Patent GB-500486-A (GB)
Title: Automatic reverse for screw tapping devices in machine tools
IPC: B23B39/12
Filed: 1937-08-09
Abstract: 500,486. Drilling and tapping machines. CINCINNATI BICKFORD TOOL CO. Aug. 9, 1937, No. 21890. Convention date, March 9, [Class 83 (iii)] In a screw-tapping machine wherein the tool spindle is selectively rotatable in opposite directions by a normally idle reversible prime mover, a manually operable control member is movable from neutral to alternative effective positions for starting the prime mover in the desired direction and automatic means temporarily override the manual control to maintain the drive in the initial direction, whilst the manual control is returned to neutral, until the drive is automatically reversed. As applied to a radial arm drilling machine a base 11 carries a pillar 12 on which a sleeve 13 isrotatably mounted and the arm 14 is vertically adjusted on the sleeve 13. A drill head 15 is slidable along the arm and is partly balanced by an electric motor 21 which drives the spindle 16 through an arm shaft 22 and change speed gearing in the head. The quill 29, Figs. 3 and 4, is fed by a change gear train driven from the spindle and connected to a shaft 25 carrying a worm driving a worm wheel 26 loose on a shaft 27 provided with a pinion 28 engaging a rack on the quill. A head 30 on the shaft 27 has hand feed levers 31 pivoted thereto at 33 which carry toothed segments 38 engaging teeth on a bar 37 slidable through the shaft 27. A cam on the bar engages radial pins 36 which act on levers 34 pivoted to the head 30 and provided with toothed portions engageable with teeth on the worm wheel 26, the levers being normally held in the disengaged position by springs. Thus oscillaticn of the levers about the pivots 33 engages or disengages the power feed. The power feed may he stopped at any predetermined point of a drilling operation by means of a normally stationary dog 39 on an angularly adjustable ring 39a which lies in the path of a projection 40 on one of the levers 31 when the latter are in position to engage the clutch. The clutch may also be disengaged at each end of the travel of the quill, and for this purpose a bevel gear 41 on the pinion shaft 27 drives a bevel gear 42 loose on a shaft 43. A gear 44 on the bevel 42 rotates, through back gears 45, Fig. 4, a gear 48 loose on the bevel 42 and carrying a cam 49, Fig. 3, adapted to actuate a plunger 50 which acts on the cam bar 37 through a lever 51. The cam 49 makes slightly less than one revolution during the full travel, of the quill. The pinion 28 may be rotated a small distance. further by hand at either limit of travel, until the cam 49 engages a positive stop 50a. The shaft 46, Fig. 4, to which the back gears 45 are secured, may also be rotated by means of a hand lever 52 and a releasable catch 55 when a slow powerful hand feed for the tool spindle is required. The shaft 46 may also be rotated by a handle 53 having a lost-motion connection therewith provided by a roller 58 thereon engaging a short helical slot 57 in the shaft, the axial motion of the handle on the shaft being utilized to actuate forward and reverse switches for the motor 21 driving the spindle. A handle 54 is rigidly secured to the shaft 46 for feeding the quill without effecting rotation of the spindle. A spring detent 53a determines the forward, reverse and neutral positions of the handle 53. For tapping, rotation of the handle 53 first engages the switch for rotating the, tap in a forward direction, and when the roller 58 meets the end of the slot 57 further rotation of the handle feeds the tap to the work to start the tapping operation. The tap then feeds itself and on attaining the required depth, reversal of the handle 53 reverses the direction of rotation of the tap for backing out. To produce automatic reversal when the tap has reached the required depth, a rack bar 71, Fig. 6, is engaged by a pinion 70 on the shaft 46 so as to be moved in synchronism with the tap spindle 16. A block 74 is adjustably secured to the bar 71 and carries a spring plunger 78 adapted to engage a lever 79 as the bar is fed downwards, the lever 79 being attached to a lever 81, Fig. 10, which actuates switches for reversing the motor 21. An adjustable pointer 76 on the block 74 cooperates with a scale 77 fixed to the tool head, the arrangement being such that the motor is reversed when the pointer reaches the zero of the scale. Thus the pointer may be set relatively to the bar 71 at the required depth of tapping indicated on the scale, when the tap is engaging the upper surface of the work. The switches a, b, Fig. 10, which control solenoids F, R for operating the master switch M to drive the motor 21 in the forward and reverse directions respectively, are actuated by a block 59 connected to the rotatable and axially movable handle 53 by a yoke. Spring plungers 61, 62 on the block engage a lever 63 which actuates the switches, the positions shown in Fig. 10 producing a dead circuit 3, 6, 5, 4, 3 from the supply 1, so that the motor is at rest. Rotation of handle 53 to start a tapping operation throws switch a to establish a circuit 3, 8 through solenoid F for forward rotation of the tap, and when the plunger 78 engages the lever 79, a switch c is thrown to remove control of solenoid F from switch a, the circuit then being 3, 4, switch h, 5, 7, 8 and solenoid F, the switch g being closed by being mechanically connected to the master switch M. Further motion of the tap spindle and plunger 78 rocks the levers 79, 81 to engage a spring plunger 85 and move the lever 63, thus opening switch a and closing switch b. This energizes the reverse solenoid R and simultaneously breaks the circuit through switch b to switch c, thus cutting ont solenoid F. After the tap has hacked oiit. it may be raised and its rotation stopped by rotation of the handle 53. When setting up the machine the switch g is open to break the circuit to switch c so that the tap spindle may be moved downwards without allowing the plunger 78 to start rotation of the spindle. For drilling, the motor may be controlled through switches d, e, operated by a hand lever 91 on the tool head, the switches e, a, b, c, d then being all in series. A switch r, l controls the motor for raising and lowering the arm 14 and is actuated by a hand lever 20 which also effects the clamping of the arm, as described in Specification 500,616. A switch s prevents starting of the motor by the tool-control handles 53, 91 when the arm is unlocked.