Re: [ATM] Polishing question

[Mike Lockwood <melockwo@uiuc.edu>]

Anthony,

Anthony Anconetani wrote:
> I've completed fine grinding and poured the lap. I built the tool with
> Gugolz 64. I think there is a good amount of CEO embedded in the pitch.
> The channels are pretty clear at 1/4 inch. So this morning I did a cold
> press (to fulfill the required oath in Mike Lockwood's figuring notes)
> with an ambient temperature of ~80F for about 40 minutes (arguably a
> "warm" press I guess 8-). I also pressed with a some tulle for micro
> faceting. 
> I did some polish strokes and found the process to be what I would
> describe as "heavy". I would contrast this to the fine grinding with the
> tile tool and WAO. The fine grinding was very light and easy. I only
> needed light finger pressure. I did not need cleats to hold the mirror
> or tool in place. However, with the lap I needed to cleat the mirror and
> I needed a good hold on the top disk to move the disk. I did not feel
> slipping and grabbing. I would say the heaviness was uniform regardless
> of offset or rotation. Adding and removing water did not seem to change
> the feel.
> Does this "heaviness" to the process sound correct? Or is it possible
> the pitch is too soft?

Sounds good to me.  At the beginning of polishing the lap is not 
"broken in" and the pitch can grab quite strongly.  (However, the 
surface of the mirror still has millions of little pits and mountains 
on it, and that decreases friction.)

Watch the lap as you polish.  If the pitch channels nearly close after 
less than an hour of polishing, then the pitch is acting a bit soft 
and you might want to work somewhere cooler.  G64 at 80 degrees may be 
a bit soft, but it depends on how you melted it.

If the pitch does indeed appear uniformly imbedded with polishing 
compound, then just keep going.  If it doesn't, wet the lap a little, 
sprinkle on some cerium, and rub it onto the facets with a clean 
finger.  Then polish for a while.  You won't have to add polish for 
quite a while, and that will nicely charge the lap.  This is only 
necessary when you start using a new pitch lap.

After an hour your mirror should look shiny and reflect things at 
large angles (as opposed to reflecting at shallow angles after fine 
grinding).  At that point you are just getting started.

	Mike Lockwood


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