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Re: [ATM] Not tde or tue, important oblate spheroid, ellipsoid
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
> be trimmed closed
> channels. If 1/4 inch doesn't work well you can make
> it wider next time.
>
> Press well before working and stroke slow. Strokes
> about 2 3/4 inches long
> in a W about 2 1/4 inch wide, give or take a little.
> You can do this either
> TOT or MOT.
>
> Slow.... Slow strokes. As slow as you can go and
> keep the motion steady.
> Work for about 1 hour and take another picture or
> two.
>
> Or you can try one of the strokes others suggest.
>
> I like the inside ROC Ronchi. About 5 lines showing
> on the mirror tells me
> just about all I need to know in most cases. Some
> other people like some
> other way.
>
> Jerry
>
>
>
>
> -----Original Message-----
> From: lütfü çakmak
>
> Hi all,
>
> Interesting, nobody could see who replied to my
> first
> message, about problem on my mirror and warned me. I
> was concentrate on tde or tue like every atm. But,
> couldn't see the big error on my mirror. Because the
> ronchi lines are contrary to be normally inside or
> outside radius ;
>
>
http://www.atmlist.net/contrib/lutfu_cakmak-at-yahoo-dot-com/lutfu/
>
> (images named ri=inside radius, ro=outside radius)
>
> Well, when I put +1.5 value of conic on RonchiZ prg.
> I
> see same lines on my mirror. I think that, this is a
> oblate spheroid or ellipsoid, isn't it? What can I
> do
> for correcting?
>
> Another interesting thing, nobody discovered who
> living a few atm in my country too. :-)
>
> Apologize, my english language can not be properly.
>
> Happy new year,
>
> Lutfu
>
>
>
>
>
>
>
>
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