replacing, gluing new mirror onto SLR

David Lyga · Oct 16, 2019

Oftentimes I have had occasion to paste a new mirror onto an SLR. However, this time I have failed. I think that the problem is that both the mirror and the metal plate (which it gets glued to) are non-porous. Thus, my Gorilla Glue's brittleness has allowed the new mirror to come loose after a hundred or so exposures.

My question is this: I have noticed that the glue used for most SLR mirrors is never really brittle; it seems to dry with a very slight texture which yields somewhat when a very sharp object, like a tiny screwdriver, probes it. Which type of readily available glue will dry to this non-brittle consistency? Am I correct with my assumptions here?

I even have tried to use transfer tape, but the hold is not that strong. This seems to be a relatively simple query, but I am a bit dumbfounded. - David Lyga

AgX · Oct 16, 2019

What is Gorilla Glue? Please specify as there are several cements under that brand.

Not every cement needs a rough surface. But that surface must be clean, more so the more smooth it is. Some cements as cyanacrylates need moisture to cure. Such will not work if the ratio of area to slit width is too big and the surfaces are gas tight and there is no moisture caught at the surfaces.

David Lyga · Oct 16, 2019

The VERY FAMOUS glue is actually (I think) made in Sweden. It is sold everywhere in the USA. See here: https://www.gorillatough.com/products/

I use the white, (not clear) one.

This is more accurate: https://www.gorillatough.com/products/#filter=.gorilla-glue

However, you might be right: I did NOT use any water with this glue and that might be one of the problems.

AgX · Oct 16, 2019

I know quite some people love cyanacrylates and they are used massively at the industry. But I dislike it. I use it to cement a torn fingernail, but hardly ever at my workshop.

Kino · Oct 16, 2019

I would use a thin layer of JB Weld or 2-part epoxy myself, but I don't know how flexible the adhesive would remain...

AgX · Oct 16, 2019

In such cases the advantage of cyanacrylate cements is that for sure they do not add substantial film thickness. Imagine handling very fast curing epoxy. You easily end at a stage were that stuff is becoming viscous at a location where one not even may use much pressure.

reddesert · Oct 16, 2019

Maybe try a contact cement like Pliobond.

I don't like Gorilla Glue for a lot of applications because it expands as it cures. This is good for some uses but bad for others.

John Koehrer · Oct 16, 2019

reddesert said:
Maybe try a contact cement like Pliobond.

A standard of camera repairmen(women) everywhere.

Truzi · Oct 16, 2019

Pliobond came to my mind too. I would think something like contact/rubber cement would be good as it can be undone if needed.
How about Hide Glue? I've never used it, so don't know how appropriate it would be.

AgX · Oct 17, 2019

Could be undone, but not on a mirror cemented full area and still installed. Furthermore, at classic application the mirror would get out of alignement.

Nodda Duma · Oct 17, 2019

David,

Use silicone RTV to bond the mirror in place. This will sound strange, but I’m talking like silicone caulking stuff like what you use for household repairs. The clear or white all-weather adhesive or sealing RTV would be best. Clean surfaces with alcohol — the cleaner the better, then apply just enough to mount the mirror on the frame. Don’t use too little but don’t goop it on either.

Let set for the requisite 24 hours.

You should be able to find some in a smaller tube at your local hardware store.

Rick A · Oct 17, 2019

David, I think a two part urethane adhesive would work best for your application. One part urethanes rely on moisture for curing, which could cause foaming and expansion. Two part adhesive is a chemical bond much like epoxy, but remains slightly more flexible. Look at 3M products such as this:
https://www.amazon.com/3M-Scotch-Weld-Composite-Urethane-Adhesive/dp/B07Q28D89C

David Lyga · Oct 17, 2019

Thank you for the plethora of replies. I am surprised that this topic did not come up before (maybe it did). It is not so 'esoteric' for a mirror to need replacement and I think that these responses will help more than me. Again, thanks. - David Lyga

ic-racer · Oct 23, 2019

I was doing some repairs on a FX-3 Yashica today and noticed this. Seems the mirror is held on with tape. #3 in the picture is listed as "Mirror Tape."

Kino · Oct 24, 2019

3M makes some very strong double sided tape that is used in automotive and aircraft industries; that might do the trick:

https://www.amazon.com/3M-3614-15/dp/B002JOVUO0?tag=polaroidfotobar-20

Only thing is, I am unsure as to it's thickness...

Ray Morgenweck · Oct 24, 2019

I’ve used weld wood contact cement many times with similar materials. Two coats, dry to the touch, then press firmly in position.

David Lyga · Oct 25, 2019

Yes, I already knew about the tape. But what I did was simple and this really works. Gorilla glue is supposed to be applied with a bit of water. I did not know how profound that directive really was, so I did just that. The bond is inseparable now.

The problem with the mounting tape is that it has a considerable thickness. THAT will modify the precise alignment of the mirror and might cause VF focus to be a bit differently from REAL (film plane) focus. I take no chances. And the amount of Gorilla glue (with water) I applied was minuscule, thus no expansion worries. - David Lyga

replacing, gluing new mirror onto SLR

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