Patent GB-238584-A (GB)
Title: Improvements in gear hobbing machines
IPC: B23F5/12
Filed: 1924-03-24
Abstract: 238,584. Herrmann, K. L. March 24, 1924. Gear-cutting.-In a machine for bobbing gears the work-spindle 1, journaled in a bearing 5, is connected to the driven hob spindle 3 through an adjustable transmission shaft 2, and is moved axially at a variable speed by screw-and-nut mechanism to carry the work past the hob. The work 4, consisting either of blanks or of roughly cut gears, is secured on the arbor 41 by a nut 81, and the spindle 1 is driven through a gear 7 which engages a long pinion 8 on the transmission shaft. The gears 7 and 8 may be changed when required, the bearing 14 of the transmission shaft being adjustable through the slotted connection 14b for this purpose. The hob spindle 3, mounted in a pivoted bracket 11, is driven by bevel gearing 12 from the transmission shaft and is angularly adjustable about this shaft by means of a screw 22 provided with an indicating-dial 23 and engaging the chip and oil pan 36 secured to the bracket. The latter is secured in adjusted position by bolts 11<a>, 11<b>. The hob 20 is driven through a gear 25 formed on a fly-wheel 24, and driven by a pinion 26 on a shaft having fast and loose belt pulleys 30, 29, connected to an electric motor or other power drive. In order to prevent the work-spindle from over-running its drive and to take up backlash in the driving gears, the gear 7 is braked by means of a pinion 32 engaging the gear and having a drum engaged by a spring brake-band 34. The work-spindle is fed across the hob by means of an axially fixed screw 15 threaded into a nut secured in the work-spindle. In order to vary the speed and direction of this feed the screw 15 carries a wheel 42 driven from a reversible electric motor 44 controlled from a handle 48 on the front of the machine, the circuit of the controller being shown in Fig. 7. The handle carries contact strips 59, 60, while the member 47 is provided with contact strips arranged as shown and also with armature resistances 65. 66 and field resistances 72, 73 for a shunt-wound motor having an armature 50 and field coils 51 and supplied from mains 52, 53. When the controller is moved to an advance position in the direction of the arrow, the armature resistance coils 66 are first successively cut out and then the field resistances 73 are put in, thus progressively increasing the speed of the motor. A similar increase of speed in the reverse direction is obtained bv movements of the controller handle in the direction of the reverse arrow. The screw 15 is prevented from turning when the. motor 44 is not running by means of a friction shoe. In order to align the teeth of roughly cut gears with the teeth of the hob ; the mandrel 41 is provided with a collar 75 notched at 77 to receive projection 78 on a gauging-member which is formed with a cylindrical portion 79 adapted to fit into a tooth spcace of a cut gear. In operation a finished gear is placed on the mandrel in correct engagement with the hob teeth and the clamping nut 81 tightened. The gauge is then placed in notch 77 and in one of the tooth spaces of the gear and the collar tightened in this position by a screw. Roughly cut gears may then be correctly positioned by fitting the gauge between the notch in the collar and one of the tooth spaces of the gear. The machine is automatically stopped by means of a spring-pressed shifter-rod 84 which is normally held to retain the belt on the fast pulley by means of a catch 92 on a rod 89, which carries an adjustable projection 96. On completion of the work by forward movement of the work-spindle, a projection 97 on the wheel 7 engages the projection 96 to rock the rod 89 and release. the rod 84 to stop the machine, the projection 97 being so placed that the work-spindle stops with the gauging notch 77 in its uppermost position. The control lever 48 is then moved to its reverse position to drive, the screw 15 to return the work spindle whereupon the finished gear is removed, a fresh gear positioned, and the control lever is moved to the advance position to bring the work quickly up to the hob. For the working feed the motor 44 may either be stationary or rotated to drive the screw 15 at a predetermined speed in either direction according to the rate of feed required.