Boring tools which are designed for use in the engine lathe are generally of a very simple kind, adapted only to light cutting and seldom used for more than one or two pieces of work of the same size at the same time. Several varieties are to be found in the average tool-room, although forged tools will be noted in greater numbers than any of the others. Tools of this kind of almost every conceivable shape and size, from a small round "hook tool" for cutting an inside recess, to a large bar of tool steel bent over at the end for boring some long pieces of work, will be found in abundance. There are square bars and round bars with inserted tools, and, in addition to these, each toolmaker has a special boring tool of his own make which he uses for jig work. These special tools occasionally show considerable ingenuity in their construction, and are usually made in such a way that very fine adjustments can be attained.

The upper part of Fig. 1 shows a piece of work A held by the outside in chuck jaws, the machine on which the work is to be done being an engine lathe. A plain forged ,tool B is held in the toolpost G on the cross-slide of the lathe. This type of tool is the simplest of all tools used for boring and consists of a rectangular piece of tool steel of suitable size to fit the toolpost. The tool is drawn out and bent over at the cutting end by the blacksmith and is then ground to a cutting edge by the workman using it. Hundreds of tools of this variety can be found in every machine shop and factory in this country. They are suitable only for light cutting and there is a tendency toward "chatter" even when the cut is light; this is due partly to the shape of the cutting end and partly to the overhang of the entire tool. It will be found that less chatter will result if a slight land or flat is stoned on the tool immediately below the cutting edge. The tool should also be set slightly above the center. For casting work where scale is encountered, there is a decided tendency for the tool to ride up on the scale and ruin very rapidly if it is ground as shown at B. The enlarged view M shows another method of grinding which is useful in cases of this sort. It will be noted that there is a slight back taper to the end of the tool and this assists in preventing any riding up on the scale, as its tendency is to make the cutting point draw in slightly and thus keep under the scale. Care must be taken not to make the angle too great - 5 degrees is ample, and much less than this can be used if desired.

Fig. 1. (Upper View) Forged Type of Boring Tool; (Lower View) Boring Tool with Inserted Cutter.

Fig. 2. Two Types of Adjustable Boring Tools for Tool-room Work.

The lower part of Fig. 1 shows the same piece of work D with another type of boring tool in action. A cast-iron body K is held down on the cross-slide of the lathe by means of the three bolts J. A steel bar G is longitudinally adjustable in the cylindrical portion of the holder and is clamped in position by means of the binder screw H. A round cutting tool E is held in place by the taper pin F, in a manner familiar to all. A holder of this type will be found a very useful adjunct to any toolroom, and is adaptable to a variety of conditions. A series of bushings can be made to take different diameters of round stock, and tools may be quickly made to suit almost any case. Obviously, adjustment for diameters is made by the cross-slide. Rigidity and adaptability are points in favor of this device.