Aloha group,
I live on Hawaii's Big Island and exposed to a very corrosive atmosphere (SO2/H2SO4 primarily). My 20" mirror needs recoating very frequently, and I am looking for a cost-effective alternative to constantly shipping it to the mainland coaters. I am not very knowlegable about details of vacuum coating, nor have the time to build, or funds to buy, a sophisticated apparatus.

My question is: Would it be practical to make a "simple" vacuum apparatus to achieve a useable Al coating even if the coating comes out "below commercial standards" due to insufficient vacuum, etc.? That may not be so bad, since I need to recoat it anyway every few months. I would appreciate any advice as to whether such an approach is worth pursuing for my unique situation?

Thank you!
Mike




------------------------------------

Yahoo! Groups Links

?

Aloha group,
I live on Hawaii's Big Island and exposed to a very corrosive atmosphere (SO2/H2SO4 primarily). My 20" mirror needs recoating very frequently, and I am looking for a cost-effective alternative to constantly shipping it to the mainland coaters. I am not very knowlegable about details of vacuum coating, nor have the time to build, or funds to buy, a sophisticated apparatus.

My question is: Would it be practical to make a "simple" vacuum apparatus to achieve a useable Al coating even if the coating comes out "below commercial standards" due to insufficient vacuum, etc.? That may not be so bad, since I need to recoat it anyway every few months. I would appreciate any advice as to whether such an approach is worth pursuing for my unique situation?

Thank you!
Mike

?

?

?

Guy,

What do you mean: "when I close connection between the mechanical pump and the diffusion pump"? If you close backing valve and open gate valve, system won't work.? Only cryo and other sorption pumps work with closed backing valve. Dif and turbo pumps must be backed always.

Do you have gauge on the dif pump input flange under the gate valve and on its output? What are the pressures?

Sometimes valves may leak in some position, for instance, there is no leak when it closed and a great leak when it opened. So everything looks fine when a gate valve is closed, and a big leak appears when you open it for high vacuum pumping.

Best regards,

Vladimir

On 12/26/2010 12:48 AM, Guy Brandenburg wrote:

Our old no-name, government-surplus diffusion pump has a problem.?

After pumping the diff pump for a while (minutes or hours, doesn't seem to make a difference) and after loading the mirror to be coated into the bell jar, this is what happens:

when I close the connection between the mechanical pump and the diffusion pump, and begin pumping down the bell jar directly, the pressure in the diffusion pump all of a sudden rises dramatically, going up to ~200 millibars if I don't immediately switch back to pumping down the diffusion pump directly again. It becomes quite a dance, closing one valve then opening the other, then reversing again, and again, and again.

Eventually it always settles down and I get decent vacuum levels, but it's annoying for a while.
?

Guy Brandenburg, Washington, DC?

My blog, mostly on Education in DC:

My home page on astronomy, mathematics, education:

or else ??

=====================================

Our old no-name, government-surplus diffusion pump has a problem.?

After pumping the diff pump for a while (minutes or hours, doesn't seem to make a difference) and after loading the mirror to be coated into the bell jar, this is what happens:

when I close the connection between the mechanical pump and the diffusion pump, and begin pumping down the bell jar directly, the pressure in the diffusion pump all of a sudden rises dramatically, going up to ~200 millibars if I don't immediately switch back to pumping down the diffusion pump directly again. It becomes quite a dance, closing one valve then opening the other, then reversing again, and again, and again.

Eventually it always settles down and I get decent vacuum levels, but it's annoying for a while.
?

Guy Brandenburg, Washington, DC?

My blog, mostly on Education in DC:

My home page on astronomy, mathematics, education:

or else ??

=====================================

?

Hi,

?

this seems very weird, I dont understand!! 200 mb is very high. Can you pump the bell jar down without bypassing the diff pump? what happens then? Because you can achieve a good final vacuum (how much?), there cant be too much wrong with your system, I wonder if there is someting wrong with the gauge(s), I've seen some pirani gauges do stupid things when they have been contaminated,

?

sorry this is not much use, but just my ramblings,

?

?

James

----- Original Message -----

From: Guy Brandenburg

To: VacuumX@...

Sent: Sunday, December 26, 2010 8:48 AM

Subject: [VacuumX] weird diffusion pump behavior

?

Our old no-name, government-surplus diffusion pump has a problem.?

