Re: [ATM] slow polishiing

[Guy Brandenburg <gfbrandenburg@yahoo.com>]

Bill,

After 7 hours of work with cerium oxide, you are
probably polished out, unless the fact that you were
pressing WITH the netting in between the mirror and
the lap messed things up. That you don't want to do in
the future. 

Warm up the lap in some hot water (hot like out of the
hot-water tap, not boiling hot, i.e. something like
130 to 140 degrees or so) until the lap is fairly easy
to press a fingernail into, then take it out of the
hot water, lay the netting over it, then press down on
the mirror down onto the lap until the netting makes
little dents all over the lap. Then take the netting
out, apply some polishing compound, then press for
20-30 minutes or so, with some weight. Don't make
everything so hot that the channels close up when you
press the netting into the lap or the mirror onto the
lap. Having the mirror relatively cool will help to
cool down the lap in a hurry. 

Then try different polishing regimes. See other
comments below.

Guy
--- Bill Mitchell <astronutski@yahoo.com> wrote:

> Actually, with the two radically different ROC's I
> really don't know
> how to tell where the 'real' ROC is.  Do you always
> go off the
> center? 

For yoru purposes, right now, the point at which all
of the lines and gaps pretty much disappear into a
single blob, you can consider to be approximately the
center of curvature. Later on, when you get closer to
a single sphere all over, then you can measure the ROC
more carefully. I just wanted to know, mostly, whether
you were inside or outside the COC, and you still
haven't told us, and the # of lines per inch on your
grating, which ditto.

> I just didn't think I was even close to being
> polished out yet so I
> didn't bother noting the location.  I was under the
> assumption that
> the inner sphere would grow as polishing progressed,
> and that wasn't happening.

That is obviously not the case. Don't believe
everything everybody tells you, especially if it goes
against the evidence you can see for yourself. Along
with Bob, I would estimate that after about 7 hours of
polishing with CeO, you are probably mostly done with
plain polishing, especially based on the looks of both
of the images. 

To make things really smooth, try switching over to
rouge. It's messy, but it makes for a much finer
surface, and it goes slower, so you are less likely to
overshoot a perfect surface.

> I know I have to test more with the laser and sun
> test to determine
> if it is polished or not.  I know I can still see
> the laser enter,
> although it is pretty dim.  Maybe I jumped the gun
> and shot those w/o
> being polished.  My original question was meant as
> 'am I polished out
> yet' and 'do these images help evaluate that'?  

Another way to check for polish is to get a
non-frosted light bulb (not high wattage) and look at
the reflection of the filament in the mirror, against
a black background under the mirror and in back of the
bulb. If it's really polished out, then you won't see
grayness right next to the filament. 

> Not so much as what
> corrective actions to take based on the images
> (assuming it is polished out).
> Sorry if I caused any confusion, as I have more than
> enough to go around 8^).
> 
> -Bill
> 

=====
Guy  Brandenburg
Washington, DC
My home page:
http://home.earthlink.net/~gfbranden/GFB_Home_Page.html
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