Continuous drive for rotating with a constant cutting speed on lathes with selectable cutting speed

摘要

858,710. Lathe details. COHEN 600 GROUP Ltd., G. Nov. 12, 1957, No. 35226/57. Class 83 (3). [Also in Group XXXIV] A lathe or other machine tool is provided with an infinitely-variable friction drive which is coupled to the cross-slide feed to give constant cutting speed during facing operations. The friction drive may be of a known type or may be as described in Specification 858,708. In an embodiment of the invention, a friction drive has the speed-ratio adjusted by rotating a plate 31, Fig. 1, having curved depressions corresponding to the tiltable spherical driving elements 5, and curved slots 15 into which fit the ends 14 of the spindles on which the driving elements rotate. The plate 31 is rotated by a central spindle 32, which is coupled to a torsion bar 58, Fig. 3. When the friction-drive device is stationary there is high resistance to adjustment, so the torsion bar stores energy equivalent to the amount of adjustment required, which is taken up by the latter when it starts rotation. The cross-slide 67 carried by a saddle 68, has a rack 72 which moves a gear 70 on facing movement. A shaft 71 has a slidable key connection to the gear 70, and thus rotates, through change wheels 73, 74, a gear 78 rotatable on the end of the torsion-bar 58. The gear 78 is fixed to, or integral with, a notched disc 63, and an arm 55 fixed to the torsion bar carries a spring-pressed plunger which engages the notched disc. Motion is thus transmitted from the cross-slide to the torsion-bar. A handle 57 connected to the spring-pressed plunger moves through a gate or slot in a fixed plate 59 between stop limits according to the amount of adjustment of the plate 31. The handle 57 may, therefore, be pre-set to give a desired starting speed for the drive, which setting is taken up when the drive commences. When operations other than facing at constant cutting speed are to be carried out, one of the change-speed wheels 73, 74 is removed and a locking-pin 77 inserted to maintain the wheel 78 stationary. The notched member 63 is thus also locked and may be used to position the torsion-bar by the handle 57. An arrangement of notched disc 82 and locking plunger 81 may be employed at the end of the torsion-bar adjacent the friction drive, so that the latter may be locked to give a particular drive-ratio, and the other end of the torsion-bar pre-selected for a new drive-ratio. When the new ratio is required to operate, the plunger 81 is withdrawn and locked by a knob 85. Specifications 618,774 and 858,709 also are referred to.