Hissing Glass

Oops. I was typing when you and AH were posting. So I didn't see your posts.

Seems like a consensus is building. OMG. Does that mean the debate is over?

No. Give it time. Someone will come along and say it's a vacuum.

Maybe even a new energy source.

No problem...

Pressure differential after closing?

Could be that when opened the ambient temperature drops just a little and when closed again the pressure rises slightly with temperature.

Or... it could be that closing the chamber lid increases the chamber pressure which vents back out over a short time.

Or... maybe a colleague is making a hissing noise behind your back to get your head. Be glad they are not popping a big paper bag like some engineers did to one technician as he was j-u-s-t reaching inside a device to take a measurement.

I'll take a wild guess.

When you open the lid, you let in atmospheric air, which slightly cools the uppermost layer of molten glass. When you close the lid, that "air" becomes superheated and pressurized. The 3 second hiss is the sound of that air escaping.

it is indeed helpful and appreciated.

http://www.pbs.org/programs/journey-to-palomar/

Not only is it timely but it points to an era in this Country when our biggest achievements in Science were funded by private industry not by reckless beurocrats. Everyone should see this, off-topic or not!

"Those who do not know their history are destined to repeat it".

We should be so lucky!

This history you just pointed to restores our pride in what once was and could be again.

Thanks

Laughing Jaguar!

LJ, very kewl hobby you have there!

I'm assuming that you're making Cassegrain telescope mirror blanks, and also assuming you grind/polish/test you're own mirrors?

If so, happy to see another telescope building in our forum! FYI, I've build a few Newtonians in the past, the largest being a 16-inch F4.0.

Love mirror grinding & polishing! It's a good way to relax and release the day's stress!!!

16" is an impressive mirror!

Yeah, it was one heavy monster. It was my 4th Newtonian build. The first one I built was a 8-inch F2.5 when I was 16, many many moons ago!

Anyhow, I now wish I had never sold the 16-incher, but, I need the $$$ to plop down a down payment for the Solar PV system installation on this house!

Someday I'd love to grind a 24-incher.....IF I only can find the time.

I take it you have a good dark site. We do not and I am just too tired of dragging a 10" Mead around.

However, I will pull it out on June 5th for the transit of Venus. I have a nice camera waiting to be mounted to it for that one.

Anon Hero complained: "I am just too tired of dragging a 10" Mead around."

Really?

Stop complaining!

That's 75 pounds of ballast you see, just to balance it! The four saddle bearings weigh 18 pounds a piece!

And this doesn't show the ladder needed to get to the eyepiece which is ten feet off the ground at Zenith!

And your tired?

Laughing Jaguar (and with good reason!)

Ha! Got you beat. :)

Mine is 100+ pounds. It's the Schmidt-Cassegrain LX-200.

Nice Newt. I envy your weight. :)

"However, I will pull it out on June 5th for the transit of Venus. I have a nice camera waiting to be mounted to it for that one."

Let me figure that out:

1. one month to put down the credit card

2. one month to get off the stool

3. One month to dust off the scope, read the manual and set up the scope.

What passion!

It's a good thing it's got computerized tracking. It will find the sun for you!

1. Ah, well, it is long paid for.

2. Stool or pot?

3. Already dusted. We had company last week.

4. This is Florida, everyone knows where the Sun is. :)

Same here. I just finished rebuilding my old 10" Meade Newtonian with a new tube, lightweight mirror cell and Crayford focusser. I've got decent skies where I live, so I have it permanently mounted on a pier in a roll-off roof shed.

It sure is nice to just go out, unlock the roof and roll it open, set the scope to North, flip on the switch and get started.

how about a 600m^2 mirror Check the new HESS telescope in Namibia

my previous job

http://www.mpi-hd.mpg.de/hfm/HESS/pages/about/telescopes/

Of Course! Cold air rushes in; gets trapped under the closed lid; gets hot and then squeezes past the lid seat. Which is a good thing. Can you imagine the consequence of a tightly sealed lid and the air expanding. Entropy where are you when I need you!

Actually the hissing sound is a 20 foot Python I have as a pet. "Honey? Where are the cats?"

No Moose. It won't be a Cass. Life is difficult enough! These are test runs in preparation for two of four new scopes I've designed, all but one with thin meniscus mirrors: 8", 14" and 20"; all are Newtonians. The remaining one is a 14 Inch honeycombed mirror. THAT one has me really excited!

The prior one I opened with, the 8", a thin meniscus mirror, will be slumped later on a mold at 900 degrees; ground and figured to f-3 and then fitted to an all-in-house-made scope. The composite tube was made on my vacuum bench too. This scope is sized to fit into an existing Meade quartz drive fork mount and is airline carry-on legal.

The 14 Inch Meniscus mirrored scope is also a fast f-3 and a modular, also airline legal carry-on.

The 14 inch, honeycombed mirror, also an F-3, will be more of a challenge in that it will take forever to cool after firing; many days me thinks, not counting the annealing phase. The only way to get any volume production is to buy a super large Kiln and stock in the local electric company!

*

When installed in a scope, this mirror will reach thermal equilibrium five times faster by virtue of the reduced mass and increased surface area. That's the whole idea for honeycombing an otherwise solid blank. However, thin slumped meniscus mirrors are showing lots of promise and may obviate the complex production process needed to produce honeycombs. The purists want honeycomb however so.......................!

By contrast, these thin meniscus mirrors are a piece of cake to make. Given the temps, maybe I should say a piece of pizza!

After all that, it's nothing but hot air (sic!)

. . . . . . the hissing sound of course!

Thanks all, for the responses.

L.J.

allowing air to enter the kiln by opening the door will introduce contaminants that will activate the flux and cause the hizzing sound. i'm not familar with the process of making optical glass, but i'm thinking that by injecting an inert gas into the kiln under very low pressure would make a dramatic difference in clarity.

DurtieDuck wrote: ". . . .contaminants that will activate the flux. . . . "

I am making mirror blanks. There is no flux. What for?

DurtieDuck wrote: ". . . . . inert gas into the kiln under very low pressure would make a dramatic difference in clarity."

Huh? No it won't. They will get ground, polished and figured as mirrors. These are borosilicate and float glass blanks for first surface mirrors, not lenses.

L.J.

ahh, now you went and hurt my feelings. i guess i'll just have to kick the dog to make me feel better.

Durtieduck wrote: "ahh, now you went and hurt my feelings"

That was not my intention. . . . . You were simply trying to solve a problem that you thought existed but didn't.

"I guess i'll just have to kick the dog to make me feel better."

Don't you dare!

When you stop trying to solve problems, that pooch will still love you, with or without a can opener!

L.J.

Great blog, telescopes and RC aircraft, couldn't be better!!

It's caused by the sand which the glass is made from:

http://en.wikipedia.org/wiki/Singing_sand