```
Maybe I'm missing something and am way off base but here goes....
```

Afraid you did, Karla. The question is what size of sheet metal

(usually a disk) is required to make a bowl or cup of a desired

final size. The answer is not much related to the volume the bowl

will hold, which is what your jet sett tries to solve for. While it

would work to find what other shape of vessel might have the same

holding capacity as the one you’ve molded, it doesn’t give you the

required surface area of the beginning stock you need to start with

to raise the bowl.

Actual calculations of that can get tricky, since in raising, or

metal spinning, the surface area of the sheet can change, variably,

depending on the technique used. The hammering can either stretch the

sheet thinner, or actually cause it to compress on itself, getting

thicker, so a given starting size of disk can actually result in

somewhat of a range of finished vessels, depending on the technique

of the person doing it.

But as Charles already pointed out, the traditional way to estimate

it is simply to take desired maximum height of the vessel and the

desired maximum diameter, and add them together.

Sophie, by the way, wondered whether it shouldn’t be twice the

height plus the diameter. That would be correct for, say, building a

box by scoring and folding sheet metal. But raising simultaneously

stretches and compresses metal. The compression of the outer edge to

a smaller diameter, while stretching it radially at the same time to

keep the same thickness, accounts for why you only add the height

once. You can adjust that starting measurement for differences in

the way you work. For example, you may wish to emphasize the

thickening of the sheet around the edge, so then you might allow

yourself some extra metal. Or if, like me, you are sometimes not as

skilled or careful as you’d like (I do raising only occasionally,

with predictable errors as a result…), and have to deal with

occasional edge cracks or excessive waviness, well, then having a

bit of extra metal you can trim off is useful. But extra metal is

also extra work. It won’t be there to trim off until you’ve gone to

the work of raising it all the way up there in the first place…

Peter