After pumping the diff pump for a while (minutes or hours, doesn't seem to make a difference) and after loading the mirror to be coated into the bell jar, this is what happens:

when I close the connection between the mechanical pump and the diffusion pump, and begin pumping down the bell jar directly, the pressure in the diffusion pump all of a sudden rises dramatically, going up to ~200 millibars if I don't immediately switch back to pumping down the diffusion pump directly again. It becomes quite a dance, closing one valve then opening the other, then reversing again, and again, and again.

Eventually it always settles down and I get decent vacuum levels, but it's annoying for a while.
?

Guy Brandenburg, Washington, DC?

My blog, mostly on Education in DC:

My home page on astronomy, mathematics, education:

or else ??

=====================================

?

Just a guess, but that sort of behavior has been linked to a weak
heater on the diff pump.
The pump oscillates between backstreaming and proper behavior.

It's a long shot, but it's been known to happen...

Daryl

----- Original Message -----

From: Guy Brandenburg

To: VacuumX@...

Sent: Sunday, December 26, 2010 8:48 AM

Subject: [VacuumX] weird diffusion pump behavior

?

Our old no-name, government-surplus diffusion pump has a problem.?

After pumping the diff pump for a while (minutes or hours, doesn't seem to make a difference) and after loading the mirror to be coated into the bell jar, this is what happens:

when I close the connection between the mechanical pump and the diffusion pump, and begin pumping down the bell jar directly, the pressure in the diffusion pump all of a sudden rises dramatically, going up to ~200 millibars if I don't immediately switch back to pumping down the diffusion pump directly again. It becomes quite a dance, closing one valve then opening the other, then reversing again, and again, and again.

Eventually it always settles down and I get decent vacuum levels, but it's annoying for a while.
?

Guy Brandenburg, Washington, DC?

My blog, mostly on Education in DC:

My home page on astronomy, mathematics, education:

or else ??

=====================================

Yes, indeed, lots of variables. What do YOU use for the final drying, Vladimir?
?

Guy Brandenburg, Washington, DC?

My blog, mostly on Education in DC:

My home page on astronomy, mathematics, education:

or else ??

=====================================

---

From: Vladimir Chutko
To: VacuumX@...
Sent: Fri, October 22, 2010 11:54:38 PM
Subject: Re: [VacuumX] final drying of mirror before coating

?

Hi Guy,

There are too many possible causes of that "weird residue": old glass surface, bad cleaning (both wrong materials and bad hands), bad vacuum quality, wrong ion cleaning.... What kind of glass do you use? What is a time gap between polishing and coating? A regular? cleaning with alcohol or acetone using special paper napkins (I can give you a brand next week) or just washed fat free cotton ones usually provide a surface well suitable for Al coating. Of coarse, glow discharge or ion beam pre-cleaning in vacuum is necessary. If you use glow discharge, a working gas actually doesn't matter, you can use even air; if you use ion source, gases (Ar, O2, N, or their mixes) must be very pure. And vacuum quality - oil free ultimate vacuum about 10-5 torr required.

The source(s) of those defects may be in any process step. It is hard to discuss without detailed information about all of them....

Regards,

Vladimir Chutko



On 10/22/2010 8:09 PM, Guy Brandenburg wrote:

Question to all:?

How do you perform your final mirror-drying operation before putting that sucker into your backyard or basement vacuum chamber?

In our plain-vanilla mirror-coating operation at the NCA-CCCC telescope-making and mirror-coating and nose-picking workshop here in DC, which I 'inherited' from a previous leader, I think that I am finding recently that there is some sort of weird residue on sections of a number of newly coated mirrors - coated by us.?

I suspect that it seems to come off of paper towels - at least some brands of them, I suspect. Unfortunately, I have not done a systematic evaluation to see if this is true, and the conditions are always just a little bit different every time I coat or re-coat a mirror. So I am really not sure on this at all, one way or the other. I have no idea whether it's the final rinsing that's inadequate, or if it's something in certain brands and varieties of paper towels themselves, or something else. I avoid types that advertize hand-softeners or anything like that. Sometimes I wonder whether I forgot and blew my nose on the paper towels first. Or maybe the Green River wasn't mixed properly. Or perhaps these mirrors just have cooties?Or perchance the ion bombardment (aka glow discharge) wasn't long enough. Or I'm just an idiot. Etcetera. In any case, I don't recall seeing it much before, and it seems to be getting worse. (but even that data point is suspect.)

BTW, the setup that we have is something that was scrounged together from 1950-to-1960-era US government surplus equipment coupled with a variety of modifications and improvements that were crafted by my predecessors, or donated by others. My predecessors are mostly either deceased or are in poor health. We do this aluminization for purely nominal fees that allow us to buy some more pitch and grit and glass.

