GB600672A - Improvements in thread cutting devices in lathes - Google Patents

Abstract

600,672. Lathes. SOC. CRI-DAN. June 12, 1945, No. 14915. Convention date, April 7, 1941. [Class 83 (iii)] A screw-cutting device for lathes, in which the tool is automatically given a transverse advance after each stroke, comprises a cam with an increasing profile driven progressively by means of a pawl and ratchet wheel, the pawl being rendered inoperative after the final stroke by an abutment arranged coaxially with the cam and the ratchet wheel, the cam and the abutment being angularly adjustable relative to the ratchet wheel. A cutting tool 2 operating on work 3 is carried by a cross slide 1 traversed longitudinally by a cam 6, Fig. 2, engaging a roller 8 on a spring-returned rod 5 secured to the longitudinal carriage. The cross-slide is pulled in a direction away from the work by a spring 4 which maintains a button 14 against a flat plate 15 provided on a rockable member 20. The button 14 is carried by an axially adjustable screw 12 in an angularly adjustable holder 11 rocked by a screw and rack segment to raise or lower the button relative to the plate, thus adjusting the amplitude of motion of the tool received from the plate movement. The rockable member 20 is pivoted at 21 to the arm of a bell-crank lever 25, 26, pivoted at 24. The other arm 26 of this lever receives rocking motion from a cam 28, driven in timed relation with the work, to withdraw the tool from cut at the end of a cutting stroke and re-apply it at each new cutting stroke. Additional stepped feed movements of decreasing amount are applied at each new cut to the rockable member 20 by a cam 23 also arranged on the axis 24 and contacting a roller 22 on the rockable member. The cam is integral with a worm wheel 44, Fig. 5, and arranged on the same axis are, a ratchet wheel 33 integral with a member 29, and a stop member 46 integral with a worm wheel 45. The worm wheels are engaged by adjustable screws 40, 41 rotatable in lugs carried by the member 29 thus rendering cam, ratchet wheel, and stop member 46, relatively angularly adjustable. A spiral spring 30 forces the arm 29 against a stop 31, Fig. 1, at the start of a cutting operation and a pawl 34 carried by the lever 26 rotates the ratchet wheel and cam step by step at each cutting stroke until the stop member 46 strikes a lever 47 which releases the shaped end 52 of a bellcrank lever 53 pivoted at 54 and adapted to be pulled clockwise by a spring 55. The lever 53 strikes the ends 56, 57 of the ratchet pawls to release the ratchet and member 29 which are thus returned to the starting position. The lever 53 also stops the machine through mechanism not described. The operative face of the plate 15 may be inclined to the axis of the work for cutting a tapered thread.