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Vacuum Deposition/Mirror Aluminizing

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Q. Hi,

I am interested in making mirrors for telescopes and need to get info on the net about making a small home vacuum deposition system. It only needs to be small, to handle mirrors up to 10 inches in diameter. I have a 'fair' idea how the technology works, but have found no web pages out there that have a 'how to make' feel to them. Surely there is someone out there that has made a small unit of their own and posted it on the net, I just can't find it. Every search that I have done, returns companies that sell expensive equipment or specialize in coating, this is of no use to me.

Please, if you know of any sites or pages out there that have info on the construction of a vacuum deposition/bell jar aluminizing system, post the answer here.

Thanks for all the help,

Simon Williams
- Australia

How to Make a Telescope


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A. There are companies that sell laboratory sputtering equipment around $5000 to 10,000. This is, I think, lowest possible investment you need, and I wonder if it is worth your need. The Society of Vacuum Coaters [Albuquerque, NM] maintains a vendor list.

Mandar Sunthankar
- Fort Collins, Colorado

+++

Q. Hi Simon,

Did you find some information on aluminizing telescope mirrors?

Matthew Lovell
- Ohalloran Hill, sa Australia


+++

A. Simon.

I do vacuum coating as my job at Liverpool University and from time to time have to repair and/or cobble something together just to keep costs down. Anything and everything connected with vacuum technology is extremely expensive. We recently had to replace a 12 inch bell jar.the cost was about £400 sterling. A simple penning gauge head and meter costs about £200. I could go on! To build a vacuum system from scratch to produce a vacuum of approx. 5x10-5 microns (or torr) which is the ballpark target vacuum. Constructing a DIY vacuum system needs full machine shop facilities including machining(metal), welding (argon arc), silver soldering, and a sound knowledge of vacuum technology. Then comes the cost of the vacuum pumps (you can't make these things yourself). Typically a rotary pump (vacuum 10^-3 torr)for a 12 inch bell jar will set you back £1500. A diffusion pump (10^-2 to 10^-6) would be about the same price. On top of this you would still need to buy rotary pump oil, diffusion pump fluid (silicon or polyphenylether) and a pirani and penning gauge together with the reading heads, not to mention the valves -- at least 2 and a water-cooled baffle valve. I hope I am not depressing you and I wouldn't want to put obstacles in your way. I wish you good luck with your project. If you need any help or advice I will gladly help.

P.S. I re aluminize my own 8-inch mirror on a regular basis.

Regards,

John Naylor
- Merseyside, United Kingdom

A User's Guide to Vacuum Technology


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A. There is a Yahoo! list devoted to those who perform vacuum aluminization of optics, at the hobby level. As for myself I have evaporated copper and silver, but have not yet achieved levels which permit the use of aluminum. The group url is: http://groups.yahoo.com/group/vacuumx/

Bill Arcstarter
- Cincinnati, Ohio


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A. Like you I an interested in trying to cobble a homebrew mirror coating setup for astronomical mirrors 10" and under. The most useful info I have found is from the Saint Petersburg Astronomy Club website. Hope this is what you've been looking for?

Rick Gyesky
- Fair Lawn, New Jersey


+++++

A. I too am cobbling together a home vacuum set for coatings. Amateur Telescope Making Vol. III describes a home sputtering setup and further suggests that such perfect vacuums may not be required for adequate optical thin film deposition. Admittedly this text is dated, but if you could coat glass in 1954 at 2-3 torr, you can probably coat glass in 2005 at 2-3 torr.

Also, take heart. I just purchased a Welch Duo Seal 2 stage pump for under $200 dollars. Specs say it's capable of 0.0004 torr, but that's under ideal conditions. I'm compiling plate glass to build the actual chamber. Hoping to adequately seal with Silicone caulk strategically applied in a fashion that as vacuum increases the seals become more compressed in the joints thus improving the seal as vacuum grows. I don't think we really have to spend a fortune to do this. I'll try to post again as I have successes and failures to report.

Kenneth Staton
Tampa, Florida


+++++

A. This is in response to the gentleman in Tampa/St. Pete. Silicone sealant will not seal to a high vacuum trust me. Just a helpful reply.

