When the rim has been swept back over its form it will become necessary to cut off the extreme edge with a V metal tool.

This is because the material will not expand, contract nor thicken uniformly, since all sheet metal is produced by rolling. It will, therefore, extend under spinning and annealing less in a direction parallel with the original rollers than at right angles to them.

Presuming that the metal has laid itself nicely on to its form and the parallel edge has to be curled right back to form a substantial smooth rim, this is where the rim header comes in, also where the burnishers must be used. The rim of every piece becomes extremely stubborn on account of the tension in that part, and it would cut a wooden stick to pieces. It is well that it is so, for this gives great strength to the shell where it is required. In some cases one may have to fix the shell the other way round on its form so that it projects toward the tailstock. The spinning rest is mounted on the mandrel to the left, and the rim header to the right.

The rim header carries a steel ball of different size at each end. These ball ends are halved in order to allow them to be withdrawn. The end of this rod half ball outwards is now introduced inside the shell where it has been spun over, and with any one of the burnishers the metal is spun around the ball. It is supposed that the curled-over rim after withdrawal of the half ball will be left hollow. If this rim is required to be exceptionally strong, one has only to insert a ring of wire and then to spin the shell completely round this ring.

The only other two accessories are the spinning centre and the lever tailstock. These come particularly into use in spinnings which have no centre hole and cannot in consequence be fixed to the form by stud nut and washer. The discs must be held against the face of the form by a piece called a follower, usually of wood. The tailstock side of this follower is recessed to slip over the spinning centre. As the follower has to rotate freely with the form, so the spinning centre is really only a ball-bearing mounted on a screwed shank which screws into the tailstock spindle in place of its ordinary centre.

Followers are quite simple pieces, though they vary in length, diameter and shape, so these should always be put away with the form corresponding.

Considerable pressure is required, especially in the first spinning and with a small follower, in order to hold the disc and drive it round against the brake power of the spinning stick. This is the reason why the lever tailstock is so essential for this work. It is almost identical with the ordinary tail-stock, except that its spindle is much shorter and is actuated by a vertical lever. Since this accessory is also used in metal turning or drilling it is provided with a hardened centre and an adjustable ring behind the casting, which serves the purpose of a depth stop.

So far we have reached what may be termed the simple elements of spinning, which should suffice in such a treatise as this, since one can make an immense assortment of useful and saleable articles as it is, if the instructions are carefully studied. All these pieces, however, withdraw easily from forms and followers. In more advanced spinning this is not so ; in any profile bellied out, approaching a ball, a vase with a narrower neck than its body and so forth. It is obvious that the form cannot be withdrawn from the shell during the operations of spinning and annealing. So these forms are made sectional and collapsible. Usually the centre or core of the form is a tapered piece around which the profile is built up in sections suitably keyed or registered at their ends. By this means one can withdraw the taper core and the sections will come out through the narrower opening of the shell. In turning the form the sections will be glued together, a piece of paper between each, so that when the taper hole for the centre core has been bored out and the registers fitted one can easily separate the sections.

Again, the rim header, as sold, is supplied with a double-ended rod carrying half balls of different sizes at each end. This is a silver steel rod fin. diameter, 4in. long. It is in reality only a fixed support for one surface of the spinning shell while the burnisher is shaping on the other.

As one progresses one will find the necessity of such a fixed support in a number of operations, and one will make rods with all sorts of ends, grooves, ridges, rollers and so on. Some may be required to project inside the shell, others outside.

There is still another proceeding for producing profiles on shells called by various names in different trades. It consists in rolling the profile into shells or rings. A short description of this as applying to the mandrel would seem in place here before we leave the subject of spinning. Suppose one turns a profile into a mandrel screwed into the headstock, and one makes a roller with the opposite profile to rotate freely on a pin held in the tailstock. If the latter is brought up parallel with the profile in the former, then the swing of the tailstock will bring the one profile into the other. If one now places a ring or shell on the headstock profile between the two, and forces in the tailstock while the headstock is being rotated, that profile or shape will be rolled into the ring or shell. Since the headstock profiled mandrel will be so much smaller than the finished piece the latter can be easily withdrawn.