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Calculating length of metal for bangles


#1

Hello Brains Trust

My head is spinning with trying to work out the correct length of
silver to order to make bangles. If you can help, I’d be so
grateful. The metal will eventually be 5mm thick (6mm high), and the
size will be medium, ie inner circumference will be 20 cms. I will
need to order the metal as 6mm x 6mm square.

I guess my starting point is to work out how long the metal needs to
be when it is 5mm thick, which will make it 83.3% of what I need to
order of the 6mms thick metal.

I’ve looked through books I have (including Oppi Untracht!) and done
a Google search and still can’t get to a formula to tell me what I
need to order of the 6mm to take account of the metal thickness, so
any help you can give me would be much appreciated. Wish I’d paid
more attention in Algebra at school!

Best wishes,
Anna Williams


#2

The same math applies to rings as bangles. Go to the Rio Grande,
Hoover and Strong or other suppliers sites and they will give you
advice in ordering the correct length of material for a ring based on
the thickness of the material. You are basically taking the inside
circumference of the circle and adding 3.14 X the thickness of the
material to that length to account for the compression that occurs
when you form the material and solder it.

We make cuff bracelets and the same math applies to cuffs. Over the
years, we have figured out a sizing system based on the length of the
material before it is bent. We do have to compensate for thicker
material and sometimes wider material than average. As a suggestion,
go to the hardware store and buy some copper wire. You will need at
least 4 gauge to equal your 6MM stock. Work with the copper until you
get the size that you want.

Lay it out flat again, measure it, add a bit and that should give
some idea how much to buy. 6X6 in silver will be expensive, in gold,
even more. Good luck. Rob


#3

Hello Anna, The formula is the same for a ring. bracelet, or bezel:
the diameter plus the thickness times pi.(20 +6x 3.14=81.64mm) If
you are cutting a length of metal to curve around a mandrel, you
should cut it a bit short (for a bracelet, about 3mm) because it
will stretch when you hammer it to shape. Have fun. Tom


#4

Are you talking about a closed bangle or one with a gap in it. H


#5

I find that formulas and math is not my best bet in these
circumstances. I approximate the length in one of two ways:

1: make a copper model in the dimensions required and then cut it
and stretch it out. This will be your blank.

2: make an analog in aluminum foil. Roll up a “snake” until it
approximates your dimensions. Form it and then stretch ou.

Take care,
Andy


#6

I might suggest buying two wrist mandrels. Use paper to wrap around
the mandrel and use for guide. there are round and oval mandrels for
this.

Otherwise here is a google shot:

Enter the width of the longest long axis, AB, and the length of the
longest short axis, CD. Then, click on Calculate. The
circumference is in whatever designation of units you have used for
the entries. The formula is PI * SquareRoot of 2 * ((1/2 long
axis)squared + (1/2 short axis)squared).

http://www.ganoksin.com/gnkurl/1mo


#7

Anna, You seem to be asking a question about how much length will be
gained when you roll out the 6mm x 6mm piece of silver to be a 5mm x
6mm piece. Is that correct?

If so, my suggestion is to ignore the amount of lengthening and just
order 8 inches. For a bangle with a 20 cm inner circumference, add
the width of the wire (5mm) and you have 205mm or 8.07 inches. When
you have rolled out the wire, you will have a little more than that
for cutting and filing the ends and a tiny amount–maybe a couple of
mm-- left over.

Anyway, I don’t believe you can order wire in less than 1 inch
increments.

Hope this helps. vera


#8

Hi Anna,

Since you intend to start with 6x6mm square wire to make 6x5mm wire
to make a bangle with inner circumference of 20cm you will need to do
2 calculations.

The first is to calculate the length of 6X5mm wire needed to make
the bangle. This is easy. Its simply 200 + 5x Pi = 200 + 15.7 =
215.7mm. (See below for the reason).

The second is due to the fact that when you roll the square wire
down to 5mm thick, it will get both longer and wider. I’ve created a
calculator at http://www.ganoksin.com/gnkurl/ep8267 which will do
this for you.

Using the calculator, enter the required width, thickness, and
length of wire required:

That’s 6, 5, and 215.7 The calculator tells you that you should start
with 203mm of 5.6mm square wire, which can be made by rolling 180mm
of 6x6mm wire down to 5.6mm square.

