RE: [ATM] More Mirror Disasters!

["Thomas" <tomjan@ozemail.com.au>]

Flash heat the surface of your polishing lap so that the contaminant is
*in* the pitch and not on it. 

To do this wash of all the cerium oxide etc, and then with a heat gun or
small gas flame work the whole lap over real quick so just the top 1/16"
or so melts. This way the contaminant will be locked away in the pitch,
but you will have to re-press the lap to get good contact again...

On the other hand you could just ignor them scratches, remember the
spider vanes for your secondary support act like four huge
scratches.....

Clear skies,
Thomas Janstrom
http://www.tjanstrom.com
http://www.norsewines.com.au
"Your nobody until you've been ignored by your seventh cranio-facial
nerve."


-----Original Message-----
From: atm-bounces@atmlist.net [mailto:atm-bounces@atmlist.net] On Behalf
Of David Grennan
Sent: Wednesday, 8 June 2005 5:04 AM
To: atm@atmlist.net
Subject: [ATM] More Mirror Disasters!


Hi all,

Last evening while working at figuring my 8 inch f6.3 I managed to get
something between the lap and the mirror which resulted in lots of tiny
(almost imperceptable) scratches all over my mirror.  Even though I
tried scrupulously to clean up every single grain from previous
operations.  Hence my first question.  Would you guys tolerate these
tiny scratches and just move on, should I go back to fine grinding, or
is there a chance I can polish these scratches out.

Now my second question.  After a period of using the classic
parabolizing stroke.  I was able to observe my mirror moving toward a
parabola.  (I was continuing with this stroke when I got all the little
scratches).  After my second session of parabolizing I fully expected to
find my mirror closer to the required section.  I thought if I was close
enough I'd just forget about the scratches and get the job finished!
However to my amazement the foucault test shows me I'm back at a sphere
again!!  I have no idea how this occured.  I cold pressed for 1 hour
before my second session of parabolizing.  <aybe this wasnt enough.

So in summary my questions are.

1)  How (if at all) should I best deal with these fine sctratches.
2)  How could the classic parabolizing stroke bring my mirror back to a
sphere?

Confused :-0

Dave

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