заготовки из кинескопов

[technolog]

Мне кажется, что из экранов кинескопов
старинных цветных телевизоров можно
выкраивать вполне приличные заготовки для
астрономических зеркал.

[Unforgiven]

На эту тему была интересная беседа на atm-digest@shore.net <atm-digest@shore.net> - почтовом форуме тема:ATM Cheap mirror blank ideas. Вот пара сообщений на эту тему:

A possibility that I explored was to use the front of a video picture tube.
THIS IS VERY DANGEROUS AND GREAT CARE NEEDS TO BE TAKEN.BOTH BECAUSE OF THE RESIDUAL CHARGE ON THE TUBE AND THE VACUME DRAWN ON THE TUBE. BEWARE!

I have found the glass on the front to be .5" to .75" thick depending on
the tube.

Make sure the power is unplugged.
Open the case, you can be brutal here as it isn't going back together. Unplug the plug from the back of the picture tube. You can wear rubber gloves to do this, but that end should be pretty cool, (electronically speaking).
Wrap an old towel arond the pins that are protruding from the neck and cautiously
tap on the end of the tube till you hear the vacume escape. If you wail on that
glass the whole thing will shatter and hurt you. The glass is thin at the pins and
very easy to crack. You can also wiggle the pins and sometimes break the seal and
release the vacume. Once the vacume is gone pull the high voltage wire out of
the side of the picture tube. DON'T TOUCH THIS WIRE TILL THE VACUME IS GONE!!

Once the vacume is gone, remove the tube from the chassis and throw the
rest away. Now you must cut the back from the front of the tube. If you look at
the tube you will see a seam of ceramic material towards the front, where the tube
is welded together. I go just to the front of that and etch a line around the tube
and use a hot wire or pencil torch to crack the front off of the tube.

Now you have a chunk of glass with sharp edges and a precast curve in it. Cut and
grind for shape then grind and figure for finish.
I was originally fascinated by the high voltage. I cut my first tubes for an art
project involving bells but never thought about the mirror possibilities until a nephew who was building scopes at 12 realized the solar collectors I was making from the fronts had accurate curves. He took one and achieved and F3.5 14" mirror, though he told me the curved had to be flattened and
he sweated the figuring because the glass got very thin.
I currently have the front from a 14" MAG SVGA monitor in the garage. I believe I could get a clean 9" circle out of this. The existing sagita is about 5/16th of an inch. Using the short form equation from Howard's book this runs out to about a 32" ROC or a 16" fl. Not quite an F2. The glass is just a tad over 3/8ths of an inch thick. For an F4 at 9 inches I would need a 72" ROC which yields about 5/32nds of an inch of sagita. Which means I am going to grand away about half the glass to flatten and figure the curve and it will be very thin at the edge. It should also be a rather nifty meniscus lens.
As a side note, the glass being rectangular looks more like a toroid than a spherical curve.

Вот такие дела.

[Anonymous]

Может я заблуждаюсь,но у меня есть опасения что когда стекло было кинескопом и находилось под действием атмосферного давления (долгие годы)оно могло потечь и после разгрузки оно останется с внутренними напряжениями.И возможно через годик другой форма зеркала исказится.
Александр.

[Unforgiven]

А из какого стекла изготовлен кинескоп? Это случаянно не флинт? А то в обсуждении эта мысль пробежала.

[technolog]

Кинескоп проектируется так, чтобы всякое
коробление и деформация экрана были исклю-
чены. Механические свойства, однородность,
качество отжига стекла кинескопов -
превосходны. По составу это стекло весьма специфично - в нем много бария и свинца,
оно не может быть соотнесено ни с каким
оптическим стеклом. Коэффициет расширения
его весьма велик- иначе его нельзя спаивать с металлом, химическая же стойкость остав-
ляет желать лучшего. Но зато бесплатно!
Поразительно, сколько церемоний нужно
иностранцам, чтобы разбить обычный кинескоп!