7.0) Regluing the Magnets:
"even more mallets..."
This is the most critical section of the repair. Read this whole
section several times through before you begin. Rehearse it in
your mind until you have a feel for what you're going to be doing,
when you're going to be doing it, and how long it'll take.
Be sure to have clean, dry hands before starting this section.
7.1) Remove the magnets:
As we've already discussed, losing track of the magnet's correct
orientation on the mirror will condemn you to death by trial-and-error.
Be careful not to smudge the markings you've made on the mirror or
- If the magnets have already detached themselves from the mirror,
you're fine. If not, gently grasp the mirror (by the edges!) in your
fingers, and use tweezers or fingernails to remove the magnets.
The magnets should come off with very little effort.
7.2) Clean mirror and magnet surfaces:
- Remove the remaining bits of old glue by applying some methanol
to a cotton swab. Clean the back surface of the mirror of glue,
being careful not to get any methanol on the goop. (I don't know
if methanol attacks goop, and I'd rather not find out :)
- Similarly, clean the back surface of the magnet. You'll probably
have to hold the magnet in a pair of tweezers to do this without
smudging the marks you've made on the magnet.
- When you're done, you should have three pieces, namely two
marked magnets and a mirror. All three should be clean of the
old glue, and should still have the markings you've made.
7.3) Mix the epoxy:
- Mix a drop or two of epoxy on a piece of paper or some
other expendable surface. Only a small amount is required;
maybe enough to cover the end of a toothpick.
- Although it may be possible to get away with "crazy glue" or
other cyanoacrylate glues, I recommend the use of two-part epoxy
for a permanent fix.
7.4) Glue magnet to mirror and screw up:
Apply a thin layer of epoxy to the mirror in the location where
the magnet was once glued. If you get any epoxy on the goop that
holds the brass post to the mirror, get the mallet.
Place the mirror onto the epoxy, release your hand and watch what happens
when you plunk a magnet onto some slippery epoxy, less
than a centimetre away from a large metal post. Then watch in
horror as the magnet glides across the mirror on a layer of epoxy and
sticks itself to the post, smearing epoxy all over the flexible goop.
There's no recovery from this mistake; pick up the mallet and
- The first time I did this hack, I made this mistake, but managed
to catch the magnet within a millimetre of disaster. I consider myself
very lucky to have caught it in time; from the time I let go
of the magnet to the time I caught the magnet was probably less than
a second - just enough time to realize what was happening and catch it.
- OK, so you can't plunk the magnet down and walk away, for the
reason we've just discussed. And you can't clamp the magnet in place
using conventional means, because you'll scratch the surface-silvering
on the mirror.
- So you've gotta sit there, holding the mirror and magnet
(by the edges, of course) in place until the epoxy has set. With the
metal post (i.e. and resulting attractive force on the magnet) present,
that means holding it there for at least twice as long as the
instructions on the package of the epoxy. If you're using 5-minute
epoxy, hold it in place for 10 minutes. To be on the safe side, I
recommend holding it in place for at least 15 minutes.
7.5) Glue magnet to mirror the right way:
As before, apply a thin layer of epoxy to the mirror in the
location where the magnet was once glued. The epoxy should cover
the relevant area in a thin layer, with no gaps or bubbles, and
of course, be sure not to get any epoxy anywhere near the goop
that holds the brass post to the mirror.
- Check the alignment marks you made on the magnet with those
you made on the mirror. Once lined up, you should be able to
hold the mirror by the edges in one pair of fingers, and the
magnet by its ends in another pair of fingers.
- Carefully place the magnet onto the epoxy-coated
area of mirror. The sides of the magnet should be flush with
the edges of the mirror. If they're not, shift your fingers
around a little bit until the magnet is lined up correctly.
- Hold the magnet and mirror in place for at least 15 minutes.
Do not move your fingers for any reason during this time; the
less movement, the better the bond will be.
When the time has elapsed and you release the magnet and mirror,
let go very gently, and be very sure that the
magnet isn't going to move anywhere before starting work
on the next one.
- After letting go of the magnet, I usually place the mirror
face-down (on a soft surface, of course, or I'll still need the
mallet!) and just watch it for another 15 minutes. In
addition to giving the epoxy longer to set, it also gives my hand
a much-needed rest.
- All this time spent waiting for the epoxy to cure means that
by the time you're done, your first drop of epoxy will have set.
You'll have to mix another drop before doing the next magnet.
- You'll be spending at least half an hour on each magnet.
That's an hour for each mirror, or two hours for the whole set.
Plan your time accordingly.
- If your fingers are getting cramped and tired, stop and do
the next magnet another day.
7.6) Let stand overnight:
- When you're finished the last magnet, place the newly-epoxied
mirror/magnet assemblies somewhere they won't be disturbed, cover
them to protect them from dust, and leave them there overnight for
the epoxy to finish curing.
- The overnight wait is why I recommend taking detailed notes
on everything you've done to this point, particularly the number
of turns and final positions of the calibration screws. There are
enough details that you're virtually guaranteed to forget something