How to glue mirrors to mirror mounts
Brian Greenstone
glue a mirror to a mirror mount? Is there some kind of special glue, or do
you use epoxy? Are these things usually permanently mounted or is there a
way to unmount a mirror once it's glued on?
Thanks-
-Brian
L. Michael Roberts
I use standard 'transparent' bathroom silicone from Home Depot. I
have found that 'superglue' becomes brittle over time and 5 minute
epoxy is almost impossible to remove. A thin layer of silicone
allows thermal expansion and can be removed with a razor blade when
the optic needs changing [although this usually breaks thin
mirrors]. This is not an expert opinion - your needs may differ
depending on how critical the application is.
+==================== L. Michael Roberts =======================+
This represents my personal opinion and NOT Company policy
Hamilton, Ont, Canada. To reply, post a request for my valid E-mail
"Life is a sexually transmitted, terminal, condition"
+=================================================================+
Bob May
reason for this is that a very rigid connection between the two will stress
the mirror to an incorrect shape before the problems of seperation due to
overstressing the joint. For larger mirrors, 3 dots of silicone adhesive at
about the 50% radius (the old theory was about 70% of the radius) is about
the right place to put the adhesive. For smaller mirrors, a single dab is
usually sufficient if it's a significant part of the back.
--
Bob May
Remember that computers do exactly what you tell them to do, not what you
think you told them to do.
P. Danek
environment. We like using the Duco because you can remove the optic if
you want to without damaging it.
I just got a sample of Norland UV curable cement from Thor Labs.
Haven't tried it yet but if you call them you might be able to get a
free bottle, www.thorlabs.com.
P. Danek
Brian Greenstone
wrote on 9/20/01 4:35 PM:
I'm doing holography in my lab, so I'm concerned that a flexible glue might
not be stable enough. I need to keep things rigid, and vibration free.
-Brian
L. Michael Roberts
In that case the thin layer of cheap silicone [or 3 small dots]
would probably be your best option unless you want to spend lost of
$$$ on fancy optical epoxy.
P. Danek
shrink as it dries as that is what causes the warping.
P. Danek
Steve Eckhardt
>Brian Greenstone wrote:
>>
>> This is probably a really stupid question, but I'm new at this. How do you
>> glue a mirror to a mirror mount? Is there some kind of special glue, or do
>> you use epoxy? Are these things usually permanently mounted or is there a
>> way to unmount a mirror once it's glued on?
>>
>> Thanks-
>> -Brian
At 3M, we use tape. (surprised?) I don't know if it's appropriate for
holography, though. I would recommend a silicone or rubber based glue because
you really don't want your mirror to be warped by thermal expansion. (Aluminum
absorbs 12% of the light, but laser high reflectance coatings would be
superior.) The amount of creep in a thin layer of silicone should not be a
problem.
--
Best regards,
Steve Eckhardt (skeck...@mmm.com)
Opinions expressed herein are my own and may not represent those of my employer.
The Scheuchs
by 3M. At Labsphere we did some reliability testing and now use one of
these products to mount all of our mirrors. I'm not sure of the exact
product number, but the tape is thin and therefore causes minimal offset of
the mirror from the front surface of the mirror mount. There is no curing
time. This is a VERY permanent mounting method.
Jonathan Scheuch
Labsphere
Brian Greenstone wrote in message ...
Bob May
mirror. Rigid mountings will end up causing stress on the mirror as the
temp changes (and it doesn't need to change very much!) although if you are
just using a very small part of the mirror for the actual reflection, that
won't be too much of a problem.
Another poster mentioned doublesided sticky tape and that's also quite good.
You do really need some flexibility so that the mirror won't be stressed by
it's mount. Also note that you don't need much contact to hold a mirror in
place and thinner sections will be quite enough for small stuff. I
recommend that an 8" mirror an inch thick use a spacing of about the
thickness of a quarter or two for best results and the diameter of the dots
to be about the diameter of a dime to penny in size.
Louis Boyd
>
> in article tqko8v7...@corp.supernews.com, Bob May at bob...@nethere.com
> wrote on 9/20/01 4:35 PM:
>
> > You want to use a flexible glue to attach a mirror to a backing plate. The
> > reason for this is that a very rigid connection between the two will stress
> > the mirror to an incorrect shape before the problems of seperation due to
> > overstressing the joint. For larger mirrors, 3 dots of silicone adhesive at
> > about the 50% radius (the old theory was about 70% of the radius) is about
> > the right place to put the adhesive. For smaller mirrors, a single dab is
> > usually sufficient if it's a significant part of the back.
