GB592069A - Improvements in or relating to machines for cutting grooves in metal - Google Patents

Abstract

592,069. Rifling ; rifling-bars. BIRMINGHAM SMALL ARMS CO., Ltd., WOOD, A. E., and BRANFIELD, H. C. May 3, 1945, No. 11212. [Class 83 (iii)] In a machine for cutting an internal groove in the bore of a metal workpiece, the work-piece and tool are relatively reciprocated and the tool is moved into cutting position by a member which is caused to rotate inside a hollow cam-member ; one or more grooves, varying in depth along their length, may be cut and means are provided for retracting the tools from the bottom of each groove during the return stroke and for increasing the depth of cut step by step until the required depth is machined. The work-piece, such as a gun barrel B, the firing chamber of which is to be grooved, is mounted on a work holder 79 on a reciprocating table 1 which also carries a bracket 3 supporting a sleeve 5. A hollow tool bar 15 is secured to a sleeve 11 fitting inside the sleeve 5 and supported by a stationary bracket 9. Four cutting tools are fitted in slots in the bar 15, Fig. 5, and are urged to an inoperative position within the slots by a spring-pressed plunger 25 co-operating with sloping faces 29 of the slots ; to facilitate insertion of the tools, the plunger can be moved against the spring by the rod 26. A rod 33 slidable in the bar 15 has a coned end engaging sloping faces 21 on the tools and its axial movement determines the depth of cut. The rod 33 is screwed into a draw-bar 35 splined at 91 to a draw-sleeve 37 which is splined at 87 to the sleeve 11 and has an internal thread engaging a threaded sleeve 69 rotatable on the draw-bar 35. The sleeve 69 has another thread, of opposite hand, engaging an internal thread on a bushing 39 splined at 89 in the sleeve 11 and within which a flanged nut 41 on the threaded end of the bar 35 bears on an internal shoulder 43. A plate 45 journalled on the nut 41 carries a pawl 51 engaging a ratchet plate 55 secured to the nut 41 and a locking pawl 81- is mounted on the bushing 39. The draw-sleeve 37 is actuated by a cam track 7 in the sleeve 5, Figs. 4, 11, through a roller 67 on a nut 63 engaging a screw-thread 61 on the sleeve and axially restrained in the sleeve 11 by ball bearings 65. The screwed sleeve 69 is actuated by a cam track 77 carried by the table 1 through a roller 75 and the nut 41 is actuated by a further cam track 59 carried by the table through a roller 57 on the plate 45'and the pawl and ratchet 51, 55. In operation, from a position about midway of a return stroke, the table 1 moving to the right, the roller 75 clears the track 77 as the roller 67 enters the long straight portion of the track 7. The roller 57 has then entered the track 59 and rotates the nut 41 through the ratchet 55 so that the draw-bar 35 is moved to the right and the coned end of the rod 33 expands the tools by one stage for the following cutting stroke. At the beginning of a cutting stroke, the table moving to the left, there is no change of position of the tool setting parts until the roller 67 meets the rise a of the track 7 when the nut 63 is rotated so that the draw-sleeve 37 is moved increasingly to the right and through the sleeve 69 moves the bushing 39, nut 41, draw-bar 35 and rod 33 to the right to expand the tools until the flat b on the track is reached. On the fall c the tools are retracted so that a groove of somewhat arcuate form is cut. As the roller 67 moves along a, b, c, the roller 75 moves along the portion c of the track 77, and as it moves along the straight portion d the roller 75 in the portion f of the track 77 retracts the tool sufficiently to prevent drag on the return stroke. On the return stroke, the hump h of the track 77 restores the tools to the previous operative position as they begin to be advanced by another stage by the track 59. A shield 85 is adjustably mounted on the ratchet 55 to prevent further feed when the grooves have been cut to the required depth and may be adapted to operate a switch to stop the machine.