Patent GB-553432-A (GB)
Title: Tapping machine
IPC: B23G1/16
Filed: 1941-07-07
Abstract: 553,432. Tapping machines. BAKEWELL, H. F. July 7, 1941, No. 8561. (Class 83 (iii)] A tapping machine is provided with a sleeve on the spindle having both a threading portion and a pilot screwed portion, the threading portion being arranged to cut threads on jaw-like members which then move on to the pilot portion and act as a stationary nut to control the feed of the tap. The tapping spindle 4, which may also be adjusted axially by rack-and-pinion gearing 5, 6 carries a guide screw 10 secured to the spindle and coacting with the stationary nut elements 11 a, 11b carried in a vertically-adjustable frame 13. The guide-screw comprises a gauging section 15 for positioning the nut elements, a fluted cutting section 16 for cutting the threads on said elements and a continuous pilot thread portion 17 for determining the feed. The nut elements are adjustably mounted in supporting arms 23 which are pivoted at 27 and are connected by spring links 29 to a solenoid-operated rod 30, the solenoid being energized to engage the nuts with the screw 17 against the action of the disengaging spring, the spring links serving to maintain the nut segments in firm engagement. When the work has been tapped to the required depth the spindle 4 is reversed and the tap withdrawn to a position clear of the work whereupon the segments are disengaged. The spindle is driven by a belt 37 from a reversible two-speed motor 35 controlled by the axial spindle movement through a switch 41 operated by abutments 47 on a counterweight 42 connected by a cable to the tool spindle. Levers 44, 45 medially pivoted to vertical rods 54 have their ends 49 engaging opposite sides of a switch-actuating pin 50 while the other ends of the levers are actuated by the. pins 47. In the upper position of the spindle, i.e. the lower position of the weight, one pin 47 causes the switch to be moved upwardly to the position shown in Fig. 1, while when the tap reaches the required depth in the work the other pin engages lever 44 and moves switch 41 downwardly to reverse the motor. To adjust the axial limits of spindle travel the rods 54 carrying the pivots are independently adjustable from hand wheels through worm gearing 58 and crank arms 57. The circuit of the motor which enables a complete cycle to be performed automatically is shown in Fig. 1. The motor speed is selected by a two-position hand switch 69. On closing master-switch 75 a pilot relay 76 is energized to close switches 76a, 76b. Switch 65 is then depressed to start the cycle by energizing relay 80 which closes contacts 80a, 80b, energizes solenoid 66 to engage the nut segments and also energizes one of the relays 67, 68 to drive the motor at selected speed. When the work is completed the switch 41 is tripped and this breaks the circuit of motor 35 via switch 69 and energizes relay 70 for high speed reverse rotation of the motor. When the tap has been retracted the switch 41 is shifted to the Fig. 1 position, the motor is stopped and the nut segment is released. Means are provided for ensuring that all operation is stopped at the end of a cycle, even if the switch 65 has not been returned to its Fig. 1 position. An emergency switch 71 may be closed at any time to stop the motor 35 and then reverse it out of the work and finally stop the machine. For setting the stops the tool spindle is lowered by the rack and pinion mechanism until the tap contacts the work and the hand wheel index 90 set to zero. The work is then removed, and the spindle lowered to the required depth of cut and the lever 44 adjusted to trip the switch in this position. The spindle 4 is then raised clear of the work and the lever 45 set so that it restores the switch when this position is reached. Lamp indicators 93, may be used in conjunction with this switchsetting mechanism. The frame 13 is adjusted so that the nut segments engage the pilot section 17 throughout the cycle. Preliminary to the tapping operation, the threads are cut in the nut segments by first setting them to depth by the gauge portion 15 and then cutting the threads by the part 16 of the screw 10. The spindle-head incorporates two speed mechanism. A splined clutch member 95 on the spindle is journalled in a cylinder 98, the piston 97 of which is operated by fluid pressure to engage the clutch either with a member 99 secured to the belt pulley for direct drive of the spindle or with a member 100 driven from the member 99 through back gearing including a shaft 103 for a low speed drive. When this drive is not required the shaft 103 may be moved laterally by a manual control 103d. The fluid pressure is supplied by a pump 105 which delivers to valves 110 which are dependently controlled by linkage from a spindle 117 so that when one side of the piston is open to pressure the other is open to exhaust The fluid pressure engagement of the clutch members also permits slip if a predetermined torque is exceeded. For this purpose a byepass valve in the fluid circuit is arranged to give any desired pressure, indicated by a gauge, on the piston 97. When resistance determined by the gauge setting, is exceeded the piston 97 yields and the operative clutch 99 or 100 disengaged.