GB809467A - An attachment for chasing threads on horizontal lathes - Google Patents

Abstract

809,467. Screw-cutting attachments for lathes. CICCARELLI, D. P. April 9, 1956 [April 8, 1955], No. 10697/56. Addition to 764,926. Class 83 (3). An improvement in the thread-cutting attachment of the parent Specification comprises a sliding spring-returned cam-bar 9, Fig. 3, for operating the transverse tool-carrying slide, and an adjustable automatic tool-advancing device for increasing the depth-of-cut. The bar 9 is arranged in guides 9a in the longitudinal slide of the attachment, and is spring-urged towards the right. A roller 8 on one end of the bar is engaged by a lip 4a, underneath the main-feedcam, to withdraw the tool-slide at the end of a cut. The other end of the bar has an integral wedge-piece 10 which engages a slot 9b in the transverse-slide to effect withdrawal. Automatic feed.-One form comprises a stop 28, Fig. 2, on the attachment-bed adapted to be engaged, on return of the carriage, by a depending member 21 pivoted to a cranked-lever 20 and engaging, in this direction of motion, a lug 20a on the lever. The latter is thus turned clockwise and a pawl 23 on the other arm of the lever moves a ratchet-wheel 19 to effect toolfeed. The ratchet-disc is geared through bevels 17, 16, Fig. 3, to rotate a cam-disc 15a which engages a peg on the transverse-slide to move the latter. A shrouding-device 25 is adjustable by hand to vary the effectiveness of the ratchetpawl and adjust the feed-step. The ratchetwheel may also be turned by hand. The ratchet-teeth extend only part way around the periphery of the wheel so that the feed-action stops after a predetermined amount of feed. A second form of automatic-feed-device comprises a plunger 34, Fig. 5, slidable against a compression spring 36 in a bore arranged tangentially to a ratchet-wheel 32 secured to the transverse-slide 7. The plunger carries a pawl 35 which moves the ratchet-wheel on outward movement of the plunger by the spring. The latter is compressed by the plunger striking an adjustable-stop 38 on the bed when the carriage 6 reaches the end of its forwardtraverse. The back of the ratchet-wheel is provided with a helical cam which engages a stop on the carriage to effect the transversefeed. In an alternative embodiment of the invention, a similar transverse-feed-device to that last described is used, but the longitudinal traverse is effected by a screw 41, Fig. 8, engaging a roller 43 on a lever 44. The latter is moved automatically to disengage at the end of the braking-stroke, by a trip-arrangement, and the carriage is returned by a spring 13. The return is cushioned by a plunger 59, attached to the carriage, entering a cylinder 58 secured to the base and having an adjustable airescape valve 61.