Re: ATM 14" is still spherical... and a little rough.

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

I have found that to soften the surface of a hard lap just give it a quick
wipe with turps, leave it face up till it is no longer sticky then press for
good contact.

Clear skies, Thomas
http://www.geocities.com/t_janstrom/
----- Original Message -----
From: Sam Orawski <samorawski@3web.net>
To: Day, Jack <jday@clinitech.net>
Cc: ATM <atm@shore.net>
Sent: Tuesday, March 27, 2001 9:30 PM
Subject: Re: ATM 14" is still spherical... and a little rough.


>
>
> Jack
> Sounds like your lap is very hard, which will tend to pull the figure
uphill
> towards a sphere and then later, possibly an oblate spheroid.
> You may need to use longer strokes, or more likely a softer pitch lap. I
> have in past, poured softer pitch right over the existing hard lap to
> parabolize.
> Have patience to press for good contact, slow down your parabolizing
stroke
> speed and let the mirror reach equilibrium after retouching. This will
> usually keeps you out of any major problems.
> Clear Skies
> Sam Orawski
> Hamilton Ont.
>
> ----- Original Message -----
> From: "Day, Jack" <jday@clinitech.net>
> To: <atm@shore.net>
> Sent: Monday, March 26, 2001 1:57 PM
> Subject: ATM 14" is still spherical... and a little rough.
>
>
> >
> > Hi All,
> >
> > Last night I re-channeled and pressed my lap.  Then threw the nylon
> netting
> > on and pressed again.  The lap seems to be cutting better, but the short
> on
> > the edge, long in the middle strokes => wWw are having no noticable
> affect.
> > (At least the ronchi lines are still sraight!)  This is after about an
> hour
> > of trips around the barrel,  but with just the pressure of the lap.  The
> lap
> > is 2 3/4" thick and weighs quite a bit.  The mirror has been setting
over
> > night in the test stand and I hope that any distortion caused by putting
> it
> > on the stand should be absent by now!  So I will test it when I go home
> for
> > lunch. Perhaps the center is deeper than I think but was distorted by
the
> > heat of my hand while washing and seting up in the test stand.  Also
would
> > there be any merit in making a six inch or so sub-diameter lap to take
to
> > the class this weekend?  Also thanks to all who have helped so far.
> >
> > Jack
> >
>
>
>