Re: ATM 'Frozen' liquid mirrors

[PFAFF2@delphi.com (Robert C. Pfaff)]

>Hello Peter,
>It may be, that the rotor in your motor is unbalenced.  Balenced electrical
>motors are an unnecessary expense, in potters wheels.  If you balence it,
>retrofit with silicon nitride bearings, true and align the pulleys, you
>should be better off.  Otherwise, I need a potters wheel  <smile>
>
>-Andy
>
>
><snip>
>
>I rewired the speed controller in
>>the foot paddle and replaced the variable resistor with a fixed
>>one to keep the speed constant.  Still had problems
>>with vibrations despite putting everything in a sandbox as my
>>laser holography friends suggested.  I am not sure whether the
>>problem is due to inadequate damping from the ground or a worn
>>bearing in the motor drive. Probably both. 
>
><snip>
>

As this seems to be a thread that will not die I have some questions.
People on this thread seem to think that if a vibration free table
can be made then a precison optical surface can be had.

The people making those large spin cast mirror have ripples on the glass
not because of bearing vibration but because the surface of the glass
cools uneven and surface tension. Now it would seem to me if epoxy
is free from these problems a person could  just pour some epoxy
in a dish and have a nice optical flat. Mercury makes great flats.
Now you could can use a congrete substrate if you wish. If this worked then
I would think that there is some merit in doing this project. 

This is not a flame but just how an old dog looks at things.

Bob Pfaff