Re: [ATM] Not tde or tue, important oblate spheroid, ellipsoid

["lütfü" "çakmak" <lutfu_cakmak@yahoo.com>]

Hi Jerry,

I decided to try a my new idea which I have not seen
in literature, last time before returning to fine
grinding on my mirror which is "polishing chordal
stroke" at the last weekend. I think that because my
mirror need more curve on the center. 

Incredible ! ronchi lines was changed where placed
inside radius and outside radius opposite each other
at the end of only 30 min. polishing. Continued
increasingly reducing hangover part mirror from the
lap tool 1 hour too.

Firsly that caused getting ruined face as I guess.
Than I did it Narrow W as you described narrow W
stroke for 1 hour only MOT. Of course I did it which
your explaining about maintenance of lap. Here is
ronchi;

http://www.atmlist.net/contrib/lutfu_cakmak-at-yahoo-dot-com/lutfu_01_06_2008/

Well, is there a hole or a hill at the center of
mirror. I think that it is a hill. What should I do
for correcting.
 
And there is not tde or tue, isn't it?

Note:
Apologize again, my eng.language can not be properly.

Best regards,

Lutfu
 


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

> Well, it has gotten better than it was. Still oblate
> but much smoother.
> 
> First let me point you to where your lap needs
> trimming. Look at the channel
> running up and down in the center of the lap. At the
> top of that channel the
> first row of full size facets are pinching together.
> That is what closing
> channels look like, a pinch. You can see that the
> channel to the left of
> that one is pinching up there also. And now that you
> know what to look for
> you should see that there are a few more places
> doing the same.
> 
> You should also note that in this case those places
> that are pinching are
> near the edge of the lap. That could be because you
> are working MOT more
> than TOT or it could be that you have poured the lap
> on a flat tool and the
> pitch is thinner there and has to flow farther as
> the pitch is pressed
> thinner. It could be that the channels were not cut
> as deep there and less
> flow is required to fill the channel. There could be
> other reasons but you
> get the idea. The pitch flows and that is what the
> channels are for.
> 
> For what ever reason the channels are pinching there
> first. It is ok if you
> poured the lap on a flat disk. That is probably the
> main reason in this
> particular case. 
> 
> What you need to do to control the shape and texture
> of the mirror surface
> is to maintain the channels. You don?t have to trim
> the entire lap every
> time you trim. You could take a razor blade to those
> areas that are
> pinching. Don't make the channels deeper or wider in
> the center. Just trim
> where it is needed to make the channels fairly
> uniform in depth and width.
> It is quite likely it will continue to be the outer
> part of the lap that
> closes fastest so most of your trimming will be
> within 2 inches of the edge
> of the lap.
> 
> Notice that the facets are smaller squares in the
> center. The outer ones are
> spreading faster. It is impossible to have a grid of
> straight channels on a
> curved surface. But you want to make the outer
> facets closer to the same
> size as the center ones. The result of the work you
> have done you have
> inadvertently made a lap of graduated facets. In
> this case they are smaller
> at the center and progressively larger toward the
> edge. If you did this on
> purpose it would be to make the lap push the curve
> toward the oblate curve.
> No doubt that is some of the reason your mirror is
> oblate. Not the only
> reason.
> 
> On the other hand larger facets in the center and
> smaller toward the edge
> will push the curve toward the parabola and
> hyperbola. You do not need to do
> this method with this mirror.
> 
> Trim when needed but only where needed. Wash off as
> much of the pitch chips
> from trimming. It is pitch so it won't scratch the
> surface if you don't get
> it all off, but you do have to press it into the
> lap. The more chips you
> leave on top of the facets the longer it will take
> to press them in. Wash it
> well, paint it well with polishing slurry and press
> well.
> 
> Work only if the lap is pressed well and working
> smoothly. Stroke slow... as
> slow as you can go while maintaing smooth motion.
> 
> Jerry
> 
> -----Original Message-----
> From: lütfü çakmak [mailto:lutfu_cakmak@yahoo.com] 
> Sent: Thursday, January 03, 2008 9:36 AM
> To: Jerry; 'atm_list'
> Subject: RE: [ATM] Not tde or tue, important oblate
> spheroid, ellipsoid
> 
> Hi,
> Jerry, Thomas, Mitchell and all who replied my
> message. Thanks for your comment and suggestions.
> 
> Firstly I should explain that is before I have never
> used any strokes for figuring as W. While polishing
> only carried on 1/3 COC TOT and MOT equal times.
> But,
> my mirror gets curved lines in the course of time.
> 
> Jerry, I did it which your first suggestions as "
> Strokes about 2 1/2 to 3 inches long (3 inch
> maximum)
> in a W about 2 to 2 1/2 inch wide (1 to 1 1/4 inch
> each side of center)" along 1,5 hours with testing
> sometimes. At the same time, I have not know that my
> mirror being oblate spheroid. After working here is
> ronchi;
> 
>
http://www.atmlist.net/contrib/lutfu_cakmak-at-yahoo-dot-com/lutfu_12_29_200
> 7/
> 
> Than, I worked 1,5 hours too same strokes and here
> is
> ronchi;
> 
>
http://www.atmlist.net/contrib/lutfu_cakmak-at-yahoo-dot-com/lutfu_12_30_200
> 7/
> 
> Than, I have seen no change on face and I discovered
> oblate spheroid.
> 
> Than, I have polished my mirror 1/3 COC only MOT 3,5
> hours steady as Thomas suggestion. And I have seen
> still no change about ronchi lines. There are
> contrary
> to be normally inside or outside radius. Here is
> ronchi;
> 
>
http://www.atmlist.net/contrib/lutfu_cakmak-at-yahoo-dot-com/lutfu_01_01_200
> 8/
> 
> Maybe, the best way is returning to fine grinding
> (800
> grid). Getting a good sphere than polising again so
> get rid of TDE etc.
> 
> Happy new years
> 
> Lutfu
> 
> 
> 
> 
> 
> 
> --- Jerry <wa4guu@verizon.net> wrote:
> 
> > Hello Lutfu... happy new year.
> > 
> > We seem to have hijacked your thread. I'll bring
> it
> > back to you now by
> > answering your question.
> > 
> > You are right, it is oblate.
> > 
> > I'm sure some of us did see your oblate shape. The
> 1
> > inch wide turned up
> > zone near the edge is part of the oblate.  From
> > there into the center is
> > quite rough and is more important defect than the
> > oblate shape.
> > 
> > The oblate shape is not a big problem. It is
> easily
> > fixed. It takes minor
> > adjustments of your stroke to make it go away.
> What
> > I suggested you do
> > should make the central area smoother and also
> take
> > the curve closer to a
> > sphere.
> > 
> > Don't let the lap's channels close up. They don't
> > have to be so deep and
> > wide, maybe 1/4 inch deep and wide is a good size
> to
> > start with. You might
> > have to trim frequently to keep them about that
> > size, but it is good that
> > the lap will work very predictably. If you make
> the
> > channels deep and wide
> > and then trim when they close up there is much
> > variation of the lap action
> > from the fresh trimmed wide channel and the about
> to
> 
=== message truncated ===



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