Patent GB-190209361-A (GB)
Title: Improvements in and relating to Screw Cutting Lathes.
Inventor: PARKINSON ERNEST
Filed: 1902-04-23
Granted: 1902-11-20
Abstract: 9361. Parkinson, E. April 23. Lathes.-A screw-cutting lathe is provided with automatic means for disengaging the half-nuts from the leading-screw at the forward end of the traverse of the saddle, returning the saddle at a quick rate and again engaging it with the screw, withdrawing and moving forwards the tool at the required times, setting the cut, and interspacing the tool after each traverse when cutting multiple threads, the same cut being taken over each thread before alteration. A pair of co-axial discs 18, 18<A>, Figs. 1 and 2, connected together, are frictionally driven from the main spindle through chain gearing 25, and can make half revolutions when a lever 16 is alternately disengaged from stops 17, 19 on the plate 18. The lever 16 is rooked in opposite directions by the engagement of the saddle with dogs 10, 11 on a bar 9 pivoted to a lever 12 connected to a rock-shaft 15 on which the lever 16 is mounted. A link 26 pivoted on the disc 18<A> is connected to an arm 27 on a shaft 28 on which is feathered an arm 29 moving with the saddle and linked to the surfacing-slide to withdraw and bring up the tool at opposite ends of the traverse of the saddle. The front of the surfacing-slide is connected by a link 32, Fig. 4, with an arm 33 loose on a cam spindle 35 but capable of being connected to it by a pin passing through a fixed' arm, so that the cam-plate 36 is rocked to engage or disengage the half-nuts simultaneously with the bringing-up or withdrawal of the tool. The lever 12 is also connected to a cross-shaft 47, which is rocked to operate a clutch on a back shaft 74 connected by chain gearing 50, Fig. 2, to a shaft 44, on which is feathered a bevel frictionwheel 41, capable of engagement with a similar wheel 42 for quickly returning the saddle by means of gearing and the rack 8. The wheel 41 is pressed into engagement by a spring plunger and withdrawn by a cam quadrant 40 linked to the arm 33. The discs 18, 18<A> are temporarily held in a position intermediate between those determined by the stops 19, 17 by a hooked lever 55 and notch 20, this lever being tripped by one of a number of pins 57 on a disc 56 driven from the leading-screw 1, each pin representing one or more complete revolutions of the screw, so that the half-nuts are only allowed to engage at an integral number of revolutions of the screw determined by the pitch of the screw being cut and that of the leading-screw. The cut is put on by a pawl 66, Fig. 7, operating a ratchet-wheel 67 on a nut 68 on the feed-screw of the tool slide, the pawl being carried by a lever 66<A> rocked by a sliding rack 69, having a pin P engaging a slot in a block B angularly adjustable on the saddle. When cutting multiple threads, a guard ratchetwheel 67<A> is loosely mounted on the nut and provided with deep teeth separated by one or more shallow teeth according to the multiple thread being cut, so that the feed-nut is only operated after a cut has been taken off each thread. When a sufficient depth of cut has been reached, a coned rod 73 on the tool slide trips a lever 71 on the surfacing - slide and releases a spring arm 72, which raises the pawl by engaging a pin 66 on it, thus stopping the feed. The mechanism for transferring the tool from one thread to another, say in cutting a double thread, comprises a collar 77, Fig. 15, loose on a collar 75 screwed on the lathe spindle, and carrying a driver plate. The collar 75 has notches 76 corresponding in number to the multiple thread to be cut. The collar 77 is rotated by a hooked lever 87 engaging the notches 76, and is held stationary by a brake strap 78 when the lever is disengaged, allowing the lever to engage successively the various notches. A lever 80 on the shaft 28 is linked to a lever 82 pivoted on a plate 83 on the headstock and carrying a catch 84, which withdraws a spring catch 85 when the levers 80, 82 are rocked during the withdrawal of the surfacing-slide, and thus allows a spring plunger 86 to rise and disengage the lever 87 from the notch 76. Cam portions 88 between the notches move the hooked end of the lever farther out till a lug 89 on the lever operates a lever 90 connected to a lever 93 for re-setting the plunger, the hooked lever then engaging the next notch 76 and thus transferring the tool from one thread to the next.