305,978. National Automatic Tool Co., (Assignees of Galloway, R. M.). Feb. 13, 1928, [Convention date] Drilling-machines ; tapping.-A metal-cutting machine tool comprises a frame 11 carrying a rotary work table 12 around which are located a number of self contained detachable units such a.s drilling, tapping and milling units each unit being provided with its own driving motor and controlling mechanism. The tapping unit may be particularly adapted for simultaneously tapping a number of spaced holes in an engine crank case. The frame carries a chip pan 13 with a screen 14 for the coolant.. The table 12 carries brackets 17 which may support the work and may provide bearings 19 to receive guides 20 on the drill unit 15. The latter comprises an electric motor 26 driving drill spindles 27 and a reciprocating slide 22 actuated hydraulically from a pump 25. Instead of arranging, the tapping unit 16 as shown in Fig. 1 the units may be arranged at any required angle to the work table. A tapping unit for engine crank cases is shown in Fig. 2. The gear box 30 carries spindles 31 splined to shafts 37 which carry lead screws 35 engaging in nuts 36 mounted in a front plate 33 for feeding the taps 32. One or more interchangeable driving units 38 may be employed each comprising a motor 50 driving through spur gearing a shaft 56, Figs. 6 and 7. In some cases the motors 50 may be replaced by a single driving motor geared to both shafts 56. The shaft 56 carries gears 69, 70 arranged to impart opposite rotations to gears 73, 74 which are loosely mounted on a shaft 39 and are clutched thereto by a sliding clutch member 76. The shafts 39 are geared to the various tap spindles by means of spur gearing as shown in Fig. 3. A left-hand screwed portion 77 of the shaft 39 actuates a block 78 fitted with a lug 93 which moves between spaced abutments 94, 95 on a sliding block 96 which is connected by a lever 97 with a lever 99a pivoted on a shaft 80. A projection on the lever 99a engages between the abutments 101, 102 on the forked portion of a member 86 which has a gear segment engaging teeth on the reversing clutch member 88. A spring plunger 83 coacts with a projection 82 to provide a load-andfire device for quick reversal. The shaft 80 carries a lever 81, the end 109 of which is normally latched by a pivoted lever 105 pressed up by a spring plunger 110 and disengaged by means of a fluid pressure cylinder 111. In operation, to initiate a tapping cycle, fluid is admitted to release the lever 105 whereupon the clutch is snapped to the left and the tap is driven on its forward stroke. This causes the nut 78 to move to the left until the lug 93 engages the abutment 95, thus actuating the lever mechanism to change over the clutch and reverse the drive of the taps. The backward movement continues until the projection 93 engages the opposite abutment 94 and again shifts the clutch and if there is no pressure in the cylinder 111 the lever 81 is held up by its latch to hold the clutch in a neutral position. If, however, the pressure, in the cylinder 111 is maintained the action is continuous. An emergency trip mechanism consisting of a pneumatic cylinder 114 provided with a plunger 118 coacting with the slide 96 may be brought into operation to reverse the taps at any required time. The control valve 120 may be of the four-way type and operation of the handle 121 may be arranged selectively to admit air either through a pipe 117 to the emergency trip cylinder or through a pipe 112 to the latch trip mechanism cylinder. Where a number of units 38 are employed the pipes 117 and 112 may be respectively connected to all the emergency and latch trip cylinders. Specification 309,567 is referred to.