Patent GB-557570-A (GB)
Title: Improvements in or relating to lathes
IPC: B23B5/00
Filed: 1942-06-02
Abstract: 557,570. Lathes. BEST, C., RUAU, F. F., and MOLINS MACHINE CO., Ltd. June 2, 1942, No. 7477. [Class 83 (iii)] A lathe for turning hollow work pieces such as cartridge cases for small arms ammunition has means for rotating the work-piece by engagement with its bore and for determining the axis of rotation of the work-piece from its exterior surface so that surfaces such as an extractor groove are turned concentric with the exterior surface. In one form a bed plate 1 has a fixed headstock 2 carrying a hollow spindle 3 which encloses a slightly flexible mandrel 5. An extension bracket 6 on the headstock carries ballbearing steady rollers 7, Fig. 3, and a fixed tool 8 of notched disc type which trims the skirt of the case W as shown on the right of Fig. 22. On the right, Fig. 1, of the tool 8 is a form tool 11 which is secured to a slidable rod 12 and which serves to trim off the flange and turn a groove at the left-hand end of the work-piece, Fig. 22. The rod 12 is reciprocated in a guide 13 by a cam 14 on a cam shaft 15 and the upper end of the rod is stiffened by linkage extending from a bracket 25. A rod 29 is reciprocated in a bracket by a cam 36 and carries a rotatable push-rod 33 which can engage and rotate with the end of a work-piece. The work-pieces are supplied from a hopper 46 which may be as described in Specification 545,661 and delivers blanks singly base downwards through tube 47 to a member 48 reciprocable in a slide 49. A transfer device 45 including a blank receptacle 51 is swung through 90 degrees by a cam 38 on the cross shaft acting through lever 40 and link 43. In the receiving position the transfer device pushes back the member 48 so that a blank falls into the receptacle and is then transferred to a horizontal postion, Fig. 1. At the beginning of the operation a stop collar 52 on the mandrel engages the end of a cap 53 under pressure of a spring 54. In this position the push rod 33 is moved to the left and pushes the blank on to the mandrel, the transfer device then being moved away. Further movement of the push rod moves the mandrel and blank to the left to the Fig. 1 position. As the blank moves past the tool 11 the flange is turned off by this tool which is then moved inwards by the cam 14 to form the groove, The skirt of the blank is also trimmed by the tool 8 as the push-rod reaches the end of its stroke. The push-rod is withdrawn and the blank is then ejected by the end of a rod 56 passing through the mandrel and operated by a cam 62 and lever 58. The machine is driven from a transverse shaft 63 connected to the cam shaft by worm gearing 65 and to the mandrel by bevel gearing 67 and belt 71. Alternatively the cam shaft and spindle may be respectively driven independently by low and high speed motors. The cross shaft 34 is driven from the cam shaft through bevel gearing 73 and chain gearing 77 while a further chain drive 79 from the cross shaft operates the hopper. In a modification, Fig. 6, a mandrel 81 is secured to the spindle by a collar 83 and instead of using an axially movable mandrel the headstock itself is slidable in guides 86, up to a stop screw 93. Another headstock supports a rod carrying a. rotatable pusher 96 normally urged rearwardly by a spring 97 but moved to push a blank on to the mandrel by a cam 99 and lever 102. A bracket 92 supports steady rollers 109 and carries a shaft 112 supporting a lever 114, Fig. 8, operated by a cam 116 and carrying a tool 118 which trims off the flange during axial movement of the blank and is then moved inwards for the forming operation. A fixed tool secured to the bracket machines the skirt of the blank. An ejector mechanism similar to that described above ejects the finished blank. In both modifications the rollers are adjusted slightly nearer to the blank axis than would normally engage them with the blank so that the mandrel is slightly displaced and the blank firmly pressed against the rollers during machining. The rollers may be slightly convex at the ends nearer to the push rod. The mandrel may be barrel-shaped or shaped to fit the exterior of the blank and is preferably knurled. The mandrel end may be split, Fig. 12, and the ejector rod 135 tapered so that movement to the left expands the mandrel. In a further modification a chuck 140 has three jaws 143 separated by springs and having a groove 145 fitted with a friction ring 146, Fig. 17, in which the work advanced by the pusher is gripped after which further movement closes the chuck to grip the work. Modified forms of friction ring 146 are described. The work is supported in its interior by a flexible mandrel as in the previously described modifications. The chuck rotates freely in ball bearings 149 or it may be driven by a separate pulley 150 to relieve the load on the mandrel. The skirt is trimmed by a tool mounted in a holder 151 which may either be reciprocated or fixed so that the operation is performed as the work is pushed into the chuck.