(The mirrors are certainly usable, but they are not elegantly clean like I would prefer. You can see thin, dusty streaks when you look at the mirror at certain angles.?I know, I know, I should have taken a picture. Will do so.

(But the workshop location is clear on the other side of town. And when I'm there, unless I go on off-hours, there are always lots of folks building telescopes at one level or another, and they all have questions or need advice. So I don't get to do much for myself. And they are closed on Sundays, and normal closing time is 10 PM.)

I have read and heard of lots of ways of doing this final drying, including distilled water blown off by compressed nitrogen; pure ethanol; pure this, pure that, microfibers, and more. ?

What methods are preferred by the present readership?
?

Guy Brandenburg, Washington, DC?

My blog, mostly on Education in DC:

My home page on astronomy, mathematics, education:

or else ??

=====================================

Vladimir,

Could you tell me the purity degree or lever the O2 and Ar gas you use!

Thank's!

Attila
The Hun

--- In VacuumX@..., Vladimir Chutko<chutko@...> wrote:

Hi Guy,

There are too many possible causes of that "weird residue": old glass
surface, bad cleaning (both wrong materials and bad hands), bad vacuum
quality, wrong ion cleaning.... What kind of glass do you use? What is a
time gap between polishing and coating? A regular cleaning with alcohol
or acetone using special paper napkins (I can give you a brand next
week) or just washed fat free cotton ones usually provide a surface well
suitable for Al coating. Of coarse, glow discharge or ion beam
pre-cleaning in vacuum is necessary. If you use glow discharge, a
working gas actually doesn't matter, you can use even air; if you use
ion source, gases (Ar, O2, N, or their mixes) must be very pure. And
vacuum quality - oil free ultimate vacuum about 10-5 torr required.

The source(s) of those defects may be in any process step. It is hard to
discuss without detailed information about all of them....

Regards,

Vladimir Chutko



On 10/22/2010 8:09 PM, Guy Brandenburg wrote:

Question to all:

How do you perform your final mirror-drying operation before putting
that sucker into your backyard or basement vacuum chamber?

In our plain-vanilla mirror-coating operation at the NCA-CCCC
telescope-making and mirror-coating and nose-picking workshop here in
DC, which I 'inherited' from a previous leader, I think that I am
finding recently that there is some sort of weird residue on sections
of a number of newly coated mirrors - coated by us.

I suspect that it seems to come off of paper towels - at least some
brands of them, I suspect. Unfortunately, I have not done a systematic
evaluation to see if this is true, and the conditions are always just
a little bit different every time I coat or re-coat a mirror. So I am
really not sure on this at all, one way or the other. I have no idea
whether it's the final rinsing that's inadequate, or if it's something
in certain brands and varieties of paper towels themselves, or
something else. I avoid types that advertize hand-softeners or
anything like that. Sometimes I wonder whether I forgot and blew my
nose on the paper towels first. Or maybe the Green River wasn't mixed
properly. Or perhaps these mirrors just have cooties?Or perchance the
ion bombardment (aka glow discharge) wasn't long enough. Or I'm just
an idiot. Etcetera. In any case, I don't recall seeing it much before,
and it seems to be getting worse. (but even that data point is suspect.)

BTW, the setup that we have is something that was scrounged together
from 1950-to-1960-era US government surplus equipment coupled with a
variety of modifications and improvements that were crafted by my
predecessors, or donated by others. My predecessors are mostly either
deceased or are in poor health. We do this aluminization for purely
nominal fees that allow us to buy some more pitch and grit and glass.

/(The mirrors are certainly usable, but they are not elegantly clean
like I would prefer. You can see thin, dusty streaks when you look at
the mirror at certain angles. I know, I know, I should have taken a
picture. Will do so./
/
/
/(But the workshop location is clear on the other side of town. And
when I'm there, unless I go on off-hours, there are always lots of
folks building telescopes at one level or another, and they all have
questions or need advice. So I don't get to do much for myself. And
they are closed on Sundays, and normal closing time is 10 PM.)/

I have read and heard of lots of ways of doing this final drying,
including distilled water blown off by compressed nitrogen; pure
ethanol; pure this, pure that, microfibers, and more.

What methods are preferred by the present readership?
Guy Brandenburg, Washington, DC

My blog, mostly on Education in DC:



My home page on astronomy, mathematics, education:

<>
or else

=====================================

------------------------------------

Yahoo! Groups Links

Can't find any pix after an extensive 9-second search. Will take some later on
this week.
Guy Brandenburg, Washington, DC