| 摘要 |
335,713. Cincinnati Bickford Tool Co. March 12, 1929, [Convention date]. Drilling-machines. - A clamping-mechanism for a radial arm drilling-machine has a clamp element operated by a reversible overload electric motor, the circuit to which includes a manually operable, self-opening switch, the motor being adapted to remain under the influence of the current without overheating until the operator allows the switch to open and means being provided for stalling the motor when the clamp is tightened or untightened. The clamp comprises a sleeve 1, Fig. 1, split at 2 so as to be capable of contraction on a pillar 5. Lugs 6, at one side of the split 2 rotatably support a shaft 7, provided with an eccentric 29 whose strap 10 carries a bolt 11 passing through a lug 8<1> on the other side of the split 2. Rotation of the shaft 7 closes the clamp through the head 12 of the bolt 11, a sleeve 13, and a thrust bearing 14. Bolts 15 adjustably attached to the lugs 6 pass through lugs 8 and limit the opening of the clamp. The upper end of the shaft 7 carries a worm sector 18, Figs. 1 and 2, engaged by a worm 17 on the shaft of a motor M. In operation, a press switch is depressed against the action of a spring to close the circuit to the motor, whereupon, the shaft 7 is rotated and the clamp closed. When the eccentric 9 is on or past its dead centre a lug 21 on the sector 18 engages a stop 19 to prevent further rotation of the shaft 7 and cause the motor to stall, the motor being so constructed that it will not suffer damage through being stalled for about three minutes and the strength of the spring on the press switch being so arranged that the operator will not be able to depress the switch continuously for this time. A second similar switch is provided for rotating the motor M in the opposite direction, a lug 23 coming into contact with a stop 22 when the clamp is open. Alternatively, the stop 22 may be replaced by a spring stop. In a further alternative, the worm 17, Fig. 6, meshes with a complete worm-wheel 25 provided with recesses b engaged by spring-pressed balls 27 located in radial recesses in a disc B secured to the shaft 7. The recesses b are steeper in one direction of rotation than in the other so that the closing torque applied to the clamp will always be less than the opening torque, thus ensuring that the motor will never fail to open the clamp. The pressure of the springs 26 on the balls 27 may be adjusted by a sleeve P whose conical end 30 is pressed by a nut 33 - against balls 29 forming abutments for the springs. An arm 35 on the shaft 7 comes into contact with a fixed stop on the casing 20 in the clamping direction and against a spring stop 24 in the unclamping direction, the motor then being allowed to run continuously whilst the press switch is depressed due to slipping of the balls 27. A hand lever 16, Fig. 1, keyed to the bolt 11 provides for actuating the clamp by hand. |
