Re: [ATM] Persistent turned-up-edge in mirror

["Jerry" <wa4guu@verizon.net>]

.......

Well anyway... That is why I made no suggestion about methods for fixing
TUE. (I cut out all of my reasons why for brevity and besides, who cares why
anyway?) Almost anything will fix it. Just about the only thing that won't
fix it is short centered strokes. That is how you make it. It is proven that
in the hands of most all, short center over center strokes makes an oblate
with a TDE. I suspect (emphasis on that word suspect) there is a TDE on the
outside of that turned up outer zone. But until it is fully polished, what
does it matter? Not much.

How would I fix it?  In this case for sure, I would just quit making it.

If my normal polishing stroke produced with certainty something deviating
from a sphere more than just slightly oblate (or slightly prolate) I would
consider the stroke to be "wrong". I would adjust the stroke length and side
until I found a combination that produced something reasonably spherical. A
TDE almost always comes with that oblate. But on a first mirror no big deal.

Once I learned what makes a reasonably spherical surface, that would be my
standard polishing stroke and I wouldn't spend much time looking at the
shape until polishing is complete.

I cut some stuff out here too.

I read that chapter in ATM Jim pointed to. Read it before, more than once.
There are some things in those books (ATM 1, 2, 3 and Texereau and others
too) that I disagree with. I think some things are just plain wrong. Don't
think it could be me. I think every technique that I use and everything I
believe to be true about mirror making is in them too. There is nothing new
under the Sun.

These books are always a good read when pulling one off the shelf. Reading
those books would provide many ideas about TUE and all those other things.
Experience with those ideas is attained the old fashioned way, through
experience.

As for using the fingers for figuring, (I've done it and I cut some more
drivel out here). Whether I would suggest someone try it or not, or what I
think the results might be was in what I cut out. If you don't have the
experience you only have hearsay.

Jerry


Jim Burrows wrote:
> Hey, whole-mirror strokes aren't the way to attack TUE!  Go around the 
> edge with a small tool (or your thumb).  "Three revolutions of the 
> mirror is enough of this without testing to be sure the action is 
> where it is wanted and not producing a ditch."  A.T.M. 2, p. 43, 1946.


Mike Lockwood wrote:

I must (respectfully) disagree with that 60-year-old advice.

First, relating to the previous question on the list, if someone has 
to ask how to fix a TUE, they are not ready to use their finger as a 
polishing tool

_______________________________________________
ATM mailing list http://www.atmlist.net/