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Interference fit for a coin bezel


#1

I’m having a two-piece bezel made, that will fit around a coin. The
pieces will be made in a base metal, which I believe is brass, and
will be silver plated.

The back half will have four (“male”) tabs that will be pressed into
four corresponding (“female”) notches on the front half. The goal is
to size these parts so that when they are pressed together, they will
achieve an interference or shrink fit, that will then hold the
assembled bezel together around the coin. I’m looking for a permanent
bond; I don’t want anyone to be able to open the bezel or remove the
coin.

I’d like to get some advice on the size of the interference. I’ve
read one posting that seems to suggest that the total interference on
notches should be .004" inches. So in this case, the tabs should be
.004" wider than the notches into which they’ll be pressed. Does this
sound correct?

Here’s a bit more detail that may be important to the answer- the
piece is about an inch in diamter, and when assembled, about 3 mm
(0.118") thick. Without any interference adjustments, the tabs and
notches are 4 mm (0.16") wide, and they prodtrude 1 mm (0.04") into
one another. The metal is .75 mm thick (0.03").

There is a concern that applying too much force to press the halves
together will damage the integrity of the piece. So I’m looking for
the minimum interference that I’d need to use, which could be pressed
together with the minimum amount of force.

One more question- all of the surfaces involved in this fit will be
siver plated. Would you expect that this will introduce any problems?
I know that the plating thickness will need to be taken into account
to achieve the desired interference. But will the plating introduce
any problems? Is it likely to rub or flake off as the two halves are
pressed together?

Thanks for your help.