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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 =

412.38mm.

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.

Leonid Surpin

www.studioarete.com