.

Guy Brandenburg

Ellen Mackenzie wrote:
> I have used burgundy pitch on machines for mirrors up to 24 inch diameter. I
> temper the pitch with beeswax, 10-15%.I found that unless I held the
> mirror(MOT)in my hands it is easy to develop an orange peel surface. By
> holding the mirror in your hands you can feel the force and determine
> quickly when the lap must be lubricated with rouge compound. For mirrors
> over 12 inches I found it necessary to bond handles to the back of the
> mirror with pitch so I could hold the mirror against the torque.
>       If you are set on trying to polish completely with the machine--hands
> off--then listen carefully for "singing" which creates
orange peel, from a
> dry lap.Patience is not only a virtue it is a necessity.
>
> -----Original Message-----
> From: owner-atm{at}shore.net [mailto:owner-atm{at}shore.net]On Behalf Of
> Michael Burr
> Sent: June 6, 2003 12:40 PM
> To: ATM list
> Subject: ATM Burgundy pitch/machine polishing
>
>
>
> Greetings:
>
> I'm about to place an order for pitch, and I am considering using Burgundy
> pitch instead of Gugolz, which in my experience seems to be inconsistent
> from can to can. I am polishing with a Mirror-o-Matic machine. I posted this
> question to the MOM list, but I thought I'd also ask the ATM list.
>
> Has anyone on the list used Burgundy pitch with their machine before? What
> grade (soft, medium or hard)? Did you mix anything with it -- i.e., beeswax,
> rosin, talc, ... walnut shell flour? (Seriously.)
>
> Also, Willman-Bell sells a "tempered" Burgundy pitch that
has rosin and
> beeswax in it. It's a bit more expensive, but they say it "flows accurately
> for normal focal length mirrors and flats and is consistent from package to
> package and year after year. This pitch is the favorite of thousands of ATMs
> and professionals."
>
> Would this tempered Burgundy pitch be appropriate for machine polishing? I'm
> guessing the source of the W-B pitch has arrived at a happy medium that its
> customers like, but it could be happy for hand polishing and very sad for
> the machine. It seems to me that the beeswax would offset the effects of the
> rosin, so what's the point of adding both?
>
>>From what I've read on the ATM list, burgundy pitch seems to be softer than
> Gugolz, but I'm guessing it also has inconsistency problems.
>
> Any thoughts welcome.
>
> Regards,
> MTB
>
>
>
>
>
>

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