Patent GB-706542-A (GB)
Title: A device for controlling the cutting of simple or multiple thread screws on screw cutting lathes
IPC: B23G1/02
Filed: 1952-07-23
Abstract: 706,542. Screw-cutting lathes. CRI-DAN. July 23, 1952 [July 25, 1951 ; July 5, 1952], No. 18685/52. Class 83 (3). [Also in Group XXIV] Means in a screw-cutting machine for cutting single or multi-start threads comprises a ratchet-wheel 8 rotated by one or more teeth at each revolution of the shaft 1 of the pitch-cam, a ratchet-wheel 31 for feeding the tool, and interlocking means between the wheels so that the feedwheel is not actuated until all threads have been cut to the same depth. A cam 2 on the shaft 1, which also carries the cam which determines the pitch-feed of the tool carriage, rocks a lever 3, 3' carrying a pawl 7. The pawl 7 advances the ratchet-wheel 8 by one or-more teeth according to which of two positions an abutment member 15 occupies. If a single-start thread is to be cut, the pawl 7 is locked in an ineffective position by a catch 22. The lever 3, 3' also carries a pawl 26 which advances the ratchetwheel 31 to feed the tool between each cut when a single-start thread is to be cut. For cutting multistart threads, a member 25, pivoted coaxially at 27 with the pawl 26, is locked by a pin 28 to engage it with a notch 36 in a disc 37. With the member 25 thus positioned, the first contact of the cam 2 on 'the lever 3, 3<SP>1</SP> rotates the wheel 8 and the wheel 31. The wheel 8 is fast with a wheel 10 which carries round a pawl 50 on the disc 37 which is urged counterclockwise by a spring anchored to the machine frame. On the return movement of the lever 3, 3' the lever 25 only is moved and is forced out of the notch 36, thus releasing .the pawl 26. The next movement of the lever 3, 3<SP>1</SP> therefore advances the wheel 8 but not the feed-wheel 31. Successive movements of the lever advance the pawl 50 until a pin 55, on an arm 57 clamped in a position determined by a scale 58, strikes a lever 53 integral with the pawl 50 to release it. A spring-urged lever 62 engages the lever 53 to maintain it in a disengaged position. The disc 37 is immediately returned by its spring to its initial position. At the end of the movement of the disc 37 the retaining lever 62 is released by a fixed pin 69 and the disc is brought to rest by stationary abutment 66. The cycle is then repeated so that each thread is cut to one depth before the tool is fed in to take a subsequent cut. A device 70 is positioned against a scale on the wheel 31 according to the depth of cut required. The device actuates a switch to energize electrical means 46 which advances a masking plate 38 to release the pawls 26, 33. A spring then returns the wheel 31 to its initial position and the cutting operation is complete. In a modification, the cam 2, Fig. 8, reciprocates a slide 75 carrying a pawl 77 engaging a ratchet 'wheel 80 bearing a pin 88. The wheel 80 is mounted on a spindle 81 which also carries an adjustable disc 84 bearing a projection 89. A disc 87 is mounted freely on the spindle 81 and carries a finger 86 which is movable between the pin 88 and the projection 89. For multi-start threading, the disc 84 is set by a scale 112 and the finger 86 engaged in a notch 91 of a spring- pressed lever 92. When the cam 2 has reciprocated the slide 75 the required number of times and all threads are thus cut to one denth, a projection 85 on the disc 84 pushes a slide 100 to the left to advance the feed wheel 104. Simultaneously, the projection 89 engages the finger 86 which pushes away a retaining pawl 95 and allows a spring 96 to return the disc 84 to its initial position. For single-start threads, the two slides 75,100 may be secured together.