Patent GB-164387-A (GB)
Title: Machine for making milling cutters
IPC: B23B5/42
Filed: 1919-12-03
Abstract: 164,387. Marks, E. C. R., (Pratt & Whitney Co.). Dec. 3, 1919. Backing-off lathes; milling-lathes.-In a backing-off lathe for finishing milling-cutters with inclined teeth of any non-rectilinear profile, after each complete revolution of the grooved blank the rotation of the spindle is stopped with the tool opposite one of the grooves in the blank, and the backing-off movements are stopped simultaneously. The carriage is then fed longitudinally, a slight rotation being given to the blank in the case of helical teeth, and immediately before this longitudinal feed the tool slide is withdrawn together with the follower. After the feeding-movement, the tool slide and follower are returned gently, and the blank resumes its rotation. The relation between the backing-off action and the rotation of the blank is varied in accordance either with the longitudinal inclination of the teeth (by the sup. plemental rotation of the blank mentioned above) or with the angle between the cutting surfaces of the teeth and radial planes. The main slide 24 on the carriage 21 carries a follower 27 engaging a former 26 secured by bolts 36 to an adjustable carriage 29. A slide 38, adjusted by a handwheel 40, carries the tool-holder 42, and tool 25 (for which a milling-cutter may be substituted) held by a wedge 45 so that its upper face 44 is level with the axis of the blank. The backing-off cam 46 is carried by a shaft 47 and moves the slide 37 by means of a lever 51. The shaft 47 is driven by a bevel-wheel 75 on a shaft 71 rotated through worm gearing 69, 70 by a shaft 65 which is driven through bevel-gearing and change-wheels from the transverse shaft 11, which drives the spindle 5. The cam 46 is given one complete rotation for each tooth of the blank. In the case of undercut teeth, the requisite retarding action on the motion of the tool is obtained by connecting the bevel-wheel 75 to the shaft 71 by camgrooves 71<1>, Fig. 20. The same effect may be obtained by other means, as by using a follower 27s with its acting face shaped as shown in Fig. 26, this face co-operating with a surface 26t on the former, which is given the same angle as the angle of undercutting of the teeth. The supplemental rotation of the blank is obtained by means of a worm wheel driven by the shaft 11 and secured to a sleeve 79 inside which slides a shaft 83 formed with rack-teeth engaging a pinion 86. The shaft 83 is slid as the carriage 21 moves along the bed by the action of a rod 104 and a bracket 102 clamped to the rod by handles 106; the pinion 86 is thus rotated and thereby, through change gearing (not shown), rotates a worm 91 giving the requisite supplemental rotation. By loosening the clamps 106, the rod 104 slides freely through the bracket 102 and the above-described action is stopped, as would be required for cutting straight teeth. The carriage 21 is fed by a screw 107 which may be turned by a hand-wheel 114, acting through bevel-gearing 113 and a short shaft 112. The power feed is given by one or other of two ratchets 133, 134, Fig. 11, which give a quicker and a slower drive respectively of the shaft 112, operated by a link 124, arm 125, rockshaft, arm 128, and roller 129 engaging a cam 130 on a shaft 131. The alternate rotation of the spindle 5 and feeding of the carriage 21 is obtained by the action of a clutch 138 which connects the shafts 11, 131 alternately with the main driving-shaft 135; in each case after one revolution the clutch is thrown over by the action of cams connected with the shafts 11, 131 and locking catches 168, 169. The drive to the shaft 11 is through a wheel 141, round which is an adjustable sleeve 142 carrying a pinion 144 which can be put in gear with any one of a set of toothed wheels on a shaft 145 which drives the shaft 11, the speed of which can thus be adjusted. The withdrawal of the tool 25 and follower 27 is effected by a cam 182 on the shaft 131 operating a slide 184 through a lever 181. This slide 184 is movable independently of the slide 24, but is locked thereto during this withdrawing action by a plate 186 drawn downwards by hooked levers 188 moved by a cam-sleeve 189 operated from the shaft 131. Before the slide is returned, cam-operated rollers 200, 201 are brought into action to take the weight of the slide 24 off the slide 184, whereupon springs 206 return the slide 24, the motion being damped by fluid such as oil in the chamber 211. A suitable relief valve is arranged so that the quick withdrawal is not damped. With slight modifications of the mechanism, a former may be used which is the reverse of that shown, i.e. one which gives the profile to be cut instead of that of the cutter; and a milling-cutter may be used as the cutting-tool. Specification 164,388 is referred to.