This section is from the book "Spons' Mechanics' Own Book: A Manual For Handicraftsmen And Amateurs", by Edward Spon. Also available from Amazon: Spons' Mechanics' Own Book.
Cups differ from cylinders in the addition of a bottom and the necessity for strengthening the upper edge or rim. The sheet is set out as already described to form the upright or sloping sides, with allowance for a lapped joint, and a disc is cut out for the bottom about 1/8 in. too large all round. Before converting the sheet into a cylinder or frustrum of a cone, the margins must be prepared. The upper margin is provided with a rim by turning down about 1/8 in. of the edge, by the aid of a mallet and hatchet stake, in such a manner that the actual edge of the metal shall lie quite close against the outside surface of the article, while the rim retains a fullness and rotundity. If the article is of a size to require this rim to possess considerable strength or rigidity, this feature is gained by enclosing a piece of wire, of suitable gauge, within the rim. Care is needed to make the turnover of the same width exactly all round, otherwise the rim will present an uneven surface. Wiring facilitates the operation of making a rim, but has sometimes to be dispensed with, as, for instance, when a cover is to fit tightly over - in canisters for storing goods, for example.
The next step is to prepare the lower margin for receiving the bottom, which may be done either before or after the sheet (with its rim formed and wired) is bent to a cylindrical form. In the former case, the margin is held on the hatchet stake, and about 1/8 in. is hammered out at right angles all round, so as to form a flange or foot to the cylinder; in the latter case, the perfected cylinder is slipped over a round bar held in a vice, and supported with the lower margin resting on the bar, so that blows with a hammer on the outside will turn the margin slightly outwards, when, the bend being thus commenced, the cylinder is stood on end, and the hammering gradually proceeded with till a right angle is attained. The foot of the cylinder may either be turned over the disc forming the bottom, or it may have the disc turned over it instead, the latter being the easier method. To make a folded seam, with the bottom turned up over the foot, stand the cylinder centrally on the disc, and mark the margin extending beyond it. Then remove the cylinder and proceed to turn up a flange on the disc by holding it on a flat circular surface as near the right size as possible, and gradually hammering it down.
When many articles of the same size are to be made, a hard cylindrical block of the correct dimensions is very useful. After the disc has bad its margin turned up saucer-wise, the cylinder is replaced in it, and the margin of the disc is closely hammered down upon the foot of the cylinder; solder run along the seam completes the joint. This folded joint is unsurpassed for strength, but it demands more metal and more time for its production, and hence is generally replaced by the following modification. The completed cylinder, without any foot or flange at the bottom margin, is stood on the disc, which has already been converted into a saucer, and the edge of this saucer is soldered to the upright wall of the cylinder all round.