So the process is:

  1. Roll 180mm of 6mm square wire down to 5.6mm square. This gives
    you 203mm of 5.6mm square.

  2. Roll the 203mm of 5.6 square down to 5mm thick to end up with
    215.7mm of 6x5mm wire.

  3. Bend this into a ring and solder it up.

Here’s the reason for the 1st calculation.

Imagine the stock that you want to bend into a circle to make a ring
is made of lots of very thin layers. When you bend it, the outside
layer is stretched and the inside layer is compressed. The layers
next to these extremes have to stretch or compress a little less, and
so on until you get to a layer near the middle that remains the same
length.

This layer is called the neutral layer.

It is convenient to assume that the neutral layer is in the middle.

To determine the length of stock needed, you simply have to
calculate the length of the neutral layer. This is equal to the
diameter of the neutral layer x Pi. The diameter of the neutral layer
is the inside diameter (call it ID) of the ring plus the thickness of
the stock (there is half the stock thickness on each end of the
inside diameter).

Therefore, the length of stock is…

(ID + stock_ thickness) x Pi. or ID x Pi + stock_ thickness x Pi
Because the inside_circumference = ID x Pi. The length of the
neutral layer is inside_circumference + stock_thickness x Pi.

I hope this makes sense.


#9

I don’t make bangles. I have serious safety concerns with bangles but
I did once consider them as a product for my shop and I had the same
question. My father offered this suggestion.

Go to the hardware and buy 10’ of 10/2 wire with a ground. Twist it,
hammer it, work it however you like. Cut it, solder it, measure as
you go and take notes.

Dad was all about the simplest most direct method. Once I knew how
long a piece of stock was needed for a given bracelet I cut 1/2"
CPVC tubes to that length and capped on end. I have a set of stock
length gauges that I use daily as a result.

The waste in material is not an issue as there is none.

Have fun.
Don Meixner


#10

Di Don

 I don't make bangles. I have serious safety concerns with bangles
but I did once consider them as a product for my shop and I had the
same question. My father offered this suggestion. 

your 1st paragraph comments that youve had serious concerns in the
past, about making bangles. Now ive made several 1000’s of them and
have never had a return on safety grounds. Which type of bangle is it
you have concerns with?. I see bangles being in 3 basic designs.

  1. as a complete circle
  2. as a cuff type that oval that open
  3. various shapes in a circle but are hinged and catched to put on
    and off.

Await your thoughts, as there can be concerns with necklaces in
heavy chain to get caught in things and rings subject to catching on
hooks etc. nothing is ever perfectly safe worn on or through the
body. Have you any case stories to relate?

Ted


#11

This info is available from many different sources as graphics and
links to pages on Pinterest. Don’t forget Pintetest as a place to
search for info about metalsmithing!!!


#12

Hi Ed

I work in the field of handicapped access and I design and build
special needs equipment. Thirty years ago one of the therapists I
worked with caught a bangle bracelet on a screen door latch, slipped
and snapped her wrist. In that time I have made a great many cuffs
and quite a few heavy chain bracelets. On the cuffs I have no
worries. On the chains or linked chain bracelets I have always left a
few jump rings unsoldered so I am not concerned about them either.
But the concern over that one broken wrist has bothered me for years.

By the way if a customer buys a ring from me at a show and then
slips it on their thumb they get The Thumb Ring Lecture as well.

Perhaps I worry unnecessarily but that’s a decision I have made.
Some one else can have the bangle business. I am doing fine with
cuffs.

Thanks for wondering.
Don Meixner


#13

Hi again Ted,

I thought I owed you more explanation about my bangles comment.

Jewelry safety is a big issue with me. Both in the wearing of it and
in the making of it. The worse burns I have ever had were caused by
hot polish from a wheel. And an emergency room Doc told that had I
been wearing my wedding ring I’d surely have lost fingers from an
industrial accident.

Do you remember the great gloves while polishing debate of about a
year ago? I think we need more interchanges like that. Shop safety
is more than a neat shop which mine isn’t. It is how we handle the
material we work with and the tools we use. It is as much mental as
it is environmental.

I had to cut a toe ring off a young girls foot because it has been
stepped on and she hasn’t bought a split ring. They have their own
dangers by the way.

I’ve seen fingers skinned by poorly fit and finished rings. Usually
because people wear jewelry while they work when they shouldn’t. But
an injury just the same that could have been avoided with more care
taken by the Jeweler and the wearer. I know of a nipple ring that
was torn out because a stage hand wasn’t paying attention to what he
was doing.