>
> not be stable enough. I need to keep things rigid, and vibration free.
Bob's advice about silicon adhesive is reasonable for many uses. Beside
that, making a mirror cell out of a material with as similar of thermal
expansion to the mirror substrate helps maintain stabilty and reduce the
stress on the adhesive (which also gets applied to mirror). Invar or a
low expansion ceramic is usually the best choice for a mirror mount
though they're expensive. Cast iron has one of the lowest thermal
expansion coefficients of common inexpensive metals and it's easy to
machine. Aluminum is about 2.5 times worse.
A mirror doesn't have to be glued at all. It can can be accurately held
in alignment with as few as three hard points. For a small disk mirror
standing "on edge" a three point mount on the mirrors circumference,
centered on the edges (none on the back) will provide minimum
distortion if the pressure on the points is moderate.
Even the strongest metals and low expansion glass aren't infinitely
rigid. In fact they are quite elastic over a small range of motion. A
thin layer of adhesive can work as a dampener to reduce vibration.
Whether glue is used or not you have to deal with flexibility in the
system. Mirrors will only vibrate if subject to variable force, such as
shaking the table or air currents.
--
Lou Boyd
Fairborn Observatory
Joe Gwinn
<bob...@nethere.com> wrote:
> The secret here is the fight between rigidity and stress applied to the
> mirror. Rigid mountings will end up causing stress on the mirror as the
> temp changes (and it doesn't need to change very much!) although if you are
> just using a very small part of the mirror for the actual reflection, that
> won't be too much of a problem.
> Another poster mentioned doublesided sticky tape and that's also quite good.
> You do really need some flexibility so that the mirror won't be stressed by
> it's mount. Also note that you don't need much contact to hold a mirror in
> place and thinner sections will be quite enough for small stuff. I
> recommend that an 8" mirror an inch thick use a spacing of about the
> thickness of a quarter or two for best results and the diameter of the dots
> to be about the diameter of a dime to penny in size.
I would add that it's a bad idea to make the silicone rubber too thin,
because the thinner the rubber layer the higher the strain in the rubber
as the temperature changes and the glass moves relative to the mount (made
of aluminium?). Even the difference between daytime and nightime inside a
building can do it. If the strain is too high, the rubber will soon fail,
and the mirror will be able to move around, or even to fall off. The
larger the mirror diameter, the thicker the silicone layer must be. That
said, silicon rubber will tolerate 200% strain (pull to double the length)
acutely, and perhaps 20% for long periods and/or many reversing stress
cycles, if memory serves. See the datasheet and application notes for the
details.
I found this out the hard way fifteen or twenty years ago, when we had
polycarbonate tops just popping off of an instrument with an aluminium
chassis, despite the fact that to pull the top off at first took hundreds
of pounds of applied force. The low-tech solution was little pieces of
toothpick embedded in the wet rubber before pushing the top down into
place, maintaining a minimum rubber thickness.
On the other hand, if the rubber is too thick, then the mirror will be
able to flop around too much, so there is an optimum thickness, but the
optimum will be quite broad.
I don't know the properties of the 3M tape, but I would guess that it too
can handle lots of strain.
Joe Gwinn
Definitions:
Stress -- The force applied to a material. Units are pounds per square
inch or the like.
Strain -- The resulting physical distortion of the material subjected to
stress. Unitless, expressed as a fraction. For example, if the strain is
1% (0.01), the length changed by 1%.
Reversing stress -- Where the force on the material alternates between
compression and tension. If one bends a beam back and forth, the material
near the top and bottom of the beam will suffer reversing stress.
Likewise, the rubber between a glass mirror and an aluminium back as the
temperature cycles. This matters because reversing stress causes much
more material fatigue than non-reversing stress (where the sign does not
change), causing material failure that much sooner.
William H. Hathaway
something that will hold reasonably well for a week or so, then - very
important - peel off easily without a lot of cleanup. (Reuse would be
great, but I can proceed with one-use.)
However it's also got to _not_ cause/affect a static charge at the
interface. I've tried a couple of 3M stickies, as well as carpet tape,
Scotch foam double-side, and even three kinds of putty. Only one
material so far works right (one of the putties), so I'd like to find
some alternatives as backups or for better performance.
I _could_ try to ask 3M for samples of everything they've got, but
I've gotten several free samples from them so far and I don't want to
push it unless I have a good idea of what I'm asking for. If I get
something right, I'd make a decent sized paid order.
