GB419705A - Improvements in or relating to electrically controlled screw-tapping machines - Google Patents

Abstract

419,705. Screw-tapping. HERRMANN, R., and HERRMANN, E., 22, H÷lderlinstrasse, Stuttgart, Germany. March 23, 1934, No. 9182. Convention date, May 8, 1933. [Class 83 (iii).] In a tapping-machine the spindle of which is driven by a reversible electric motor, a mechanically controlled reversing switch is kept in the " off " position when changing from backward to forward rotation and after being set to move into the forward position, by a locking bolt with a flattened end. The tap spindle 1 driven through toothed gearing from a reversible electric motor 13 is mounted in a sleeve 4, which is capable of limited vertical feed through rack and pinion gearing driven by the motor through a train including worm and worm wheel 20, 21 respectively; the worm wheel 21 drives through a yielding friction clutch 33, Fig. 2 (section along A, B, C, D, E of Fig. 1), and pick-off gears 25, 26 are included in the train. The feed pinion 28 carried by a sleeve 34 which has a drum 33 at one end and is loosely mounted on the shaft 27 is driven therefrom through tappets 35, 36, Fig. 5, and ring springs 30, 31 arranged within the drum, the feed drive is thus yielding, being taken through the spring 30 for downward feed and through spring 31 for the return movement. The casing 33 carries adjustable stops 64, 65, Fig. 6, on its periphery which contact with an abutment 17 on a ring piece 60 arranged between the casing and the machine frame, Fig. 2 ; the ring piece is capable of limited rotary movement determined by a notch 62 and stop 63 and has a projection at its lower end which is adapted to engage a spring-pressed plunger 53 carried by a block 55 fixed to the end of a switch shaft 39. A hand-operated locking bolt 69 normally keeps the contact arms 41, 42 of the switch in the " off " position by a flattened end 70 on the bolt contacting a cut-away portion 71 of the block 55. The switch gear is in the position shown in Fig. 5 at the commencement of a tapping operation and on release of the locking projection 70 the plunger 53 moves the switch shaft 39 in a clockwise direction, thus engaging the forward contacts, Fig. 9 ; the feed motion operating through the yielding springs is arranged to be slightly greater than the screw pitch so that spring 30 is increasingly compressed during downward movement. The feed continues until the stop 65, Fig. 6, strikes the abutment 67 thus forcing the ring-piece 60 over the plunger 53 and finally allowing the latter to snap around to the left, thus reversing the motor and returning the spindle. The stop 64 finally moves the ring-piece in the opposite direction and the plunger 53 moves the switch to the " off " position where it is again automatically engaged by the locking bolt 69 thus requiring hand release of the bolt before another feed cycle can operate. Excessive resistance to cutting of the tap results in the drum 33 remaining stationary, but a further stop 68 fixed to the shaft 27 then operates to engage the projection 67 and thus reverse the motor.