Re: [ATM] Fixing Tom's oblate sphere

[Mike Lockwood <melockwo@uiuc.edu>]

Tom,

Polk, Tom wrote:
> ****I have not been using any pressure other than the slight downward
> pressure of my heel when working TOT. MOT the downward pressure is only
> enough to grip the glass with rubber coated gloves (finger tips only...
> boy what a work out for the forearms!).

OK, there is your problem.  You have to push down on the mirror/tool 
quite a bit to really get them in good contact.  You should be using 
all of your hand, not just the fingers.

On a smooth-backed tool/mirror, I get my palms damp and they stick to 
the back enough for me to push the mirror/tool around.  This is quite 
a bit of pressure, and it gets tiring after a while.

 > **** How much pressure should I apply?

We are probably talking 10-15lbs of downward force, possibly more at 
times.  Pressure is applied in the central part of the mirror/tool, 
and the "heel of the hand" pressure is a variation in WHERE that 
pressure is applied, to counteract the lap "plowing".  If your stroke 
motions are smooth and your arms will handle it, you can apply more 
pressure.  Every operator is different.

> **** No, but at the point where the friction is too great I break
> contact and recharge with CEO. Similar to a "wet" but no washing.

Good.

> ****Hmmm... I'm breaking contact... to uniformly apply CEO to glass or
> tool with a couple water sprays from spray bottle. Maybe not a good
> thing... 

I usually just decenter the mirror/tool, squirt on some CeO/water, and 
then spin the lap/mirror to distribute it.

> **** The pressure I'm applying is: "Working TOT, usually I just try to
> apply slightly more pressure to the trailing edge of the lap as compared
> to the leading edge of the lap.". Only enough to "grip" during MOT.

OK, just increasing the pressure should help the sphericity, but the 
pressure modulation I have described may be necessary to really get it 
spherical.

Remember, we don't care so much about sphericity, we want to get rid 
of the turned edge and the raised zone at the edge.  Then you can 
start figuring, provided it is polished out.

	Mike Lockwood

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