Calculating jumprings springback

Jewelry Discussion
1

Hello, I have a question. Does anyone know of a formula to calculate
the amount of springback when making silver jumprings? I have a
commission to make a particularly fiddly chainmaille bracelet in
sterling, and the rings have to fit just right. Any suggestions will
be welcome.

Thank you. Sheri

2

I guess I don’t understand the question. But then I don’t do any
maille. I have seen many magazines at craft stores dedicated
exclusively to maille. Perhaps the answer is there.

Don Meixner

3

In general spring back depends on the diameter of the mandrel, the
hardness of the wire, how much the wire was handled before winding
the coils, etc. I doubt if there is any practical way to calculate it
without just winding the coil, cutting the rings, and measuring it.

Cheers.
John Fetvedt
bijoux-de-terre.com

4

Sorry Don, When you cut a coil to make jump rings the metal springs
back from the mandrel. Different metals have different amounts they
spring back.

I was wondering if there was a way to calculate that amount. Does
that help? Thanks for replying. Sheri

5

If you start with dead soft wire the amount of spring back in the
coil will be minimal. If you want absolutely to insure no opening of
the diameter once wound, anneal the coil while still tight on the
mandrel.

Elliot Nesterman

6

I gather you know enough about chainmail to appreciate the concept
of aspect ratios? If not, check out this article on MAIL (a huge
chainmail forum/community/database):

After a very, very quick search I didn’t find a result that detailed
specifics on actually calculating the springback, since it really
depends on several factors (the specific temper of the wire, size of
wire, size of mandrel, and the material’s inherent properties).
Another option, depending on just HOW specific of you
need and how uncommon of a ring size, would be to just look at some
ring sizes around your requirements and see what the actual inner
diameter is relative to the ideal (mandrel) ID.

My favourite source for chainmail stuff is:
http://www.ganoksin.com/gnkurl/1vc If you navigate to the material
you need they list the actual ID and mandrel ID of all their rings.
Heck, you could even buy your rings there and save yourself a whack
of time making your own. (No affiliation anymore, but I worked there
about a decade ago.)

Regards,
Mark

7 
Sorry Don, When you cut a coil to make jump rings the metal
springs back from the mandrel. Different metals have different
amounts they spring back.

Yes, but if the coil is still tight on the mandrel and stays on the
mandrel while you cut the coil, then the springback doesn’t change
the length of wire in each ring. It causes a larger gap between the
ends, which you can close again when you install the ring. If your
system means removing the coil from the mandrel in order to cut it,
then one way to keep it from springing back is to anneal the coil
while still on the mandrel. If the mandrel is stainless steel, then
the whole thing can go in the pickle, mandrel and coil and all,
which removes any firecoat like Prips flux or borax, or whatever,
both from wire and mandrel, so then the coil can be removed easily
from the mandrel. The downside to this, of course, is that you may
not want dead soft rings…

Peter

8 
Does anyone know of a formula to calculate the amount of
springback when making silver jump rings?

That will depend so much upon the exact hardness of the wire that I
think you must experiment to find the right mandrel for an exact fit
for your project. Then you must use the same type of wire for uniform
results, of course.

  • M’lou
9

Hi Sheri,

I also am not sure exactly why you want to calculate the amount of
springback in the rings. Is it because you want to get all the rings
precisely the same diameter? this will happen already as long as the
rings are evenly wound onto the mandrel and the rings are cut with a
fine blade.

when you close (bend) the ring and make it flush, it will close the
gap created by both the spring back and the saw cut. In terms of the
final inner diameter, because you are bending the ring to close the
gap, it will 1) reverse any spring back and 2) account for the saw
cut. In effect the only factor you need to worry about is the width
of the saw cut on the inner circumference.

(presuming you are not intending to join the links…)

In terms of materials engineering maths, continuum mechanics (the
maths describing how to calculate final shape after deformation) was
the single hardest subject I ever attempted.

You need to know the yield point, modulus and deformation hardening
rate (which depends on composition microstructure and heat treatment)
for even a linear approximation.

if you don’t need micron accuracy, you can do better, but only if
you know the yield point. Ignoring hardening, the amount of spring
back is determined from just the modulus and the yield point.

e.g.

http://www.ganoksin.com/gnkurl/ep81s6

modulus = stress/strain
spring back strain = yield stress/youngs modulus

for “silver” from the previous link, Youngs Modulus for silver = 71
GPa - this will stay almost constant for alloys that are mostly
silver, regardless of heat treatment

Yeild Stress = 54 MPa for Silver, 126 for sterling silver, 136 for
ASA: this is the factor that changes with composition and heat
treatment/microstructure

lets go with sterling:

strain = 126/71,000 = 1.77 x 10^-3

so for a linear length of sterling silver wire 1 m long, stretched
past it’s yield point, when it is cut it will spring back 1.77mm.

10

If you wrap the rings in tape, prior to cutting, you won’t have
springback.

I find that rings wound on metal mandrels are less likely to spring
back.

Judy Hoch

11

I’d use a disposable wooden mandrel with holes at each end. Fix the
wire to one end, wrap it and then fix at the other. Then wrap with
tape.