The proper way to measure is as follows:

3 times the diameter of the ring, plus 3 times the thickness of the iron, plus 1/2 inch to each foot and allow 1/3 of the thickness for welding.

Should you make a large ring, say 3 or 5 feet in diameter, you would run short if the 1/2 inch to each foot were not added.

For example; if your wish to make a ring 5 feet in diameter of 1 inch iron you measure as follows: 3 times the diameter (5 feet) equals 15 feet; 3 times the thickness (1 inch) equals 3 inches; 1/2 inch to each foot equals 7-1/2 inches; 1/2 the thickness for weld equals 1/3 of an inch. The total length of stock required is therefore 15 feet + 3 inches + 7-1/2 inches + 1/3 inches equals 15 feet 10-5/6 inches.

James A. Klees

That there looks suspiciously like math... I'll just hammer on it until it looks right. :P

Inside diameter of ring in inches plus thickness of stock x 3.1416. Less to remember.

Or the center line of the ring X 3.14 Plus a bit for the scarfs for forge welding add a 1/16 to an 1/8 depending on the size of the stock. Often the math is a bit off because of uneven heating wind speed , the rotation of the earth or not enough caffeine. The the fact is that a hand hammer is not a precision tool you will have to adjust as needed but start with math.

Glenn, is that 3x ID or 3x OD?

As he did not say, I will guess (suggest) that it is on center line.

So I would be more inclinded to go with an avrerage- ID and OD, both x 3.14 then evarage it out. I did it with your 5' ring and came up with 15.95' or 15' 11.4"... Within an inch of your formula...

Anyone game to try it out????

Has anyone thought of using PI or is that just gona make everyone hungry?

Ian

Forget OD and ID its the center line of the ring or for that matter what ever line you are tiring to follow to figure your length on a bend.

Inside diameter of ring in inches plus thickness of stock x 3.1416. Less to remember.

Pie? I like Pie! I also like PI. But I like Pie better.

Ian, Peacock served us some PI a few reply's back. Mmmmmm it was good too. Sorry I ate it all.
Although Mr Klees method works, PI is much easier to remember.
Mark<><

I've made a number of forge welded rings to dimension, and I always used the formula in "The Blacksmith's Craft." Pi x mean diameter ("mean" indicates "average"). After multiplying, you add one times the thickness to allow for upsetting and scarf making.

To obtain the mean diameter, it is easiest to do what Peacock recommended: measure the ID and add the thickness. Another way to say it or look at it, measure the diameter from the inside to the outside. In any event, it is easier for a smith to obtain the mean diameter that way than to measure from mid line to mid line of the ring. You get the same result.

Pi can be a decimal or you can use fractions; ie., 3 1/7 or 22/7, same thing.

We are dealing with something in the metal world called, the "neutral axis." The mean diameter is neither the ID nor the OD, but the neutral axis of the stock. The same thing applies when measuring curves, say, an S shape of stock. If the S shape is full scale on your shop print or layout drawing, and you're trying to estimate the length needed, you measure the neutral axis. This can be done with a wheel traveler or a hay wire.

I had a student once who was a high falutin' mathematician from the Los Alamos, NM, Lab. When we talked about the ring formula, I called it "math." The student said, "Frank, you're not doing math; you're doing arithmetic!"

http://www.turleyforge.com Granddaddy of Blacksmith Schools

Frank,
Did you ask this student why his math did not match the reality of the testing at his work?

I have found it more difficult to shrink a ring than stretch it...make it 3.14 x the ID and cold stretch to size...you need to make it round from whatever your choice bending/welding operation is anyway. May as well be under to begin with.

Ric

when I took my journeyman test, if it didn't fit you didn't pass,...outside to inside x pi plus an inch

I'm just curious what in the heck you guys are making that requires such close tolerances. Any use I have had for a ring, it was fine for it to be a little over or a little under spec size.

Mac T, I sometimes make a band to shrink fit on a Little Giant broken clutch pully. It's gotta fit, if done right no welding ,bolts, or rivets, shrink fit makes a nice repair. I also did this on Tom Clark's first air hammer when he was researching the use of the cogged belt, it covered the v belt grooves so we would have a flat pulley.

So thats pretty good!
Out of all these post there are about 6 different ways to get to the ring size and they all do just about the same thing. I've always maintained there as many ways to do something as there are people doing it. It's what you remember or figure is the easiest way at the time. May not always be right for everyone.... but it is a way

Now, how about a bit of that PI :lol:

well you could use Schwarzkoph method and multiply by 22/7