A twenty-four-inch metal spinning lathe that is rigged up in a modern way, is shown in Fig. 32. The hand wheel of the tailstock has been discarded for the lever A, which is more rapid and can be manipulated without stopping the lathe. This lathe has a roller bearing for the center B which is a practical improvement over types previously used. The pin C, which is used in the rest as a fulcrum for the spinning tools, is also an improvement, being larger than those ordinarily used. It is ¾ inch in diameter, 6 inches long, and it has a reduced end for the holes in the rest, ⅜ inch in diameter by 1 inch long. This pin is large enough so that the spinner can conveniently hold it with his left hand when necessary, and it can also be rapidly changed to different holes. The pins ordinarily used, because of their small size, do not have these advantages. The speed of a spinning lathe having a five-step cone should be about 2,250 to 2,300 revolutions per minute with the belt on the smallest step, and from 600 to 700 revolutions per minute with the belt on the largest step. The fastest speed given is suitable for all work under 5 inches in diameter, and the slowest for work within the capacity of the lathe. On large shells it is sometimes necessary to change from one speed to another as the work progresses. Figs. 33 and 34 show the spinner at work, and illustrate how the tool should be held, and also the proper position of the left hand.
Fig. 33. View showing how the Tool is held when Spinning
Fig. 34. Another View showing the Position of the Spinner and the Way the Tool is held when forming the Metal
Construction of the Tailstock and Back-center
Fig. 35 shows a spinning-lathe tailstock, which has been changed from the hand-wheel-and-screw type to one having a lever and a roller bearing. The spindle A which is withdrawn from the lever and turned one-quarter of a revolution to give a better view of the rollers, is made from 1¾-inch cold rolled steel. The rollers against which the center bears do not project beyond the spindle, so that the latter can be withdrawn through the tailstock. This eliminates the excessive overhang caused by ball bearings and other centers. When the center projects too far, the tailstock cannot be set close to the work owing to the necessity of withdrawing the center when removing the spun part. The application of this principle to a spinning lathe is original and the type of center illustrated was used only after all other kinds had failed, including all the types of ball bearings and revolving pins. The best forms of ball bearing centers do not last over a year, if in constant use, and they will not always revolve on small work. Two other spindles are shown in this engraving, which were taken from other lathes in order to show different views of the parts. The cylindrical pieces B are the hardened friction rollers which belong in the slot of the spindle F, and C is the hardened pin upon which they revolve. The hardened center D has a threaded end on which the back-centers E of different lengths and shapes are screwed. The friction rollers should always be in a vertical position, and care should be taken to have them exactly central with the spindle.