Turning and Boring / A specialized treatise for machinists, students in the industrial and engineering schools, and apprentices, on turning and boring methods, including modern practice with engine lathes, turret lathes, vertical and horizontal boring machines

by Franklin Day Jones

Fig. 40. Drilling in the Lathe

Drilling and Reaming.—When a hole is to be bored from the solid, it is necessary to drill a hole before a boring tool can be used. One method of drilling in the lathe is to insert an ordinary twist drill in a holder or socket S, [Fig. 40], which is inserted in the tailstock spindle in place of the center. The drill is then fed through the work by turning the handle n and feeding the spindle outward as shown by the arrow. Before beginning to drill, it is well to turn a conical spot or center for the drill point so the latter will start true. This is often done by using a special tool having a point like a flat drill. This tool is clamped in the toolpost with the point at the same height as the lathe centers. It is then fed against the center of the work and a conical center is turned. If the drill were not given this true starting point, it probably would enter the work more or less off center. Drills can also be started without turning a center by bringing the square end or butt of a tool-shank held in the toolpost in contact with the drill near the cutting end. If the point starts off center, thus causing the drill to wobble, the stationary tool-shank will gradually force or bump it over to the center.

Fig. 41. Flat Drill and Holder

Small holes are often finished in the lathe by drilling and reaming without the use of a boring tool. The form of drill that is used quite extensively for drilling cored holes in castings is shown in [Fig. 41], at A. This drill is flat and the right end has a large center hole for receiving the center of the tailstock. To prevent the drill from turning, a holder B, having a slot s in its end through which the drill passes, is clamped in the toolpost, as at C. This slot should be set central with the lathe centers, and the drill, when being started, should be held tightly in the slot by turning or twisting it with a wrench as indicated in the end view at D; this steadies the drill and causes it to start fairly true even though the cored hole runs out considerably.