Pumpkin Pie.

[Dennis]

For those of you who are at ease with the relationship of pi to the radius of a circle, or sphere, please don’t read on; you’ll only get cross.

For those who were away when it was discussed at school, or simply turned off by it, imagine a pumpkin, round as round. Now, if you know how fat it is at its fattest point, that is the diameter, often simply called d, to save breath.

If you are a jeweller, then sometime you will want to make a ring to fit this round thing snugly. How long a piece of metal will you need? Well if you measure all the way round, you are measuring the perimeter; let’s call it l for short. That’s meant to be an l as in length.

But if you know the value of d already, you don’t need to measure l at all. You can work it out on your calculator. No matter how big or small the diameter d, if you multiply it by 3.14, you will get the perimeter l, or the length of metal to make a ring.

The number used is a constant, either written as a fraction, twenty-two divided by seven, or as the Greek letter pi, like this: π. What is more you don’t have to remember the number, because Sharp make a cheap school calculator (EL-S50) with a π key. They are only about a fiver online.

So when you see a diagram with lots of letters and arrows, it is just waiting to have the real figures put in. But if you see a letter, for example d, multiplied by pi, or just written πd, then that will give you the length of a bezel for your stone, or the length of metal for a ring.

Now comes a slight difficulty, but don’t give up. Rings have a thickness and the thicker they are, the more it affects the outcome. So to get things right, you can add twice the thickness of metal to your result.

Finger rings are a special case, because the way they feel on the finger is also affected by how wide they are. Not to worry, this online calculator will take care of it.

Use upper case for English sizes: http://mordent.com/toolsapps/
Our Wallace has painstakingly written down all the results as a table, but I’m not sure how to access it. Perhaps someone can post that link here too. Dennis.

[medusa]

yeah, but what always gets me is the… aspect ratio? If the circumference is say 10cm then what length do you cut if the wire is say 2mm thick or 4mm thick? That's what always bugs me and I can never work out.

[CJ57]

In the first ever book I bought written by a couple of girls that were at ECA just after me it said

Measure the diameter from your chosen ring size on the gauge with a ruler
Multiply by pi and add twice the thickness of the metal. This will give you the exact length of wire or metal to cut

It seemed the easiest way for me once I'd remembered what pi was !

[caroleallen]

Switched off, sorry! I like Wallace's chart - tells me everything I need to know.

[mizgeorge]

Wallace's lovely chart is in this thread: http://www.cooksongold.com/forum/showthread.php?t=5031

[lorraineflee]

Thought someone might be interested in one of the puzzles I did for my grandson when he was 8 and wanting to learn more maths. I made a booklet of Starwars maths problems up on a week by week basis. This one was on circles!
circle question.pdf

[Wallace]

awww, thank you. Love you peeps!

so it is all in one place here you go. (as a reminder the thickness is across the top and ring size down the side).

Attachment 5652

my original is in an excel spread sheet, which I can also share if anyone wants to PM their email

[Anna Wales]

Used Wallace's chart today to make 2 rings and worked perfectly. The chart has a permanent place on the bench now.

[medusa]

how could I get Wallace's chart to work for say bangles and collars? or should I use Caroline's suggestion of circumference + 2x metal thickness?

[Dennis]

For say bangles and collars should I use Caroline's suggestion of circumference + 2x metal thickness?

Please forgive the misquote, Liz.

That's the one to use I'm sure and your wearers will be quite happy.