Re: ATM:Oversized Lap Not Removing TDE

["Bill T." <twentiethwave@hotmail.com>]

Hi Bill,

There are two important things on my setup:

1. There is a lot of surface loading on the mirror.  It's about equivalent
to the loading due to a 5" thick blank by itself, something around 6 ounces
per square inch.

2. The net effect of the oversized aluminum mirror carrier disc, and the way
it cradles the mirror between the four pieces of hardwood, is that the
mirror is effectively pushed from the back.  My impression is that the
trailing edge of the mirror is usually pushed very minutely down towards the
lap, and the leading edge is riding minutely high.  It's really just a
slight difference in loading.  I see subtle evidence of this in the way the
CerOx spreads around and sometimes in pressure patterns on the pitch.  This
may have a lot to do with the edge effects I mentioned on my earlier post.
It may also be the reason this machine yields such a clean edge -- it tends
not to dig the leading edge into the pitch, the cause of Demon Rolled Edge.
Please don't think I planned it that way...

In regards to manually rousting the mirror around, I have noticed that if I
grab the aluminum carrier disc it's MUCH easier to push the mirror and disc
together than it is to directly push just the mirror by itself.   A little
bit of handhold helps a lot.  It's a dramatic difference!  The technique is
worthy of investigation in its own right.   Here's that picture again:

http://www.kupercontrols.com/misc/20top23.jpg

You might consider putting a large diameter wood disc between the mirror and
a weight, to give you something to hold on to.  Keep an eye out on the tilt.
Has anybody tried this?  Oops... I see that you already thought of this!

A minor issue is that I use a little bit of dish detergent (about 1 drop /
500ml) in the Cerox so I can froth the Cerox mix into the channels with a
brush before starting.  Vigorous polishing maintains the froth for up to 30
minutes without having to add more liquid.  The pitch surface stays
consistently wet all over, even when the edges are exposed for long periods.
I wonder if you are experiencing drying towards the edge, or some other
surface wetting problem.  Pick up the mirror once in a while to see what's
going on there.

http://www.kupercontrols.com/misc/froth.jpg

Wish I could offer more specific help.  This is all new to me, too!  I just
lucked into a scheme that worked fairly well more or less right away.  It is
rarely so.

Bill Tondreau














----- Original Message -----
From: Wm. D. Hanagan, Jr. <hanaganw@attglobal.net>
To: Frank Ward <thewards@mindspring.com>
Cc: <ATM@Shore.net>
Sent: Thursday, March 15, 2001 5:54 PM
Subject: Re: ATM:Oversized Lap Not Removing TDE


>
> Frank Ward wrote:
> >
> > Bill,
> >
> > You want the driving force to move the mirror and tool over
> > each other, but the polishing force is downward. Plowing is
> > exerting that force on the side of the mirror which when using
> > an oversized lap will definitely plow the edge into the softer
> > pitch and give a TDE as a result.
> >
> > What size is your mirror? Didn't you say 8"?
> >
>
> Hi Frank,
>
> My mirror is an 8".
>
> How large of a mirror do you weigh down with 20-30 lbs of barbell weights?
>
> I'm beginning to wonder whether the high force required to drive the
mirror back
> and forth over the lap is forcing me into a bad hand position.  To apply a
lot
> of force to move the mirror, the heels of my hands must be partly pushing
> against the sides of the mirror.  To be sure that the mirror doesn't break
loose
> and crash on the floor, my fingers must also lay slightly over the sides
> of the mirror.  Those two requirements force my hands to the sides of the
mirror
> perpindicular to the direction of my stroke.  As I stroke back and forth,
some
> of the force I apply to the mirror gets translated into force pushing the
mirror
> into the lap.  Since my hands of necessity are straddling the left and
right
> sides of the mirror as I stroke, the edges of the mirror beneath my hands
could
> be experiencing greater pressure than the rest of the mirror.  In addition
to
> that, I believe the leading of the mirror experiences additional pressure
owing
> to the leverage affect that I mentioned earlier.
>
> It looks like I may need to REDUCE the force required to polish the mirror
so I
> can go back to putting my hands on top of the mirror like I did during the
> grinding stages and also cut back on the leverage that increases the
pressure on
> the leading edge of the mirror.  That, of course, presents a dilemna,
since
> reducing the driving force, whether by adding soap or lathering on the
polishing
> agent, has been widely reported to reduce the rate of polishing.
>
> An alternative I'm working on is a sort of frame to lay over the mirror so
that
> it can't be pushed off of the lap and so that the downward force applied
will be
> more uniformly distributed over the mirror.  Surely, though, this is a
problem
> others have fought and conquered.  How did they do it?
>
>
> Thanks for your response.
>
> Clear Skies,
>
> Bill
>
>