If I remember correctly this problem presented itself because the
necklace itself was too short and I believe we used to correct by
making it longer so that the design hung lower on the neck.
Sometimes making it longer works, and sometimes it doesn't. The
problem of flipping as follows:
Take standard chain of rectangular profile and 18 inches long. It has
right edge and left edge, both of the same length. Once such chain is
around a neck, the geometry completely changes. Instead of right and
left edges, it has inner and outer edges, and for the chain to lie
flat, these edges must be of different length.
Take 4mm width and 400mm length (approximately 18 inches). Inner edge
radius is 400 / 3.14 = 127.33mm, and radius of outer edge is computed
by adding chain width, which is equal to 131.33mm.
Calculating virtual length along the outer edge gives 131.33 * 3.14 =
Since we only have 400mm the missing 12.38 mm have to be found
somewhere. Depending on type of chain and link flexibility, a chain
could accommodate by opening spaces between links on outside. It
depends on number of links and connection type.
Given 2mm link, it takes 200 links to make 400mm chain. To
compensate difference in length between inner and outer edges, links
have to be spaced 12.38 / 200 = 0.06mm, which is reasonable. Such
chain will not flip because there is no stress created along outer
edge. However if number of links halved, the requirement become
0.12mm, which most of the chains do not have. This creates stress
along outer edge, which makes inner edge pop up (chain is trying to
equalize forces along both edges). When person bends forward,
resistance created by contact with skin is lost and chain achieves
equalization by flipping at midway points.
Increasing length of the chain may reduce link space requirement and
prevent flipping. Here is why: 400mm chain with 4mm links must have
0.12m link space not to stress. Commercial chains usually tighter
than that. Let's increase length of chain to 500mm. Inner radius
becomes 159.24mm and outer radius becomes 163.24mm. The difference
between inner and outer length will be 12.5mm. Number of links is 125
and link distances will be 12.5 / 125 = 0.1mm. So by increasing
length of the chain we reduced stress by 20%, and increased weight of
the chain is also beneficial in preventing flipping. Wether or not it
is enough will depend on weight of pendent and geometry of
attachment. To make the long story short, the stress may be present,
but it may not be enough to flip. The necklace will only flip if
forces generated by stress is enough to overcome weight of pendent
and in some cases the weight of lower half of the chain.
It should be clear from the above, that all these issues should be
dealt with in design stage, rather than in post-fabrication.