GB472400A - Improvements in or relating to screw-cutting or tapping machines - Google Patents

Abstract

472,400. Screwing; tapping. HERRMANN, R. March 20, 1936, No. 8335. [Class 83 (iii)] In a machine for screwing or tapping the tool-holding spindle is driven by coaxial splined members, the lower ends of the splines on the outer member having lateral enlargements forming shoulders in the splines against which the ends of the splines in the inner member lie so as to provide a positive axial feed during screwing whilst on reversal of rotation of the drive, the inner member rides off the shoulders and thereby floats axially relatively to the outer member so that the end threads of the work will not be damaged when the tool spindle is drawn away from the work by a spring. The tap &c. spindle 21 has a splined end 51 engaging grooves 50 in a hollow spindle 3 which is journalled at 20 in a quill 2. The spindle 3 is secured to a shaft 17 splined within a gear 11 which is rotated by a reversible electric motor 7. The lower ends of the grooves 50 are stepped at 53, Fig. 8, so that the splines 51 will take the positions shown in this Figure when the spindle 3 is rotated in the tapping direction. On feeding the tap against the work by means of a pinion 31 driven from the motor 7 and engaging the quill 2, the ends of the splines 51 are pushed against the steps 53, taking up the clearance L, and the tap is fed into the work. The spindle 3 is held axially in the position shown in Fig. 8, by means of a light spring 55 within the spindle 3, and a spring 58 abutting on a cap 59 attached to the spindle and pressing a flanged ring 60 against a shoulder 56 on the spindle 21, the ring 60 then abutting the lower end of the spindle 3. On reversal of the drive the splines 51 ride off the steps 53 and are free to enter the grooves 50, whereby the tap is relieved of axial pressure by the spindle and will not damage the end threads of the work when the quill 2 is moved upwardly by a spring 28 engaging a head 27 on a rod 25 attached at 24 to the quill. For tapping small or delicate threads the ring 60 may be reversed, with the spigot portion entering a recess 61 in the spindle 3, whereby the spring 58 will maintain the spindle 21 in an elevated position with the splines 51 lying in the grooves 50 above the level of the steps 53 and the tap will not be subjected to axial pressure by the spindle 3, except through the spring 55. Tap-spindle and screwing feeds; yielding drive.-The feed pinion 31 is driven from a shaft 34 through a free-wheel clutch which allows the quill 2 to be raised by the spring 28 onlv, and the shaft 34 is driven from the shaft 17 by spur gearing 43, worm gearing 38 and change gears 36, Fig. 3. The shaft 34 carries a flange 62 provided with recesses having tangential bases and containing rollers 64 engaging a drum 66 so as to rotate it in one direction only. Stops 67, 68, adjustably attached to the drum, actuate a switch 47, Fig. 1, and also a reversing clutch, if required, at the end of each downward and upward stroke to reverse the direction of rotation of the motor 7 by means of contacts 48, 49. The hollow shaft 33 carrying the pinion 31 is driven from the drum 66 through an overload clutch comprising recessed plates 71, 72 attached to the shaft and drum respectively and. balls 74 supported by a cage 75, the plate 72 being attached to the drum by pins 73. The limiting torque of the clutch is determined by a spring 78 abutting on a plate 80 which is adjustable by screws 81, and the axial thrust is taken by a ball bearing 82 and a cap 85 held to the drum 66 by a spring ring 86. In a modification, the driving shaft 101, Fig. 19, is splined at 102 within a sleeve 95 slidable in the hollow spindle 100 and normally pressed downwards against a shoulder 97 by a spring 96 which is capable of supplying full axial feed pressure. The sleeve 95 is splined to the tap spindle 21 by means of the same stepped grooves 50 as those shown in Fig. 4. When the tap engages the bottom of a blind hole or a piece of undrilled work &c., the tap spindle and sleeve 95 move upwardly relatively to the spindle 100 until the rotation has been reversed, thus removing the necessity for a yielding clutch in the feed train. Reversing mechanism.-When the tap engages the end of a blind hole the clutch 71, 72 slips and a plate 79 attached to the pins 73 is pushed back by the balls 74 so as to cause ratchet teeth 93 thereon to engage teeth on a sleeve 87 splined at 88 to the shaft 34 whereby the drum will be rotated from this shaft to cause one of the stops 67 to reverse the rotation of the motor 7. The clutch 71, 72 then reengages and the clutch 79 is disengaged.