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Springback or Jump Ring Ahead

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Categories: Instruction and information; Jewelry

Word count/read time: 516 words; 2 minutes

Spring back is something you do. Springback happens when tension on an object is released and the object attempts to revert to its original shape. It is where the elastic deformation stops and plastic deformation begins. For jewelry (chainmaking or chainmail), it's all about how tight those jump rings are.

Wrapping wire around a mandrel will cause the wire to mimic the mandrel's profile. For basic jump rings, the dowel and wire are both round. The actual or observed inner diameter measurement compared to the mandrel diameter indicates the degree of springback. Virtually every (jewelry) metal experiences springback in this manner except maybe dead-soft fine silver or gold.

Ideally, expected and observed diameters would be identical. However, the jump ring I.D. will be larger than the mandrel. Each metal is different so to get a perfect 1/4" inner diameter jump ring might require a 0.24" mandrel for annealed sterling silver compared to 0.21" for spring temper (hardened) stainless steel.

The I.D. is the dragon to chase. Aspect ratio is based on the I.D. measurement and the wire thickness, the latter of which should be known beforehand. Sometimes an A.R. variation of 1% can make certain weaves fail! The importance of properly sized jump rings can't be understated because it ultimately affects how a weave looks and behaves.

There is no simple formula to effectively compute springback without taking measurements of the finished ring. It depends on the tension of the wire when winding, its thickness, temper, and mandrel diameter. Basically, it's trial and error. The ability to perfectly reproduce the same conditions each time so that batch X is the same as batch Y, even if made years apart, is crucial.

The most direct way to compute springback is to measure the finished I.D. of the jump ring and divide it by the actual mandrel diameter. This requires a precise vernier (down to 0.05mm if possible) and the ability to measure it properly. Easier said than done sometimes.

Lacking a good set of vernier calipers and/or mechanical aptitude, simple math will suffice. Before the tension is released from the coiled wire, count the number of coils on the mandrel down to the smallest fraction possible (i.e., "3" wraps might actually be 3.1 or 3.15 wraps). When the tension is released, count again. Divide the first number by the second and subtract one to get the springback.

Both methods give a percentage of feedback. Method one already gives the actual inner diameter since it was physically measured. For the second method, a little more third-grade math will find the (computed) I.D. increase by multiplying the mandrel diameter by the percentage. Thus, 1.5% springback on a 0.500" mandrel yields a 0.5075" I.D. ring.

Example uses 1.6mm round wire and a 1.0cm mandrel with 1% springback:
In a perfect world: 1.0cm I.D. / 0.16cm wire diameter = 6.25 AR
Actual: 1.01cm I.D. / 0.16cm wire diameter = 6.31 AR
That's enough of a difference to matter as there are additional factors that could change the A.R. including how much the wire compresses, stretches, or squashes as it's being wound.

Posted by M: March 12, 2023

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