Fig. 1789.
[Fig. 1789] represents a drill crank which receives the drill at a, and is threaded at b to receive a feed screw c, which is pointed at d; at e is a loose tube or sleeve that prevents the crank from rubbing in the operator’s hands when it is revolved.
Fig. 1790.
To use such a drill crank a frame a, [Fig. 1790], is employed, being held in a vice and having at t a table whereon the work w may be rested. The feed is put on by unscrewing the screw s in this figure against the upper jaws of a; holes of about half inch and less in diameter may be drilled with this device.
Fig. 1791.
A very old but a very excellent device for hand drilling when no drilling machine is at hand is the drilling frame shown in [Fig. 1791], which consists of two upright posts a, and two b, placed side by side with space enough between them to receive and guide the fulcrum lever and the lifting lever. The fulcrum lever is pivoted at c, and has an iron plate at e, and suspends a weight at its end which serves to put on the feed. The lifting lever is pivoted at d, and at f hooks on to the fulcrum lever. At its other end is a rope and eye g, and it is obvious that the effect of the weight upon the fulcrum lever is offset by any pressure applied to g, so that by applying the operator’s foot at g the weight of drill feed may be regulated to suit the size of hole and strength of drill being used. The work is rested on a bench, and a drill crank or other device such as a ratchet brace may be used to drive the drill. This drill frame is capable of drilling holes up to about two inches in diameter, but it possesses the fault that the upper end of the brace or drilling device moves as the drill passes into the work in an arc h of a circle, of which the pin c is the centre. The posts a are provided with numerous holes for the pin c, so that the fulcrum lever may be raised or lowered at that end to suit the height of the work above the work bench. Another objection to this device is, it takes up a good deal of shop room.