Metal shells, after being cupped, drawn, or raised, have sometimes to be expanded, necked, bulged, or otherwise altered in shape. In some instances this is done by means of special expanding dies, and closing, necking, or reducing dies; but usually the operations of bulging or necking are performed in the spinning lathe. The lathe consists of a bed fitted with a fixed headstock, which carries the chucking mechanism for receiving such articles as are seen at A, B, C and D, fig. 112. These represent common examples of spinning. They are held in position by a moveable tail stock. The spinning operation is usually performed by special burnishing or friction rollers, these being carried upon a compound slide rest. The pressure of these rollers or burnishers against the article forces the metal to flow into the desired shape, the outline being governed according to the point at which the pressure of the rollers is brought upon the article. The examples E, E I, F, F I, fig. 112, are of cornish-pole end stampings, the small amount of spinning required on these being to connect the two halves together. This would be done by fixing one half of E or F in the chuck, and expanding a little at 0 or L by means of a hand-spinning tool. Then E 1 or F 1 is taken up by the hand to insert P into 0, or M into L, after which O or M is rolled or spun over P or L, as the case may be, by exerting a slight pressure upon the metal by means of the hand-spinning tool. The various stages of this method of spinning are shown at

Fig. 112.

Fig 113.

A, B, C, fig. 113. The first shows E and F alike. In the second stage E is seen to have been expanded, whilst F has been inserted into E, and in the third stage E has been rolled or spun over F. Another example of joint spinning, where the metal is turned down at a sharp angle, is seen at fig. 114. A copper float ball for a water cistern and tank work forms a good illustration of jointing (see fig. 115), where A and B are portions of hemispheres which are jointed together to form the sphere. Hemispheres A and B are both drawn or raised in the same die, afterwards the edge of one is trimmed off in a slitting shear machine, and when Aand B are joined together the broad edge E overlaps the smaller edge F. This rolling or spinning joint metal work is done in many different styles, and by the assistance of quite a variety of special tools, but figs. 113, 114, and 115 will serve to illustrate the principle upon which the spinning is carried out.

Fig. 114.

Fig. 115.

Much of the ornamental work, such as bedstead knobs and similar mounts, used for central and end embellishments, are changed in form after they have left the drawing press, by means of a simple high-speed lathe containing a former in the end of its spindle (see fig. 116), where the arrangement is that a spindle S carries a former, which goes inside the work to be shaped. The metal cup C has been drawn in a press, and is about to be shaped to the former F, which is made sufficiently small in diameter for the purpose. Its largest diameter must, never exceed the smallest diameter in the work to be shaped, or the articles shaped thereon could not be drawn off when finished. A simple roller R is used, mounted between the forks at the end of a suitable lever. This lever will be seen at fig. 117, and it would be worked preferably by the foot. The contour of the roller corresponds with the shape of the exterior of the finished article, only it may be much larger in diameter.

Fig. 116.

Fig. 117.

The partly-formed article is slipped on to the former, and held against it, whilst the pressing on the end of the lever at E causes the external roller R to force the sheet brass to the form of the central mandril, or former F. This causes the work to rotate, and by this means swells and indents can be rapidly formed on any raised or drawn article, and the cost of labour is very trifling. Not only can plain swells and indents be formed, but ornamental work can be done, such as milled edges, either straight, crescent shaped, spiral, or in the form of beads; in fact, this arrangement enables many designs to be produced that cannot be done by any other way but casting, and it has the great advantage of cheapness as regards the tools, another advantage being that skilled labour is not required to work the tools. Referring again to fig. 116, when the article C has been shaped by the action of the rolling, the finished diameter of the cup must be sufficiently large to enable it to be readily removed from the former. In other words, the diameter of the part of the cup C, made by A on the roller R, must be large enough when finished to pass over the diameter of part B on the former F. This will be done by commencing with the proper sized cup, according to the shape of the article, and the amount of rolling required.

The operation of spinning the end of a wire rivet so as to form a head is a novel example of the useful application of spinning rollers. Fig. 118 is one of two chucks that would be employed in spinning both heads H, H1 of the rivet A.

Fig. 118.

The chuck at K is screwed into the spindle of a small special lathe, the coned part E also fitting the spindle. The front end of the chuck is slotted to receive rollers L, L, and when these two rollers come together in the chuck (the centre point C of the rollers L, L comes exactly in the centre line of the chuck itself) each roller is curved on one edge, so that when the two come together in the position shown, the curved form on the two rollers shall be the curve that is required upon the head of the finished rivet. These rollers rotate upon the pin F, which is made a driving fit in the chuck, but a loose fit in the rollers, and secured by the nut S. Assuming the chuck and rollers to have been fitted up perfectly true, it will be readily understood that, when the whole rotates together, the joint line C between the rollers, and the centre of the transverse hole in the rollers, will both be in perfect alignment, with the centre line through the chuck and lathe spindle.