GB520050A - Improvements in tapping and screwing machines - Google Patents

Abstract

520,050. Screwing; tapping. MOSSAY, P. R., and MOSSAY, P. A. H. Oct. 19, 1938, No. 30256. [Class 83 (iii)] A screwing or tapping machine has the spindle rotated by a reversible electric motor and provided with a lead screw engaging a stationary nut, the lead screw carrying adjustable dogs for operating limit switches to control the motor at both ends of the spindle traverse after it has been started by a manually controlled switch and the switches are arranged close to the tapping spindle so that they may be operated directly by the dogs thereon. The motor shaft 8 carries a part 9 of a friction clutch whose other part 10 is spline d at 20 within a hollow lead screw 21 co-operating with a fixed nut 23 and constituting the tapping spindle. A set screw 241 secures the nut and allows the lead screw and nut to be changed readily. The friction clutch is arranged to slip on overload. Adjustable nuts 25, 25 on the lead screw are adapted to engage the ends of a spring 32 which acts on plungers 29, 30 engaging the limit switches 27, 28 which control the motor. Three circuit diagrams are described, in the first of which, with the switch 27 closed and switch 28 open, depression of a foot switch actuates a contactor to start the motor in the forward direction to feed the tool downwards. The switch 28 then closes and the tool descends until the nut 25 opens the switch 27 to stop the motor. The operator then changes over the foot switch and the motor is reversed to raise the tool until the switch 28 is opened by the nut 26. In the second example, the switch 28 is normally open and switch 27 is held open by the' nut 25 in its lowest position. Depression of the foot switch closes a contactor for starting the motor in the reverse direction to raise the tool. The switch 27 then closes and the tool ascends until the nut 26 closes the switch 28 to throw over the contactor and reverse the motor to cause the tool to descend, the switch 28 opening but the contactor being held by a retaining contact. At the lower limit of travel the nut 25 opens the switch 27 to reverse the motor, and the tool continues to reciprocate until the foot switch is released. When the foot switch is opened and reclosed, the tool finishes its stroke and is then stopped by one of the limit switches. In the third circuit, a two-position foot switch controls the coils of two contactors for actuating the motor in' opposite directions, and operates in the same manner as the second example. A magnetic brake is operated as soon as the motor circuit is broken.