Re: ATM Astigmatism on 20 inch thin mirror

["Martti Koskimo" <martti.koskimo@kolumbus.fi>]

<Finally I made the bearing joints  from  cone shaped polished steel( like
<bullet) tenons  and this is put inside  cone (bigger angle) shaped Teflon.
<There is no problem in fixing the Teflon. Using screw threaded Teflon bar
it
<is trivial to  screw it to any material ( even in Teflon)
<This is like a dream bearing. So good that I converted all my mirror
<flotation systems to the same.

I was asked if I made the bullet cones myself

Yes,  the' bullets' are self made. It was not difficult at all. The raw
material
was M8 stainless steel screw rod.
25 mm long ( and longer) bits was sawed.  Then it was inserted to small
lathe. A Lathe is
not indispensable. Electric drill will do the same.
You must only have a ' holder ' for the drill. Then you take a file and file
the bullet shape
while  the rod is revolving in the drill. sounds complicated but it is very
easy and takes no time at all.
After there is bullet shape use a set of abrasive cloth and you get nice
polish on the bullet tip. This certainly  while the bit is revolving in the
drill.
And there is the other 'screw' side of the rod for easy fastening.

The Teflon side is still easier.  Just find a suitable sinking cone drill.

And yes,the triangles are not attached. No need for that. There are supposed
to be always lateral stops (sling etc.) and safety stops to prevent mirror
from falling.

This was the only support system and the only way I was able to eliminate
astigmatism from my 700mm Dia 30 mm thick ' bad glass' Pyrex mirror.
Probably I just blamed too much the glass while the main blame should have
been improper
support and improper handling of the mirror.

The worst astigmatism I have ever seen was when the mirror was policed on
the Dental Stone table covered with pitch squares ( 10 waves or something )


Martti Koskimo