Re: [ATM] Figuring nightmare I need your help

["Scott Ewart" <scott.e@quicksurfer.com>]

Brent,
    It's hard to make any real progress with a 3-inch tool.  You're working
so little area at a time, it can take forever (but if you were really close
it would seem to chew right in and make it ugly).  You say you're running
the 10" tool 1.5" over the edge, but you really have to run it out almost
half way off (like at least 3 or 4" over-hang).  Just keep rotating the tool
and keep lots of weight over the mirror.  And always, always keep in mind
where you want to wear the glass and concentrate on keeping weight and the
fat part of the tool over that area..
    I think it may be possible to turn the edge (with very soft pitch) or
just to continue over-correcting this way, BUT I think you'll find it hard
to actually work the very edge more than the rest of the mirror.  More
likely, you'll find you really have to be out that far to wear the part of
the glass you need to.  I never turned an edge this way and even managed to
fix it after NOT working to the edge enough.
    Trust me.  I did a 12.5" with a 10" tool and I've been through it all.
DON'T BE AFRAID OF THE EDGE.  What do you have to lose at this point?
    If it's not too much trouble, you could make a full-sized tool, but you
should be able to get back under control this way.  And I like the idea of
pressing with cheese cloth.  You can use plastic screening, too.  That's
what I used.  But don't forget to press briefly without it before you start
stroking.  It cuts fast and usually leaves the surface surprisingly smooth.
But don't worry too much about smoothness right now.  There'll be plenty of
time for that later.

Scott Ewart


----- Original Message ----- 
From: "Brent Russell" <brussel@bpc.org.za>
To: <atm@atmlist.net>
Sent: Friday, October 01, 2004 11:40 AM
Subject: [ATM] Figuring nightmare I need your help


Hi folks,
I received no replies to my last message posted to the list. So I try
again
I am trying to figure a 12.5" plate glass mirror. Figure is mooth and
edge is good. I am using a 10" a 6" and a 3" tool.
The mirror is about 2.5 to 3 waves over corrected and I cannot no matter
how hard I try get the edge zones to flatten out. I am desperate here. I
am nearly at the point of re fine grinding. No matter what I do the edge
zones will just not respond to anything I do
I have tried 25 times round with the 3" on the high spot no change I
have tried chordal strokes with 6" tool just inside the high spot no
change I have tried 20 minutes with the 10" tool using a chordal stroke
with about 1.5" overhang - no change to the edge zone
HELP PLEASE :-0
Do I make a full sized lap
Do I re fine grind
Do I try different strokes

Regards,
Brent


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