From: Gerald Boutin 
To: atm{at}shore.net
Cc: "'Thomas A. Moulton'" 
Reply-To: Gerald Boutin 


Tom, that is an interesting point you bring up. The short answer is yes and no.

My problem now is chasing after a pit that has been around since 320 grit.
However in the course of 50+ wets, I have seen pits that I was chasing
disappear with new baddies popping up in other spots.

Mind you, my nemesis pit has "morphed" as I have been chasing it.
At the end of 320 grit, it didn't look too bad and I actually thought I was
getting rid of it. However, it seems to have released a fracture from below
and I am left with a .006 inch triangular divot in my mirror surface. This
probably points to an earlier error that may be still haunting me.

I never did totally clean up the surface of the convex disk of mould marks
when I first started coarse grinding. Of course, that would not be an issue
if I was only dealing with the concave blank. After I started actually
looking at the mirror surface with a 10X magnifier at the end of 120 grit,
I noticed that the center of the convex disk had a lot of what I call
"chicken tracks" which I believe are probably what's left over
from the mould marks. At the time, they only appeared to be extremely
shallow indentations and I kept thinking they would disappear with the next
wet. However, they proved to be more stubborn than I expected and this last
one is still with me.

I have done numerous sharpie tests and I can get rid of ink with no
problems. Likewise, I am convinced that these disks are pretty spherical
and well mated as it has been a long time since I last had any hints of
stickiness.

I do not want to go to 12 micron yet as if I can't get rid of this pit
using 500 grit, I can't imagine getting rid of it with finer grit. I am
pretty certain it is not yet time to move ahead.

I still have quite a bit of patience left, but now would sure seem to be a
good time to make sure that I am grinding as efficiently as I can, so
that's what I am looking for advice on.

--
Gerald Boutin

> -----Original Message-----
> From: Thomas A. Moulton
> [mailto:tom-dated-1056654449.2fcf74{at}moulton.us]
> Sent: June 21, 2003 2:03 PM
> To: Gerald Boutin
> Subject: Re: ATM Grinding Efficiency
>
>
> Are the pits you are seeing moving around of are you
> fighting to get rid of the same pits?
>
> Let the glass dry and mark the pits with a Sharpie
> (let it dry) and then do a single wet
>
> Look at the pits before and after the wet, are the pits
> filled with ink or are they fresh?
>
> If they are fresh then you are done, move to the next grit.
>
> tom
> ----- Original Message -----
> From: "Gerald Boutin" 
> To: 
> Sent: Saturday, June 21, 2003 1:45 PM
> Subject: ATM Grinding Efficiency
>
>
> >
> > Hi, I am into my first glass pushing project and I have
> bogged down at
> > fine grinding at 500 grit. I have done a lot of reading and
> made a lot
> > of mistakes along the way, so I know I am making some progress.
> >
> > I am working on a Wilbell set of 8 inch pyrex blanks using
> the materials
> > in their kit. I fully expected to be quite inefficient
> throughout the
> > steps but I cannot figure out why I am having such a hard
> time getting
> > rid of my last pits at 500 grit. I would like to improve my grinding
> > efficiency, before I run out of 500 grit. The earlier grit
> sizes seemed
> > to go more or less how I expected, which was about twice as
> many wets as
> > I have read would be considered normal.
> >
> > For 500 grit, I am doing wets of about 7 to 8 minutes of
> grinding 1/3
> > COC, no additional pressure and about one stroke per
> second. I generally
> > alternate the disks with each new wet. I am pretty sure
> that one of my
> > earlier errors was having reduced the amount of grit
> between grit sizes
> > too much. I started SiC 500 grit using 1/8 tsp of grit per
> wet. I am now
> > using closer to 1/4 tsp per wet. However, progress still seems much
> > slower than it should be, or I would like it to be.
> >
> > As confirmation, how can I determine what the optimum
> amount of grit is?
> > When using 1/8 tsp per wet, I never had any spillovers. Now, I am
> > getting about 3 to 6 spills over the edge of the bottom
> blank. Is this
> > about right?
> >
> > Likewise, how do I judge how much water is about right? I
> am generally
> > going for enough water to get more or less a thin slurry about the
> > consistency of milk. While grinding, I add a few drops of water if I
> > notice that I no longer see water receding as the top blank
> uncovers the
> > lower blank. (I may not have worded this last bit
> correctly, hopefully
> > it conveys some meaningful info.)
> >
> > As further information as to my present status, I am up to
> over 50 wets
> > of 500 grit, which works out to about 6.5 hours of actual
> grinding. The
> > concave blank has been pit free for the past 6 or so wets.
> I use a 10X
> > loupe and backlighting. However, I still have a couple more
> sizable pits
> > on the convex blank, the worst of which is near the center.
> My ultimate
> > goal is to produce a hyperbolic secondary, so it this blank
> that I need
> > to be pit-free. This pit is a triangular divot about .006
> inches on a
> > side and (I think) about .001 inches deep at one end.
> >
> > I have tried doing the last session of 5 wets using the
> concave blank on
> > the bottom as it seems to me that the other way around
> isn't going to
> > work the top of the convex blank where the pit is.
> Unfortunately, this
> > is taking the ROC farther away from my intended target, rather than
> > nearer. Worst of all, I could not see any noticeable
> reduction in the
> > pit size.
> >
> > So, any tips on how I can improve my technique and get on to my next
> > challenges?
> >
> > --
> > Gerald Boutin
> >
> >
>

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