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

["Sam Orawski" <samorawski@3web.net>]

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
>