Glen Thiess
- Clearwater, Florida


++++++

A. Also check out the bell jar. I think that the address is belljar.net. It is devoted entirely to amateur vacuum.

James Makela
- St. Louis, Missouri


++++++

A. I'm wanting to resilver or aluminize a mirror from a microfiche viewer. The ultimate purpose is to replace a broken final mirror in a Proxima digital video projector.

Ultimate perfection is NOT essential. It just has to be shiny and tough enough to withstand occasional wiping with a soft cotton cloth.

The mirror is on a panel that flips up so it's exposed to being touched. Mirror touchers get nasty looks and lectures about not touching! I'd love to know who BROKE the mirror.

A replacement isn't available, which is why I'm cutting this mirror down. It was free for cost of shipping but it's filthy and has some little bare spots and the coating is very thin. (A swipe with Eagle One Nevr-Dullamazoninfo wadding polish took the coating off.)

And now for another remark. I've found several versions of the silvering process that takes several nasty chemicals.

There may be an easier way. Some years ago on an episode of "The Furniture Guys", they went to a shop that re=silvers mirrors. The process shown was:

1. Strip the mirror.

2. Clean the glass.

3. Pour a tin chloride solution over the glass.

4. Tip off the tin chloride and pour silver nitrate solution over the glass. (I think that was it, definitely silver something. ;-)

The result was a practically instant coating of silver. I was amazed at the simplicity as it was done in realtime from the cleaning on.

Gregg Eshelman
- Weiser, Idaho


February 28, 2009

A. I just bought a 25 cm dia X 50 cm l vacuum pressure vessel for US$45 and I looking to build a sputter coating system also. I have a vacuum pump and a gauge Ebay is amazing. Even if it doesn't work out I'm going to freeze dry fruit gels Try and find a huge vacuum chamber as possible once you have successes you will want to build bigger mirrors. Then next build a blank mirror oven.
Don't be put off by the naysayers just keep an eye out and read up on how its done and be creative. Lots of amateurs have gone on from hobby efforts to professional industry just by daring to try. You can do anything you want.

Its a compass not magic

Allan Jensen
- Bega NSW Australia


December 11, 2009

A. In addition to the vacuum system... all sealants,oils and rubber tubing as well as other materials directly in contact with the vacuum must have a low vapor pressure so as not to contaminate the vacuum. Then you must have a transformer and a tungsten filament to melt the aluminum sample in the vacuum chamber. The aluminum vapor then will deposit on the mirror if the vacuum is low and not contaminated. The cost will be considerable and it is my recommendation to have it done commercially and to have the coating well done and the proper thickness.

Max Gersenson
- Sequim, Washington



October 24, 2012

Q. Hello. I'm from Macedonia, Europe. I work with a vacuum sputtering machine from ARS. I work with titanium on glass. I'd like to make a mirror with arc sputtering in glass; what metal you think is best?

Florim Osmani
solar glass - Macedonia


October 25, 2012

A. There is no process called "Arc sputtering" that I know of. It is either a cathodic arc or sputtering. Cathodic arc would not be suitable for glass mirrors as the coating would have a rather rough surface. Either sputtering or thermal evaporation would be good. Aluminum is the most common choice for such applications.

H.R. Prabhakara
- Bangalore, India



Can I use stainless steel for 12" dia. primary telescope mirror, and obtain 89% reflection?

November 1, 2014

Q. I recently bought a telescope of 130 aperture with 1000 focal length. know I want to go with a bigger aperture 12" diameter, glass mirrors are very expensive so I thought of stainless steel which will be easier to make in my workshop, so please suggest.

ivan dsouza
machine shop and foundry - Mangalore, Karnataka, India
  ^- Privately contact this inquirer -^


November 2014

A. Hi Ivan. The maximum reflectivity of stainless steel is about 62-64% no matter how well it's polished. Only silver, aluminum, and rhodium offer really high reflectivity in the visible light range. Interestingly, gold has great reflectivity except for that hole in the spectrum which makes it yellow instead of white. Good luck.

Regards,

pic of Ted Mooney Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey

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