Hello, need a really large piece of glass for a project and am hoping you all could help.

 

Also, I would prefer for the sheet to be made from Pyrex glass. Thank you

Edited February 11, 20178 yr by Wil242424

Your local glass company?

If they can't get it for you, they can probably tell you who can.

"Large"? "Really large"?! If this is a science project, start being more precise right now.

 

And don't you mean 5 millimeters? I don't think bulletproof glass is 5 inches thick.

 

So you need a big size sheet of pyrex, and places like Amazon and Alibaba can't help you?

Okay, I need a 35 inch by 5 inch thick circle of Pyrex glass. And it is not an attempt to make something bullet proof. I was only not being very specific because I can make due with any piece of Pyrex glass that is 35+ inches by 35+ inches by 5 inches thick. The problem that I seem to find is that no supplier makes these sheets at that thickness.

Edited February 12, 20178 yr by Wil242424

Can you make do with 10 pieces that are 12mm thick?

- If you are at a university, chances are your university has a glass workshop somewhere hidden in a basement: ask them.

 

- ask local glass company

 

- why does it need to be that thick? Strength? optical properties? heat transfer?

The seller here includes a copy of n invoice from a company that sold a blank about half that size...
http://www.ebay.co.uk/itm/like/122342866851?lpid=122&chn=ps&adgroupid=41285909471&rlsatarget=pla-278687415243&adtype=pla&poi=&googleloc=1007064&device=c&campaignid=738225731&crdt=0
Casting a thick glass block is not a simple issue. It takes a long time- weeks- in the oven slowly cooling.

http://atomictoasters.com/2011/11/making-the-200-inch-mirror-for-the-hale-telescope/

What do you want it for?

There may be a simpler option.

Edited February 12, 20178 yr by John Cuthber

I need the glass for a telescope primary mirror. It needs to be that thick so it is not distorted when exposed to different temperatures.

Unless you have a lot of spare money, you are not going to succeed.

Unless you have a lot of spare money, you are not going to succeed.

Probably a second mortgage.

 

I need the glass for a telescope primary mirror. It needs to be that thick so it is not distorted when exposed to different temperatures.

How about using an inch of glass and 4 inches of suitable metal.

I need the glass for a telescope primary mirror. It needs to be that thick so it is not distorted when exposed to different temperatures.

Are you sure there is no other way to go round this problem? Making pure glass that thick is high technology.

 

For example avoiding the different temperatures?

Or using an algorithm for image correction depending on temperature?

I guess that a problem even greater than this one is that of making a parabolic surface of an accuracy which makes the project sensible. Plus the question of how to make the reflecting surface. I would be interested in having further details about this.

I would guess that large telescope mirror blanks are specialty items, and that contacting telescope makers/suppliers would be a reasonable course of action.

 

e.g.

Advanced Glass says they will make one up to 40" but doesn't mention thickness

http://www.advancedglass.net/products/monolithic_telescope_mirror_blanks.html

 

United Lens says they will do custom work

https://www.unitedlens.com/test-plates-mirror-blanks/

 

Newport Glass has a 32" x 3.5" blank as a standard part and say they do custom jobs

http://www.newportglass.com/angwcat.htm (click on standard pyrex mirror blanks)

I wouldn't be surprised that buying a telescope would be cheaper than having such a mirror custom made. I have no idea how big a telescope you can buy on the market, though.

I wouldn't be surprised that buying a telescope would be cheaper than having such a mirror custom made. I have no idea how big a telescope you can buy on the market, though.

I couldn't find the link now but there was a 48-incher for sale.

Just so you all know, I am not looking for a telescope mirror of that size. I am looking for a piece of glass which I can shape and make into a mirror.

What accuracy do you need?

If it's for a searchlight or a sun concentrator you can put up with much worse precision.

If you tell us what you are trying to do we can probably help.

Otherwise this might cost a lot more than it needs to.

Just so you all know, I am not looking for a telescope mirror of that size. I am looking for a piece of glass which I can shape and make into a mirror.

I am interested to learn how you are going to do it? Manually? I know how that precise convex lens can be prepared and polished manually (although not exactly up to that size, I believe), but how do you make concave shape?

Spherical should be doable, but with the aberrations, he shouldn't care about any distortions due to the thickness of the glass.

 

For a parabolic mirror, you can melt the glass and cool it down while rotating, so you only need the raw material.

 

Still, I'm also interested in the technique he is going to use (which will help determining the requirements).

For a parabolic mirror, you can melt the glass and cool it down while rotating, so you only need the raw material.

 

 

But this process requires immense investment in machinery - I understand that the cooling down can take several years, while the glass is rotating at a precise rate without vibration.

I guess it depends on the required thickness and accuracy. I have no experience with this whatsoever, but if I had to make a mirror that size, I would consider doing something like that to have a rough shape before grinding it more precisely.

Well, I could build a rotating kiln- but I can't help thinking that using a mould to get roughly the right shape would be easier.

 

However, until the OP tells us what he's actually aiming for, there's not a lot of point speculating.

To give a basic idea of how I am thinking of shaping the glass here is a link: https://stellafane.org/tm/atm/

 

Of course, this process with take lots and lots of time.

Just so you all know, I am not looking for a telescope mirror of that size. I am looking for a piece of glass which I can shape and make into a mirror.

That's what a mirror blank is.

To give a basic idea of how I am thinking of shaping the glass here is a link: https://stellafane.org/tm/atm/

 

Of course, this process with take lots and lots of time.

Interesting.

 

Do keep in mind that you want to manipulate 50+ kg.

They state a 6" mirror would take 40-80 hours, since your mirror is about 6 times larger, you need to remove 200 times more material, so you might be looking at 8000 hours.