Fig. 1794.
[Figs. 1793] and [1794] represent a self-feeding ratchet brace for hand drilling in which the feed is obtained as follows: The inside or feed sleeve b, which screws upon the drill spindle, is fitted with a friction or outer sleeve a, in the head of which is secured a steel chisel-shaped pin c, the lower end of which is pointed and rests upon a hardened steel bearing d, fixed in the head of the inner sleeve b. This sleeve, with its bearing d, revolves upon the point of the pin c, and within the friction sleeve a. Having thus described its construction, we will now describe the operation of the self-feeding device. The head of the pin c being chisel-shaped, prevents the pin and the outer sleeve a from revolving. If the thumb or friction screw f is unscrewed, it will permit the inner sleeve b to rotate freely upon the bearing of pin c, and within the friction sleeve a. As the screw f is tightened, the friction upon the inner sleeve b is increased, causing it to remain stationary, and consequently causing the screw on the drill spindle to feed the drill until the friction on the drill becomes greater than the friction on the sleeve b. This then commences to rotate again within the outer sleeve a, and continues until the chip which the drill has commenced to cut is finished, when the same operation is repeated, thus giving a continuous feed, capable of being instantly adjusted to feed fast or slow as desired, by tightening or loosening the friction screw f, thereby causing a greater or less friction upon the inside or feed sleeve b.
Fig. 1795.
To afford a fulcrum or point of resistance for the chisel-piece c, or the pointed centre used in the common forms of ratchet brace feed screws, various supporting arms, or stands are employed. Thus [Fig. 1795][30] represents a boiler shell a, to which is attached an angle frame or knee b, carrying the angle piece c (which may be adjusted for vertical height on b by means of the bolt shown) affording a fulcrum for the feed sleeve d. This sleeve is sometimes made hexagonal on its outside to receive a wrench or to be held by the hand when feeding, or it may have holes near its centre end to receive a small pin or piece of wire; e is a chain to pass around the boiler to secure b to it, which is done by means of the device at f.
[30] From The American Machinist.
For many purposes a simple stand having an upright cylindrical bar carrying an arm that may be set at any height and set to its required position on the bar by a set-screw is sufficient, the base of the stand being secured to the work by a clamp or other convenient device.