Anyone with knowledge about these tapes? Or of their competitors?
In spite of published tech data, I don't think they consider the
electric charge effect, so I really have to experiment with each.
(My project is sorta kinda optics related - I use clear PMMA that needs
to be held in place for handling and further treatment. But this doesn't
fit in the polymer newsgroup nor any of the electric-type charge groups.
So here's hoping...)
Wm. Hathaway
Joe Gwinn
<hath...@stsci.edu> wrote:
> I've been trying various double-sided tapes for another use and I need
> something that will hold reasonably well for a week or so, then - very
> important - peel off easily without a lot of cleanup. (Reuse would be
> great, but I can proceed with one-use.)
>
> However it's also got to _not_ cause/affect a static charge at the
> interface. I've tried a couple of 3M stickies, as well as carpet tape,
> Scotch foam double-side, and even three kinds of putty. Only one
> material so far works right (one of the putties), so I'd like to find
> some alternatives as backups or for better performance.
>
> I _could_ try to ask 3M for samples of everything they've got, but
> I've gotten several free samples from them so far and I don't want to
> push it unless I have a good idea of what I'm asking for. If I get
> something right, I'd make a decent sized paid order.
>
> Anyone with knowledge about these tapes? Or of their competitors?
> In spite of published tech data, I don't think they consider the
> electric charge effect, so I really have to experiment with each.
>
> (My project is sorta kinda optics related - I use clear PMMA that needs
> to be held in place for handling and further treatment. But this doesn't
> fit in the polymer newsgroup nor any of the electric-type charge groups.
> So here's hoping...)
I would guess that a suitable tape is made for use inside cleanrooms and
the like, where static electricity is a big deal.
Joe Gwinn
michael
are available--they get used in circuit board applications, and are
available from 3m among others
"William H. Hathaway" <hath...@stsci.edu> wrote in message
news:3BABE8B0...@stsci.edu...
Zane
If you go the flexible epoxy route, you can use soft brass shimstock as
spacers between the mirror and plate to get the glue pads the same
thickness. As mentioned, a number of small pads spaced around is a good
way to go.
You can practice getting the glue pads to look the way you want by using a
piece of plate glass on a metal plate similar to your mount. You can then
get a measure of exactly how much glue to put down per pad, as well as
check the strength of your bond.
Zane
P. Danek
their technical service department and tell them exactly what your
requirements are. I am sure that they can send you a sample of a
product that is close to what you are looking for. If you just want to
buy some and try it out yourself you can get them through electronics
suppliers such as Techni Tool or Contact East (www.techni-tool.com and
www.contacteast.com).
Good Luck,
P. Danek
Roland Smith
wrote:
[Snip]
>I don't know the properties of the 3M tape, but I would guess that it too
>can handle lots of strain.
I have found tape ok for really quick and dirty mounting of something
for an afternoon, but it _will_ droop and slip badly over an extended
period of time. I have found a mirror on the optical table instead of
a mount as a result of this once or twice :( .
In general I would steer clear of double sided tape and go with
silicon rubber.
All the best, Roland
P. Danek
badly I can't get them apart without damaging it or after a few weeks it
falls off on its own.
P. Danek
Bertho Boman
the 3 dots at 50% or 70% radius.
I would expect them to be place equally spaced=120 degrees apart.
What am I missing?
Bertho Boman
Bob May
placed at 120deg. to each other. The mention of 50% or 70% is two differing
theories of the best place to support a piece of material according to
either the latest analysis of the stresses on the material (50% zone) or the
traditional analysis that was done over a century ago by the intuition of
those of that time (70% zone). When you deal with basically light thin
stuff, the errors over a large surface can accluminate to the point where
the glass will be out of the constructed tolerance over a significant part
of the surface.
I might also mention that there's been intentional stressing of glass in
telescopes for several years to produce saddle shaped surfaces (several of
the Schiefspigler designs need astigmatic surfaces in order to work well) as
well as some recent work on turning spherical surfaces into approximate
parabolic surface by stressing the glass.
Then there's the work being done with active optics where a mirror is
stressed to return the light to the "correct" position after it's been
distorted by the atmosphere on it's way in.
--
Bob May
Imagine the terrorist's fun when they realize that a "nubile virgin" is a 3
month old girl!
Bertho Boman
It is so obvious except I kept thinking about smaller mirrors and
peripheral mounting.
Bertho