Wally wrote:
On Thu, 15 May 2014 17:18:17 +1000, "David Hare-Scott"
wrote:

I was working with an add-on +3 dioptre magnifying lens, the kind
that screw on like a filter, and dropped it. The lens came out of
its mount but to my surprise neither the mount nor the lens itself
were damaged.

I found the retaining spring on the floor and worked out which way
the lens went into the mount, it sits against a flange with the
retainer on top in a slot inside the rim of the mount. I then set
about replacing the retainer on top, it is roughly a circle of thin
springy metal that has been cut.

I tried putting one end in first and then working around to the
other end but each time, no matter how hard I pushed it into the
slot in the mount, when I got to the other end about 1mm was left
overlapping. I tried pushing the two ends in opposite directions so
that they would slide past each other down together into the slot.
I tried putting the two ends in first and working the curve into the
slot, hoping that it would pop inside the rim. Nothing worked.
Clearly as it came out of the slot there must be a way to get it in.
In the end I gave up and cut 1mm off the spring. The lens is now
fine.

Is there some way a normal tool-using human can get this retaining
ring in or do you require special tools?

Heheh, I've had a similar situation once. An interesting puzzle.

I think the only way to get it in without modifying it is to put the
ends in first and then force the rest of the circle into the groove. I
can't say how you do that without the retaining spring jumping out at
the last moment. It will depend on your exact situation.

Clipping a millimeter off solves the problem for now, but increases
the chance the retaining spring will come out again some time in the
future.

You could put a drop of white glue on it to make it more secure. If
you ever do need to remove it, white glue will soften in water.

W

White glue = PVA, commonly used to glue wood and paper?

D