Quote:

---

Stephen, are you thinking of adding a layer to your 25" mirror, or is this a new project you are thinking about?

---

Hi Brian,

Looking at a new project. Have finished the 25". Will be silvering it myself in a few weeks time, when we in the Southern Hemisphere, get some dark sky back, when summers gone. May actually silver one of my 22"ers first though as it will be easier to manage as a first time (for me) silvering.

Stephen.(44deg.S.)

Edited by sopticals (01/17/13 02:16 AM)

Post Extras:

Quote:

---

This thread:
http://www.cloudynights.com/ubbthreads/showflat.php/Cat/0/Number/3828920/Main...

Has this:
"One epoxy I've had my eye on is Masterbond EP30LTE-LO. This is a low CTE epoxy with low shrinkage

---

Hi Careysub,

Thanks for the input. Have been in contact with Masterbond, and looking globally for suitable glass bond substances with the right CTE. Not concerned about the out gassing issue, as I will be silvering.

Stephen.(44deg.S.)

Post Extras:

Quote:

---

There used to be some small cemented apo refractors about but I understand that the size was limited to under 3ins due to shrinkage of the cement deforming the glass. Also as sizes go up differential expansion rates breaking the bond.

It's a subject that interests me as I like the idea of a glass disc that is more or less self supporting. One idea I have which may work out is to grind a series of pockets into 2 discs made out of the same glass and bond them together with "pegs" leaving a space in between the discs. It might be possible to make the pegs out of borosilicate laboratory tubing for instance. Problem - what to use to bore the holes in the glass discs and how thick could the the bonding be?

I feel that this could result in a very rigid light weight structure that could reach the same levels of performance as old style full thickness blanks.

John
-

---

Post Extras: