Patent GB-810179-A (GB)
Title: Improvements in or relating to thread-cutting machines, and more particularly thread-grinding machines
IPC: B24B19/02
Filed: 1956-06-01
Abstract: 810,179. Screw - cutting. LINDNER G.m.b.H., H. June 1, 1956 [June 2, 1955], No. 17078/56. Class 83 (3). [Also in Groups XXIII and XXXVII] A screw-thread cutting-machine, especially a thread-grinding machine, of the kind including a work-carriage moved on the working stroke and on the rapid-return stroke by a a lead-screw driven from a rotatable work-spindle through interchangeable gears which determine the thread pitch, is characterized in that the rates of rotation of the work-spindle during the working and return strokes respectively are controlled by two independent regulators brought alternately into operation so as to determine the speeds of a motor driving the work-spindle during these strokes, the return-stroke regulator possessing operative positions which correspond to the pitch of the thread, and impart to the work-spindle during the return-stroke a rate o rotation which, for all transmission ratios of the interchangeable gears corresponding to the thread pitch, imparts to the lead-screw an approximately constant rate of rotation, whereby an approximately constant rate-of-return is imparted to the work-carriage during the return stroke, independently of the rate of rotation of the work spindle and lead-screw for the working stroke. The lead-screw 2 mounted in the work-carriage 1 meshes with a nut 4 carried by the machine-frame 3 and is driven from the work-spindle 7 by spur-gears 20. 21 and interchangeable gear-wheels 8 which determine the pitch of the thread. The work-spindle 7 is driven by a variable-speed motor 5, gearing 6 and a two-speed gear; when the electromagnetic clutch 12 is engaged a shaft 17 is driven through worm 10 and worm-wheel 11 at slow speed, and when electromagnetic clutch 16 is engaged the shaft 17 is driven through bevelgears 13 and spur-gears 14, 15 at fast speed. The shaft 17 drives the work-spindle 7 through worm-gear 18, 19. A control panel 23 on the machine frame carries a rotary control-member 24 for a regulator 25 for determining the motor speed during the working stroke, a rotary control-member 26 for a regulator 27 for determining the motor speed during rapid return, a tachometer 28 indicating the rate of rotation of the work-spindle, and press-button switches 29, 30,31. A centrifugal switch 32 is driven by the lead-screw 2 through speed-increasing gearing. The control member 26 for the rapid-returnstroke regulator 27 has a scale 34 indicating the pitches obtainable by interchanging the gearwheels 8, and also showing the corresponding work-spindle speed to give a substantially constant speed to the lead-screw during rapidreturn. The regulators 25, 27 are connected in parallel in the circuit of the field-winding 62 of the D.C. motor 5. For the working stroke, the button 29 is depressed, closing switch 29<SP>1</SP> to energize contactor 63; switch 63<SP>1</SP> opens to deenergize contacts 64; contact 63<SP>2</SP> closes to establish a holding-circuit for contactor 63; contact 63<SP>3</SP> opens to disconnect regulator 27 so that the motor speed is determined solely by the regulator and contacts 634, 63<SP>5</SP>, 63<SP>6</SP> close to switch on the motor for forward rotation. Clutch 12 is engaged by contactor 63. Contactor 63 can be de-energized by depressing a button 31. For the rapid-return stroke, the button 30 is depressed, closing switch 302 to energize contactor 64; switch 64<SP>1</SP> opens to deenergize contactor 63; contact 64<SP>2</SP> closes to establish a holding circuit for contactor 64; contact 643 opens to disconnect regulator 25 so that the motor speed is determined solely by the regulator 27; contacts 644, 64<SP>5</SP>, 64<SP>6</SP> close to switch on the motor for reverse rotation. Clutch 16 is engaged by contactor 64. If the control member 26 is set incorrectly to give too high a speed to the lead-screw during the rapidreturn-stroke, the centrifugal switch 32 opens to stop the motor.