🚀 go-pugleaf

jcurtis@seqp4.sequoia.com (John Curtis) writes:

>I'm dragged my 8" mirror out last night (long in the making).
>Did about one hour of polishing using cerium oxide on a 
>opthalmic polishing lap (polishing pads stuck to the original tool
>per a S&T article.)

Interesting.  I was gonna try this in the not too distant future.  

>Things seem to be going well.  The only exception is a small 
>scratch (this long: --- ) which I am choosing to ignore.

*sigh* scratches are indeed annoying, but seldom fatal.

>Total polishing time is just under 4 hours, and the mirror looks
>reasonably bright, but not as bright as a wet mirror.


>When is enough?  Any hints?   I haven't used my Foucault apparatus on
>this guy yet.  I did look at the surface at 30x using a Rat Shack
>hand microscope and was shocked to see a pebbled surface.  This 
>may be underneath the actual top surface of the glass.  The lap 
>did start polishing the whole  surface immediately.

Interesting.  I would be very interested in knowing what the knife edge or
Ronchi patterns where like.  If you can see pebbling on the mirror, my 
guess is that something bad could be happening.  

>Please help me over my novice angst.

Well, if you wanna get over novice angst, you have to just keep
making mirrors until you become an expert :-) As a data point, I
just finished an 8" mirror which I spent about 8 hours of non-figuring
polishing time on (and just an hour or so to figure!).  Texereau
recommends about 15 hours for an 8" mirror, but most people at the
work shop seem to discount this number as overly cautious.  Some
mirrors also seem to polish out quicker than others (probably
because of better or worse lap contact).  The way I check mirrors is to 
aim a bright flashlight (I use a mini maglight) at the surface and see if 
any bright spots which don't move are visible at the edge.  The surface of 
the mirror should be barely visible, reflecting only a small amount of light.

If indeed these pads work as advertised, you may be able to get by with 
only 2-3 hours of polishing.  As I have not tried these yet, I can only 
parrot what was quoted in the Sky and Telescope article you referred to. 
When your mirror is done, please post (or email me) a short description of
how it all worked out.


			Mark (markv@pixar.com)