Re: [ATM] Figuring Methods

[Kevin MIchael Zabbo <chaosopher23@yahoo.com>]

I'm watching the figuring postings and I can figure
(no pun intended) that the best way to start figuring
is to start from a sphere and turn the edge down
evenly from where the Raleigh criterion for that f/D
mirror starts, and turn it down carefully.

Just my distillation, mostly because I have a
hyperboloid of about 1.7 or so indicating that I have
a really huge TDE and I have to dig a hole in the
center that's a little more than a micron deep.  So
much for giving my arms a break!

Kevin of (rainy) Eastern Iowa
Seeker of the Darkness

--- Jerry <wa4guu@verizon.net> wrote:

> Hello again Mike. I'm still practicing.
> 
> I have changed subject title...to better fit the
> discussion since it is
> settled and agreed that I don't know much about
> edges.
> 
> I enjoy the discussion. This is why I usually answer
> requests for figuring
> advice.  I know there are different methods. I just
> don't know what they
> are, so I want to hear from you and others. Mike,
> you are one of the few who
> will step up with advice, and of a more thorough
> nature than most others
> will.  I thank you for that. Just because I 
> 
> The ones asking advice should not take every
> disagreement on figuring
> technique to mean one is right and the other is
> wrong. I may well try some
> of the things I have argued against the next time I
> make a mirror. There are
> different methods and some might be faster and some
> slower. Sometimes slower
> might be better and sometimes faster is nice.  Some
> methods may not be as
> predictable as others. The reader has the option of
> taking or discarding
> advice. I think in most cases they do not take much
> of it anyway. They might
> remember it when faced with some particular figuring
> challenge they can't
> find their own solution to.
> 
> So one maker may find some methods more sutiable to
> his style and another
> maker finds others more favorable. And some have
> only learned one way.  I am
> one of those because I learned in isolation from
> other mirror makers. If it
> isn't in Texereau's book, or I didn't make it up
> myself, I probably don't
> know it.
> 
>  
> I am speaking of TOT.  There are MOT analogies to
> the TOT. The operating
> factor is the pressure of the lap on the glass. If
> you can duplicate that
> MOT as it would be with the TOT, the results will be
> the same.
> 
> I will answer your concerns..
> 
> -----Original Messages
> From: Mike Lockwood 
> And From: Jerry
> Subject was:  Re: [ATM] TDE (That Darned Edge)
> Subject now" Figuring Methods
> 
> ********************************
> 
> Jerry wrote:
> > If you were experienced at using accented pressure
> and using the
> > right pressure, I would suggest starting with very
> little pressure
> > just a little inside the edge, and as you stroke a
> W inward to the
> > 30% you increase pressure steadily as you go
> reaching max at 30%
> > and then reverse back outward while reducing
> pressure.
> 
> Mike wrote:
> 
> I would like to clarify that a little more.
> 
> If I were to work the lap inward (I think you were
> talking about TOT
> work) using that "pressure profile" (increasing the
> pressure while
> moving inward), I suspect I would find that it very
> effectively dug a
> hole near the center.  Using accented pressure near
> the center of the
> mirror will change the shape much more quickly than
> near the edge, and
> it must be done carefully, with knowledge of what
> can go wrong.
> 
> 
> Jerry's answer
> 
> If you stop the inward travel at the rim of the
> crater this should not
> happen. Keep in min the rim of the crater is not the
> end of the high glass.
> Just as the edge you want minimum and increasing
> wear to the rim, from the
> rim inward you still want some removed but
> decreasing to near nothing in the
> center.  In this case the 30% is closer to the
> center than the edge but
> there is still some there.  If you do this until the
> crater is gone you will
> actually have a flat center to the 30 percent zone.
> Until one is well
> practiced at this. One time around is enough at any
> one work session. In the
> case of Robert's mirror the defect should be history
> after one session. That
> is why I stress the short sessions.  There is no
> reason to take hours to
> remove a hole in the center.
> 
> 
> *******************
> 
> Jerry wrote:
> > A bit easier is to use the same pressure for the
> entire W. and some
> > method of increasing wear in the inner zones such
> as working the W
> > from the edge inward but when you reverse to go
> back outward only
> > go 1/3 or 1/2 way from the 30% to the where you
> started at the
> > outside of the W.  That will give more work near
> the rim of the
> > hole.
> 
> Mike wrote:
> Again, one must be careful because the center can
> deepen very quickly.
> 
> Jerry's answer 
> 
> The difference is that I am going for a different
> curve than you are. I am
> going for a parabola of a slightly shorter focus.
> There is less glass to
> remove. By adjusting the target curve to the one
> that touches the very
> center and the very edge.
> 
> ***************
> 
> Jerry wrote:
> > The variable pressure is the superior method
> 
> I must disagree - there are few absolutes in mirror
> making, and I 
> think this depends on the pitch hardness and the
> operator.  With soft 
> pitch, using lots of pressure will make it flow
> quickly, and the 
> "active area" of the lap will move inward rapidly. 
> I have seen this 
> cause deepening of the center when de-correction of
> outer zones was 
> the intended effect.
> 
> I semi-agree. Any method well done is as superior.
> Variable pressure is more
> easily done to a superior result. There are patterns
> of interlacing from one
> step around to the next going a different distance
> inward that is
> particularly useful in the center, where if you went
> that far inward on
> every position around the mirror you would dig a
> hole or dimple.
> 
> The deepening you are speaking of is because by
> keeping the pressure too far
> out you have altered the radius out side the central
> area to a longer radius
> making the center comparatively deeper even with no
> wear in the center.
> 
> Lots of pressure is relative.  If I remember
> correctly about 5 pounds is the
> max pressure I use on a 12.5 inch. I know the feel
> and I pressed a scale one
> time to see but just don't remember for sure. I
> think 3 pounds or so would
> be adequate for an 8 inch. One will learn that
> rather fast if they look at
> the surface frequently and see how fast it moves
> glass
> 
> The active area is the lap and the inactive area is
> where the lap isn't.
> With the pressure on the side of the lap inside the
> edge, a difference of
> radius if formed between what is worked and what is
> not. That boundary is at
> the edge of the lap. That is why we think of the
> edge as being where the
> 
=== message truncated ===


I published my first novel!  You can get it here, from the publisher!  
http://www.publishamerica.com/greetingcardpro/pickup.asp?CardSentID=126045&rID=48283



Their search stringbox is on the right side about halfway down.

search using my name:  kevin michael zabbo
and it will take you right to my book page.

The title is anna's blood, which also takes you there.

Please order your copy soon!  I love you!

__________________________________________________
Do You Yahoo!?
Tired of spam?  Yahoo! Mail has the best spam protection around 
http://mail.yahoo.com 
_______________________________________________
ATM mailing list http://www.atmlist.net/