A breast-plate for drilling is made of thin sheet iron or steel, and is bent to a curved form that it may fit the operator's hand or chest. If a large amount of drilling is to be performed by such means, two holes may be made into the plate to contain ends of strings by which the tool may be tied to the workman's waist. The bearing portion of the plate, which sustains all the friction of the conical drill-pivot, consists of a plate of steel about a quarter of an inch thick; this is smoothly recessed in five or six places, and a couple of holes are bored by which to rivet or screw it to the thin plate. After being properly smoothed, the bearing-plate is hardened, but not tempered ; it is next attached to its breast-plate, and the tool is then ready for use. A breast-plate made by such means is shown by Fig. 475.

Drill-Bows

The cheapest sort of drill-bow is that which is made of an ash or hazel stick, which has a thin ferrule tightly fitted to each end, and a couple of holes bored through to contain the ends of the thong or string by which the drill's pulley is rotated. A superior sort of drill-bow is made of a thin piece of sheet steel, in which a hole is bored at each end to hold two hooks for attaching the thong; or the thong may be fastened to the steel without any hook. The thong or band of the drill-bow is an engineers ordinary band-lace, and should not be twisted, but applied flat to the pulley and occasionally chalked.