Return to the Cloudy Nights Telescope Reviews home pageAstronomics discounts for Cloudy Nights members
· Get a Cloudy Nights T-Shirt · Submit a Review / Article

Click here if you are having trouble logging into the forums

Privacy Policy | Please read our Terms of Service | Signup and Troubleshooting FAQ | Problems? PM a Red or a Green Gu… uh, User

Equipment Discussions >> ATM, Optics and DIY Forum

Pages: 1
sopticals
professor emeritus


Reged: 03/28/10

Loc: New Zealand
Laminated mirrors in use, anyone? new
      #5625216 - 01/15/13 09:18 PM

Anyone out there, that has successfully made a decent mirror, using two or more discs of glass laminated together? If so, what bonding material was used? Thanks in advance.

Stephen. (44deg.S)


Post Extras: Print Post   Remind Me!   Notify Moderator  
sopticals
professor emeritus


Reged: 03/28/10

Loc: New Zealand
Re: Laminated mirrors in use, anyone? new [Re: sopticals]
      #5626886 - 01/16/13 07:55 PM

Must be someone out there? Im sure on a similar thread in the past there was at least one person that claimed to be using a successful laminated mirror.

Edited by sopticals (01/16/13 07:56 PM)


Post Extras: Print Post   Remind Me!   Notify Moderator  
starman345
Wait, I'm Thinking
*****

Reged: 07/06/10

Loc: New Brunswick, Canada
Re: Laminated mirrors in use, anyone? new [Re: sopticals]
      #5626909 - 01/16/13 08:06 PM

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

Post Extras: Print Post   Remind Me!   Notify Moderator  
careysub
Carpal Tunnel
*****

Reged: 02/18/11

Loc: Rancho Cucamonga, CA
Re: Laminated mirrors in use, anyone? new [Re: sopticals]
      #5627125 - 01/16/13 10:12 PM

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 and low outgassing. The CTE is advertised to be 12e-6 /C and the shrinkage is supposed to be 0.02%. I'm interested in it to bond two zerodur pieces together for our secondary mirror. "


Post Extras: Print Post   Remind Me!   Notify Moderator  
sopticals
professor emeritus


Reged: 03/28/10

Loc: New Zealand
Re: Laminated mirrors in use, anyone? new [Re: starman345]
      #5627358 - 01/17/13 02:13 AM

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: Print Post   Remind Me!   Notify Moderator  
sopticals
professor emeritus


Reged: 03/28/10

Loc: New Zealand
Re: Laminated mirrors in use, anyone? [Re: careysub]
      #5628505 - 01/17/13 05:22 PM

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: Print Post   Remind Me!   Notify Moderator  
Ajohn
sage
*****

Reged: 12/03/07

Re: Laminated mirrors in use, anyone? new [Re: sopticals]
      #5638294 - 01/23/13 06:26 AM

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: Print Post   Remind Me!   Notify Moderator  
careysub
Carpal Tunnel
*****

Reged: 02/18/11

Loc: Rancho Cucamonga, CA
Re: Laminated mirrors in use, anyone? new [Re: Ajohn]
      #5638741 - 01/23/13 11:35 AM

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
-




How about simply making the entire back out of a big bundle of tubing fused/cemented together?


Post Extras: Print Post   Remind Me!   Notify Moderator  
careysub
Carpal Tunnel
*****

Reged: 02/18/11

Loc: Rancho Cucamonga, CA
Re: Laminated mirrors in use, anyone? new [Re: Ajohn]
      #5638872 - 01/23/13 12:51 PM

How about this idea to provide the entire backing of the thin mirror:

Stack Pyrex tubes in a hexagonal grid touching each other with an adhesive binder (epoxy say) that either does not change dimensions at all or shrinks slightly as it sets. Epoxy normally shrinks as it sets/cures, if the usual amount is too much this can be controlled and no-shrink epoxy is available. Other resins/binders can be used of course.

As the mirror cools below the binder curing temperature the Pyrex (CTE 3.3x10^-6/K) will not shrink much; the binder (if regular epoxy CTE 55x10^-6 or thereabouts) will shrink much more and put itself under tension.

But the tubing is in a maximum density space-filling configuration so it cannot pack more tightly together, there is no change in area of the grid other than that due to the glass tubing contraction, matching that of the mirror optical surface.


Edited by careysub (01/23/13 09:07 PM)


Post Extras: Print Post   Remind Me!   Notify Moderator  
Pages: 1


Extra information
9 registered and 24 anonymous users are browsing this forum.

Moderator:  ausastronomer, richard7, Starman81 

Print Thread

Forum Permissions
      You cannot start new topics
      You cannot reply to topics
      HTML is disabled
      UBBCode is enabled


Thread views: 824

Jump to

CN Forums Home


Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics