Blank & bezel
The length of strip to cut for a ring or a bezel, allowing for the thickness of your stock and the metal you lose to the saw.
4.0 × 1.5 mm · Sterling silver 925
How to calculate ring blank length
A ring blank for a UK size N in 1.5 mm stock needs a strip 58.5 mm long, before the saw kerf. Add the thickness of your metal to the inside diameter of the ring, which is 17.11 mm for a UK N, then multiply by pi. The strip has to be longer than the inside circle because the outside of the bend stretches while the inside compresses, and the line that keeps its original length sits halfway through the thickness.
cut length = (inside Ø + thickness) × π
A worked example
A UK size N½ is 17.31 mm inside. In 1.5 mm stock the sum is (17.31 + 1.5) × 3.1416, which gives 59.1 mm. Cutting to the inside circumference of 54.4 mm instead would leave you nearly 5 mm short, which is the most common reason a first ring will not meet.
Blank length by ring size
| UK size | Inside Ø mm | 1.0 mm stock | 1.5 mm stock | 2.0 mm stock |
|---|---|---|---|---|
| G | 14.32 | 48.1 | 49.7 | 51.3 |
| H | 14.72 | 49.4 | 51.0 | 52.5 |
| I | 15.12 | 50.6 | 52.2 | 53.8 |
| J | 15.52 | 51.9 | 53.5 | 55.0 |
| K | 15.92 | 53.2 | 54.7 | 56.3 |
| L | 16.31 | 54.4 | 56.0 | 57.5 |
| M | 16.71 | 55.6 | 57.2 | 58.8 |
| N | 17.11 | 56.9 | 58.5 | 60.0 |
| N½ | 17.31 | 57.5 | 59.1 | 60.7 |
| O | 17.51 | 58.2 | 59.7 | 61.3 |
| P | 17.90 | 59.4 | 60.9 | 62.5 |
| Q | 18.30 | 60.6 | 62.2 | 63.8 |
| R | 18.70 | 61.9 | 63.5 | 65.0 |
| S | 19.10 | 63.1 | 64.7 | 66.3 |
| T | 19.49 | 64.4 | 65.9 | 67.5 |
| U | 19.89 | 65.6 | 67.2 | 68.8 |
| V | 20.29 | 66.9 | 68.5 | 70.0 |
| W | 20.68 | 68.1 | 69.7 | 71.3 |
| X | 21.08 | 69.4 | 70.9 | 72.5 |
| Y | 21.48 | 70.6 | 72.2 | 73.8 |
| Z | 21.88 | 71.9 | 73.5 | 75.0 |
Saw kerf
A piercing blade removes about 0.3 mm of metal as it cuts. Either cut on the waste side of your mark, or add the kerf to the length. On a thin blank this is the difference between a join that closes and one that sits open.
Bezel strip length
The same sum with the stone diameter as the inside measurement and the bezel wall as the thickness. A 5 mm stone in 0.3 mm bezel needs (5 + 0.3) × π, which is 16.7 mm of strip.
bezel length = (stone Ø + bezel thickness) × π
Keep bezel walls between 0.25 and 0.5 mm if you are pushing them over by hand. Above that you are into hammer setting or a bezel roller, which is normal on gold, but it is not a job for a pusher and thumb pressure. The height of the bezel does not affect the length, so cut that to suit the stone's girdle separately.
Wide bands
A band wider than about 6 mm grips more of the finger and wears tighter than a narrow one at the same size. Many makers cut wide bands a half size larger. This calculator gives the geometric length, so make that allowance yourself before you saw.
Common questions
Why is my ring blank longer than the ring circumference?
Because the measurement that matters runs through the middle of the metal, not around the inside face. Adding one thickness to the inside diameter before multiplying by pi accounts for the metal on the outside of the bend.
Do I add the full thickness or half?
Add the full thickness to the diameter. That is the same as adding half a thickness to the radius on each side, which puts your measurement on the neutral axis halfway through the metal.
How much longer should a thick ring blank be?
Every extra millimetre of stock thickness adds about 3.14 mm to the blank. A size N½ in 1 mm stock needs 57.5 mm, and the same size in 3 mm stock needs 63.8 mm.
How do I work out a bezel for an oval stone?
Pi times the diameter only works for round stones. For an oval, measure the perimeter with a strip of paper or thin wire around the girdle, then add one bezel thickness.
Should I allow extra for filing the join?
Cut to the calculated length and file the ends square rather than adding length. If you routinely lose metal squaring up, turn on the saw kerf allowance instead.