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Calculating weights of rings?


#1

Is there a formula to calculate the approximate weight of a ring
blank with a known ID, OD, width, height, metal/karat, etc.?

I am trying to make a database from a few known weights (usually
sizes 6 and 10). When I try to use excel, for example, to make a
formula, I notice that it is not a set percentage increase or
decrease. (what I did was take a size 10 and the percentage
difference of that from a size 6…then divided it by 4 to get the
average % between sizes…however when I try to go from a 6 to a 7 or
7 to an 8 for example using those #s, it doesn’t work) Also, I have
noticed, that the rounded outside rings are different than the flat
outsides, and the comfort fit are different from the flat insides,
and so on.

I know that it is very unlikely there is a definitive formula, and
since Im not a mathemitician Im not even sure how I would go about
starting this. But there has to be some sort of geometry formula with
area, cicrumference, taking volume of metal, etc into account where I
could get a close approximation.

Any help would be greatly appreciated.


#2
Is there a formula to calculate the approximate weight of a ring
blank with a known ID, OD, width, height, metal/karat, etc.?

I know of no formula, and all the variables would probably make it
unwieldy even if there was one. Basically you would be calculating
volume and then introduce mass(alloy). I have to calculate weights
all the time. Hoover and Strong’s catalog has info, in the way of
weight per inch, on a very wide range of products that you can
estimate pretty closely. You can interpolate for things not shown.


#3

check out page 130-136 of stuller’s mountings catalog. These are the
pages for comfort fit bands. They are listed by size,width and
thickness and each has the dwt as well. Could be very useful in your
calculations.

Frank Goss


#4
Is there a formula to calculate the approximate weight of a ring
blank with a known ID, OD, width, height, metal/karat, etc.? "

Calculate the volume of the metal in millimetre cube. Divide the
volume by 1000. Multiply the answer by the specific gravity of the
metal. This will give the weight of the metal in grams. To convert
the weight to dwt divide the weight in grams by 1.5555

Eg: Size 7 ring, 2mm X 2mm uniform thickness and width. Length =
(17.2+2) x 3.142857 = 60.3428544mm

Volume= 60.3428544 x 2 x 2 = 241.3714176 cubic mm

Weight of metal in grams = (241.371476 x specific gravity)/1000

Curtis


#5
Eg: Size 7 ring, 2mm X 2mm uniform thickness and width. Length =
(17.2+2) x 3.142857 = 60.3428544mm 

I have a question regarding this. two actually. What is the 17.2 + 2
x 3.142857…also I am assuming this formula only works with uniform
thicknesses and widths. any rounded ring, comfort fit or tapered
ring would not fit into this formula correct?


#6
Is there a formula to calculate the approximate weight of a ring
blank with a known ID, OD, width, height, metal/karat, etc.? " 

As Neil said, just consider it sheet metal, and there are many
charts of weights of sheet metal - Metal Techniques for Craftsmen
has one. This reminded me, though, of this web site:

http://grapevine.abe.msstate.edu/~fto/tools/vol

which has calculators for the volumes of about any shape imaginable.
I’ll just put it out there because it’s useful - not sure how many
days it would take to calculate the weight of a 3 stone ring with any
accuracy with it. [;>}

http://www.donivanandmaggiora.com


#7
Is there a formula to calculate the approximate weight of a ring
blank with a known ID, OD, width, height, metal/karat, etc.? " 

All the CAD programs can easily calculate the volume of any solid
model made with the program. Since there are lots of charts available
with the SG of karated alloys, the calculation becomes simple.

If you are talking about square or rectangular shanks of uniform and
non-tapering width and thickness, it should be pretty easy, same for
half-round shanks. Otherwise, well, you’re on your own.

But, I’m curious. If you’ve been making models for a while it’s
pretty easy to estimate finished (or pre-finished weight of most
projects, at least within a reasonable amount of error such that no
catastrophe will befall you. What is the goal or need for this,
exactly?

Wayne


#8
I have a question regarding this. two actually. What is the 17.2 +
2 = x 3.142857..also I am assuming this formula only works with
uniform thicknesses and widths. any rounded ring, comfort fit or
tapered ring would not fit into this formula correct?

17.2mm is the inside diameter of a size 7 ring. +2 is the 2mm
thickness of the metal. 3.142 is a mathmatical constant (22/7). The
circumference of every circle is 22/7 x its diameter. This part of
the formula (17.2+2) x 3.142 is to find the length of the metal.
Volume is length x wideness x thickness. The thickness (+2) is added
to the diameter to fine-tune the accuracy of the length.

Yes. This way of finding the volume will only work with uniform
thickness and width. There are other mathematical ways to find volume
of non-uniform shapes which may be too complex to explain here.
However, once the volume is known this method is fairly accurate. Say
you design a ring in CAD program like Rhino which will give you the
volume, just plug this volume in the formula and there is the weight
of your metal.

Curtis


#9
But, I'm curious. If you've been making models for a while it's
pretty easy to estimate finished (or pre-finished weight of most
projects, at least within a reasonable amount of error such that
no catastrophe will befall you. What is the goal or need for this,
exactly? 

I dont do wax models that’s the problem. We use seamless tubing.