I think by now we all know not to machine polish chains but that’s
us. It isn’t the new hobbyist that bought equipment before they knew
how to safely use it.

I see art jewelry in magazines that looks like it was fun to make
but would be a danger to wear. And if it is dangerous to wear it
would be dangerous to machine polish. And you can say that any real
goldsmith would know better and hand finish such a piece but I keep
thinking back to that hobbyist who doesn’t know better yet. It would
be a hard lesson to learn.

I really appreciate you asking me about this. I don’t want any one
to think I am some snarky jackass or Puritan wowser on a tear. For
me it is simple. I worry about safety. I don’t make bangles and you
get the thumb ring lecture. :slight_smile:

Don Meixner


#14

Don brings up a good point about safety. I learned a difficult
lessonjust a few weeks ago. I was drilling a tiny piece of copper
for a demo I will be giving in riveting, and the piece was too small
for me to clamp down or get a good grip on, so it spun around on
thedrill bit, slicing into my finger. Blood spurting out of the
wound. Learned my lesson. Drill hole into a large piece, then,
measuring carefully cut out the small circle, or square around the
drilled hole. Alma


#15

Don-

I always appreciate your jewelry wisdom. Regarding bangles, I have
small hands and wrists (the only petite parts of me). Cuffs, no
matter how beautifully fabricated and gorgeous looking, generally
turn around on my wrists and then crash to the ground (often it’s an
asphalt parking lot as I’m leaving a store).

My drool-inducing collection of cuffs is impressive but I no longer
have the pleasure of wearing them. That moment when they hit the
ground is heart-stopping.

It’s been suggested that I wear an adhesive-type moleskin on my
wrists to hold the cuffs in place. Creepy idea.


#16

i use fine silver for cuffs it bends easy and fits my small wrist


#17

Hi Marly,

In our two shops my brother Rob and I build lots off jewelry besides
cuff bracelets. But cuffs are what our father became known for and
we have continued his legacy both in our own very distinct designs
as well as the legacy designs that Dad left us.

One of the things Dad developed was a method of sizing and shaping
cuffs that helped create very good fits. We each have our own twists
on fitting to some extent but the end result is the same. When you
leave Rob’s shop or a craft show that I am doing your bracelet fits.
I have gone as far as having a customer wear a bracelet around the
show for a while. That way they know for sure of the fit. I have
never lost a bracelet and I almost always make the sale.

If you have to squeeze the bracelet a little tighter then it’s too
big. You should buy a smaller size. I am very aware that that isn’t
always possible with casual and costume jewelry. But if you are
having a piece made the fit should be right for you.

I have never heard of using a piece of moleskin on the inside of a
bracelet to improve the fit before. Do you know if it works?

Regards your legion of cuff bracelets. Have you asked if a craft
Jeweler in your area could cut them down and reshape them to fit
you? Sometimes it takes as little as removing a quarter of an inch
of metal or a simple reshape.

Regards
Don Meixner


#18

Don Meixner-Thank you so much for your generous and informative
response.

As a silversmith, I am wary about working with base plated metals
(costume jewelry). I love wearing the huge bold designs which is why
I have file drawers filled with truly fabulous jeweled cuffs.

The moleskin is first affixed to one’s wrist & then turned so that
the sticky part sticks to the cuff. Not for me. I’ve thought about
soldering (or perhaps using hypo-cement) and putting a jump ring on
each cuff end and then a little chain with a spring-ring clasp.

To my surprise, I’m going to be 83 on May 2. Blessed with lifelong
ADHD (yes, I am being sarcastic), I am still hyper and annoyingly
energetic but modifying costume jewelry does not feed my soul.


#19
i use fine silver for cuffs it bends easy and fits my small wrist 

it does bend easily. But it also never gets really hard and springy
enough to reliably hold that shape. Bends easily yes, but bends out
of shape just as easily. Be careful using it for customers who might
be dismayed at how easily their bracelet gets all dinged and bent out
of shape…


#20

Been there. Done that. I’m one of those hobbyists who doesn’t have machine shop experience. I have a book “The Jewelry Workshop Safety Report”–I recommend it. I’ve learned to think “what could happen if…” and I don’t use power equipment by default–sometimes I just make my mistakes faster with it :smile: Here’s hoping all my injuries and yours are minor!