Patent GB-585187-A (GB)
Title: Improvements in or relating to screw thread milling machines
IPC: B23G1/32
Filed: 1944-10-20
Abstract: 585,187. Milling screw-threads. PADWICK, R. C., and PLESSEY CO., 'Ltd. Oct. 20, 1944, No. 20351. [Class 83 (iii)] A screw-thread milling machine has a hydraulic system for traversing a work-carrying head to and from the loading and working positions and has mechanical gearing including a disengageable clutch for returning the head to loading position after it has been in the working position for a predetermined time. The work is secured in a rotary collet 101 in a head 19 and the cutter 30<1> having annular teeth is carried by a stationarily mounted rotary spindle 30 which is driven by cone pulleys and a double belt from an electric motor. The head 19 is fed by the piston 22 of a hydraulic cylinder 12 supplied with fluid from a sump 2 by a motor-driven gear pump 1 connected by pipe 4 to a reversing valve 5. In operation, with the parts as shown, fluid is delivered by the pump and pipes 13, 15 to both ends of cylinder 12, the pipe 15 leading through a trip valve 14 and pipe 15a. Owing to the right-hand end of the piston 22 being of larger area than the left, the head 19 is traversed on an idle return stroke at high speed and then held against a stop, the work being non-rotating during this movement. After changing the work in the collet 101, the operator depresses a knob 6 to actuate reverse valve 5, thus connecting pipe 15 freely to exhaust and allowing pressure from pipe 13 to feed the head rapidly towards the cutter. A catch 35 on a lever 36 attached to valve 5 engages a spring latch 34 to hold the valve in this position. On nearing cutting position a roller 48 on linkwork 46, 42 rides into a recess 21 in a ramp 20 on the head to allow a spring 49 to actuate the linkwork and move valve 14 to the left to shut off pipe 15a. Exhaust from cylinder 12 then proceeds through byepass 16, non-return valve 18 and adjustable throttle valve 17 in order to reduce the speed of the head as it approaches a stop 102. On engaging the stop, the head remains stationary whilst cutting takes place with the work fed by a cam at the required pitch speed, and the roller 48 rides off the end of ramp 20 to allow the spring 49 to rock the link 42 further and cause a lever 38 attached to valve 14 to take up in a lost-motion slot 40 and rock a lever 26a to engage a clutch 26 with the constantly rotating cutter spindle 30 through change gears 27, 28. ' This causes a worm-shaft 25 to rotate a disc 23 carrying a dog 24, which, after one revolution of the disc, trips the latch 34 and allows a spring 51 to depress valve 5. This admits fluid by pipe 15 to valve 14, moving the latter to the right, and then proceeds by pipe 15a to cylinder 12 to return the head 19 to loading position. Simultaneously, movement of valve 14 to the right disengages clutch 26 to stop rotation of disc 23 and allow the latch 34 to hold lever 36 in raised position until the operator next depresses knob 6. The disc 23 makes one revolution whilst the work makes one and one-sixth revolutions. The work is driven at a low speed in either direction by a reversing drive from the shaft 25 so that it only rotates during the cutting operation. The collet 101 may be operated by fluid pressure from the pipe 4 or mechanically, and the Specification describes also a construction of machine.