Patent GB-249938-A (GB)
Title: Improvements relating to the art of gear-cutting
IPC: B23F5/12
Filed: 1925-01-06
Abstract: 249,938. Barnes, J. H. Jan. 6, 1925. Gear-cutting; tools.-Helical, double helical, or straight spur gears, or the profiles of other powertransmitting bodies such as cams, racks, or segments, are finished by means of a tool which takes a continuous shave on a working surface in the direction of roll of the said surface, the desired profile being obtained bv means of master cams. The roughed gear is mounted on a spindle 9 carried in bearing members 6, 7 and locked against end movement by nuts 10, 11. A member 6<1> and the bearing 7 are respectively provided with loose segmental gears 16, 15 and fixed involute cams 20, 19. The front end of the spindle has a bearing surface 21 carrying a slide block which moves in guides 26, 27 on the tool holder 30 while the rear end of the spindle is guided by parallel guides 31, 32. The blank arbor is mounted in the conical spindle end by means of a longitudinal bolt 43 and the roughed blank is rigidly gripped between a slidable spacing-member 45 and a clamping-member 46 operated by a nut 47. The tool-holder comprises a -part-cylindrical casing 48 fitted with end portions 29, 33. The end 29 carries opposed rollers 51, 52 bearing on the cam 19 and the end 33 carries similar rollers bearing on the cam 20, so that as the toolholder is oscillated the required tooth-forming movements are imparted to it by means of the fixed cams, these movements being permitted by the slide connections between the tool-holder and spindle. In order to oscillate the tool-holder the gear segments 15, 16 are respectively connected to the members 29, 33 by means of links 61, 65, both ends of the tool-holder being thus synchronously driven. The segmental gears 15, 16 mesh with segments mounted on a shaft 123 which is rocked by means of a rod 129, Fig. 4, connected to an adjustable crank-disc driven by worm gearing 138 from a shaft 139. The latter carries a clutch 145 operated by a hand lever 149 and is driven from a motor 168 through a pulley 148. The machine is automatically stopped after a complete revolution of the blank by means of a link 157 which is pulled upwards by a spring 158 and which is connected through further levers to a pin coacting with a depression in a ring 163 on the spindle. The main drive may be disengaged manually at any time independently of the automatic stop mechanism. Inspection plates 166, 167 are provided in the main supporting housing. The surfaces 67, 68 of the cam 19, Fig. 22, form parts of involutes struck from a circle 66 of the same diameter as the gear to be cut, the contacting rollers being located on a tangent to this circle so that the distance across the cam is constant and the edge 74 of the'tool 73 mounted in the holder describes an involute surface. On the return movement a second cutting-edge 77 will finish a second involute surface of the blank, For spur gears the cutting edges of the tool are parallel to the blank axis but by using tools having incline, cutting edges, helical teeth may be cut. For cuttit.,.; double-helical teeth, the tool shown in Fig. 14 is employed. In another form, Fig. 12, two cutting edges 88, 89, may operate on adjacent teeth in the same working movement. The roughing of the teeth before finishing may be effected by hobbing, a slightly undercut toothform being preferred. The shape of the cam surfaces may be modified if desired to vary the tooth form. The tools are mounted in guides 99 and are secured by a bolt 100 coacting with a cam plate 101. Adjustment is effected by a threaded member 102 mounted in a positioning block above the tool 84. The rough gear is positioned on the arbor by means of a segment 114 which is mounted on a lever arm 112 and is swung upwardly to locate the blank, which is then clamped in position. A protecting plate 116 fitting over the member 45 is mounted in guides 117 on the tool-holder and serves to protect the internal mechanism from cuttings. In order to index the blank, cams 173, 174, Fig. 7, on the tool-holder coact with a pivoted aim 171 connected to a slide 178 having a pawl 183 engaging a ratchet wheel 36 on the spindle so that when a single toothed cutter is used the blank is rotated one tooth for each forward movement of the arm 171. In order to brake the movement of the spindle, a member 186, Fig. 8, coacting with a brake drum 34 on the spindle is moved upward at the required moment by an oscillating cam-plate 188 actuated through a link 192 by cams on the shaft 136. In order positively to arrest the motion of the spindle, a stop wheel 35 coacts with a stop 202 fixed to the slide 178, the timing being so arranged that the stop is brough, into engagement with the wheel as soon as the indexing movement is completed. An index plate 37 on the spindel coacts with pivoted locking-dogs 206 which are connected to the cam 188 and serve to determine the exact position of the spindle, the dogs being withdrawn by the cam at the correct moment to permit the indexing movement to take place.