Patent GB-505786-A (GB)
Title: Improvements relating to screw thread milling machines
IPC: B23G1/32
Filed: 1937-11-19
Abstract: 505,786. Milling screw-threads. SMITH & SONS (MOTOR ACCESSORIES); Ltd., S., and WOODHAMS, G. H. Nov. 19, 1937, No. 31846. [Class 83 (iii)] A screw-thread milling machine for producing two threads simultaneously on a rotary work piece has a clutch adapted automatically to impart to the work during each cycle of operations an angular movement exceeding one revolution and means for feeding two milling cutters axially and transversely relatively to the work. The machine comprises a headstock b carrying the rotary work-spindle c driven from an electric motor (not shown), in the machine base through belts, pulley o and worm gearing p. A sleeve g, Fig. 5, loose on the spindle, is driven by the worm and carries a ratchet wheel y, Figs. 5 and 11, adapted to co-operate with a pawl z pivoted on a disc h secured to the spindle. A spring 9 tends to force the pawl into engagement with the ratchet but may be prevented from operating by a spring catch 11 coacting with a pin 12 on the pawl, and a control for the pawl is provided by an axial pin 8 on a disc 2 which is loose on the sleeve g but may be rotated by the disc h through a ball 3 thereon engaging a recess 4 in the disc 2. When the machine is in position for starting operation on a workpiece j on the spindle c, a shoulder 6 on the disc 2 is in contact with a'fixed stop 7, and the operator releases the catch 11 to allow the pawl to engage the continuously rotating ratchet, whereupon the disc h and the work are rotated in the direction of the arrow in Fig. 11. When the ball 3 engages the recess 4 the disc 2 is carried along with the disc h until it is arrested by a shoulder 5 engaging the stop 7, after which the work continues to rotate until the pawl rides under the pin 8 on the disc 2 to disconnect it from the ratchet and allow it to be latched by the catch 11. The parts are so arranged that the work will rotate slightly more than one revolution before being stopped, and if rotation does not cease when the pawl is disengaged a dog 10 on the disc h comes into contact with the pin 8 to stop the rotation positively. The two cutters i for forming threads simultaneously on the parts j<1>, j<2> of the work are mounted on spindles f rotatably carried in rockers d attached to shafts a which are slidably and rotatably mounted in the headstock and are provided at one end with toothed fingers t respectively engaging lead screws u adapted to rotate with the work. The fingers t are carried by brackets v rotatable but axially immovable on the shafts s and the two lead screws u may be of different pitch or opposite hand. The shafts 8 are rocked to feed the cutters into the work by levers e, Figs. 2 and 6, loose on the shafts but having forks engaging webs 15 on the rockers d, the levers carrying trunnions 13 co-operating with nuts 14 on a right- and left-handed screw 18 rotatable by a hand wheel 20. The screw is freely supported by adjustable screwed bushes 19 in the headstock and washers 21 are spring-pressed. against the ends of the bushes to form adjustable stops for engaging the nuts to limit the depth of cut. The cutter spindles are rotated by pulleys r and belts connected to pulleys in the base of the machine. In operation, rotation of the work is started by the operator tripping the catch 11, the cutters are fed in by rotation hand wheel 20 and the threads are cut on the work during one revolution thereof whilst the cutters are traversed axially. When the pawl z is automatically tripped to stop rotation of the work, the cutters are withdrawn by operation of the hand wheel 20 and are returned axially by reverse rotation of the work spindle c through a hand wheel x thereon. During this reverse rotation the dog 10 engages the pin 8 and carries the plate 2 with it until the shoulder 6 on the plate meets the fixed stop 7 to arrest the plates and spindle ready for changing the work. Instead of cutting threads on the two parts j<1>, j<2> of the work, of different diameter, threads may be formed simultaneously on inner and outer surfaces of the work or on two inner surfaces of different diameter, and the cutters may be mounted on slides instead of levers. Specification 303,671, [Class 83 (iii)], is referred to.