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Re: [ATM] Not tde or tue, important oblate spheroid, ellipsoid
Hi Jerry,
I worked on my mirror yesterday as you described.
1- 15 minutes short stroke Center Over Center
(half TOT, half MOT)
2- 15 minutes 1/4 - 1/3 diameter narrow W stroke.MOT
3- 15 minutes short stroke Center Over Center
(half TOT, half MOT)
4- 15 minutes 1/4 - 1/3 diameter narrow W stroke.MOT
Of course tested while these combination of stroke. I
did not see starting to go back toward oblate and
going far from the sphere. But, it didn't improved in
my opinion. Tde is still remain on the edge maybe less
this time. And I have seen still there is a small
hole. Notwithstanding last time I did "The W Edge
Deepening Stroke" for 5 minutes, only to see what's
changing but it didn't change something.
I did not want to do something other than those
because I know, this phase of making mirror is very
important and I have to be careful.
Here is the last ronchi;
http://www.atmlist.net/contrib/lutfu_cakmak-at-yahoo-dot-com/lutfu%201_13_2008/
Best regards,
Lutfu
--- Jerry <wa4guu@verizon.net> wrote:
> Hello Lutfu
>
> The lap looks much better now. There is some turn
> down on the edge. The
> shape is very much improved. I see your second
> comment about the hole. It is
> a small hole, so shallow that is does not matter.
> The shape is for all
> practical purposes a sphere with a little turned
> down edge. Much better than
> before.
>
> Now you have to work in short sessions. Do not work
> more than 10 or 15
> minutes in one session. You have to test between
> sessions. You can do more
> work in 10 or 15 minutes than is necessary to
> parabolize. Even if you are
> doing something that will take longer to accomplish,
> you should not work
> longer. If everything goes right it will take
> several sessions to finish. It
> may take many more. Sometimes 5 minutes or less
> might be enough.
>
> Let's see if you can make the edge better without
> going far from the sphere.
>
>
> Use the short stroke Center Over Center for 15
> minutes. The stroke length
> can be anywhere from 1/4 D to 1/3 D Don't do this so
> long that it goes back
> to an oblate curve with ugly zones. Only do it for
> 15 minutes. Look at it
> with the Ronchi test. The edge might get better. It
> will start to go back
> toward oblate. But you won't do it long enough to go
> far. Don't do long
> sessions of the short COC strokes. Even if the edge
> improves and it hasn't
> gotten oblate or developed zones, you will not do
> the same thing next
> session. The next time will be something else.
>
> You want to keep the curve as close to a sphere as
> possible while you
> improve the edge.
>
> Do the short COC stroke for 15 minutes, no more. You
> can do either MOT or
> TOT, and if you wish you can do half of the time MOT
> and half TOT. Test to
> see the results. If the edge is good go on to
> parabolizing. If the edge is
> not yet good do 1/3 diameter narrow W stroke for one
> session. Make the width
> of the W about 1/4 or 1/3 D. Test again. If the edge
> still needs more work
> you can do another session of short COC strokes.
>
> If the combination of the short COC stroke and the
> narrow W results in the
> mirror going oblate then make the W a little wider.
> If it goes toward the
> parabola, narrow the W. Adjust the stroke so the
> combination of short COC
> and the narrow W holds the mirror close to a sphere
> while the edge gets
> better.
>
> When you get the edge satisfactory start
> parabolizing. Now that the lap is
> in better shape and the mirror does not have a hill,
> the best stroke to
> start parabolizing with is the one for edge zone
> correction.
> "The W Edge Deepening Stroke"
>
>
http://stellafane.org/atm/atm_mirror_ref/atm_strokes.htm#The%20Normal%20Stro
> ke
>
> I like Mike's illustration better.
>
>
http://bi-staff.beckman.uiuc.edu/~melockwo/mirror_making/full_lap/full_lap.h
> tml
>
>
> the one labeled "Modified stroke for more edge
> correction at start of
> parabolizing".
>
> Only do that for a short period before testing. Do 5
> minutes of that and
> test. You don't have far to go from a sphere to a
> parabola and that could be
> enough. You will want to see how far 5 mninutes
> takes you before doing more.
> You will also want to see how well the correction is
> going on from center to
> edge so that you can adjust the stroke in the next
> work session... if there
> is a next session.
>
> It is not likely that you will make your edge
> perfect, so you will have to
> decide when it is good enough.
>
> You do not have to bend the Ronchi bands much from
> the straight bands of a
> sphere to be fully parabolized.
>
> Keep the lap in good condition.
> Slow strokes. As slow as you can go keeping the
> stroke smooth.
> Don't work too long. 15 minutes is a long session.
> Some might be only a few
> minutes. Many short sessions will do much better
> than many long sessions.
>
> SLOW STROKES.
>
> Jerry
>
>
> -----Original Message-----
> From: lütfü çakmak [mailto:lutfu_cakmak@yahoo.com]
> Sent: Saturday, January 12, 2008 5:03 PM
> To: Jerry; atm_list
> Subject: RE: [ATM] Not tde or tue, important oblate
> spheroid, ellipsoid
>
> Hi Jerry,
>
> I agree with you. Already I have worked for about 5
> months on this mirror. One time I had to returned to
> fine grinding. It is a training mirror for me.
> Actually I will make a 10" for planets and a 15" for
> deep sky. 15" blank is ready for grinding and I have
> waited 10" pyrex blank from a my frend will to send
> from USA.
>
> After 30 + 15 min. the big W stroke + 15 min. the
> big
> W stroke using rouge here is ronchi;
>
>
http://www.atmlist.net/contrib/lutfu_cakmak-at-yahoo-dot-com/lutfu_1_12_2008
> /
>
> I think my mirror returned to shpere, but a litte
> bit
> a hill still remain and there is a little bit TDE on
> the edge, for my part.
>
> Well, afterwards what is your suggestions.
>
> Unfortunately I have not yet a foucault test device.
> Surely I will have to make one.
>
> Best regards,
>
> Lutfu
>
>
>
>
>
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