Drill bit

“ The starters were a foot long, each succeeding drill five or six inches longer than the preceding one and slightly narrower at the bit, so that it would follow in the hole. Seven or eight drills made a set, the longest four or five feet. Carefully he wrought, and watched with anxious eye as he plunged the hissing points into the water and, holding them up, saw the temper draw steel-blue and white-specked to the edge. For if a piece broke from one of the bits, no more could be done in that hole. The broken particles of steel would be ground into the rock. ”

“ In single-hand drilling, the miner wields the hammer with one hand, and with the other holds the drill or “bit,” rotating it slightly after every blow in order to keep the hole round and prevent the drill from sticking fast; in double-hand work, one man strikes, while the other holds and rotates the drill. For large and deep holes, two hammermen are sometimes employed.
A miner’s drill is a steel bar, occasionally round but generally of octagonal cross-section, one end of which is forged out to a cutting edge (fig. 1) . ”

“ DRILLING MACHINES
Everybody knows that oil wells and derricks go together. The tall derrick towers are needed to hoist drilling equipment in and out of the hole.
When men start to drill a well, they fasten a cutting tool, called a bit, to a piece of pipe which hangs upright{70} in the derrick. Machinery turns the whole thing round and round, so that the bit grinds down into the earth. When one length of pipe, called a joint, has almost disappeared into the hole, men screw another joint onto the top of it. Now the engine turns the double-length pipe, and the bit digs down deeper. ”

“ This is useful for making small holes when there is danger of the wood splitting, however when once this drill is used, the worker never again feels inclined to use a bradawl or any other kind of boring tool. A quite useful and efficient drill can be bought for sixpence. Care must be taken that the drill bits or drill points do not break, for being quite slender and made of tempered steel they are rather fragile. A set of twelve drill points in assorted sizes in a metal case may be bought for sixpence. (For hints on the use of drill, see under fret-saw.) ”

“ In cases of extreme hardness two drills may with advantage be used intermittently upon the same hole; one of these should have its cutting edges ground at a more acute angle one to the other than is the case with the other drill, thus the cutting edge will be lessened in length while the drill will retain the strength due to [I-445] its diameter, so that a maximum of pressure may be placed upon it. When one drill has cut deep enough to bring its full length of cutting edge into action, it may be removed and the other drill employed, and so on. ”

“ The large charges in deep holes break the walls very irregularly; misfires cause more delay; timbering is more difficult in the face of heavy blasting charges; and the larger amount of spoil broken at one time delays renewed drilling, and altogether the advantages seem to lie with hand-drilling in shafts of large horizontal section.
The rapid development of special drills for particular conditions has eliminated the advantage of hand-work in many situations during the past ten years, and the invention of the hammer type of drill bids fair to render hand-drilling a thing of the past. ”

“ In determining the amount of clearance, therefore, we are compelled to make it sufficient for the point of the drill, and this under this system of grinding is excessive for the outer diameter of the drill, causing it to dull quickly, it being borne in mind that as the outer corner of the cutting edge of a drill describes the largest circle of any point of the cutting edge it obviously performs the most cutting duty in removing metal, and furthermore revolves at the highest rate of cutting speed, both of which cause it to dull the most rapidly. ”

“ Fig. 15 is a side tool for squaring the ends of shafts; Figs. 16, 17, 18, and 19 represent tools for brass, Fig. 16 is a round-nosed tool for brass, Fig. 17 a V shaped tool, Fig. 18 a screw thread tool, and Fig. 19 a side tool. In boring, whether the object is cored or not, it is desirable, where the hole is not too large, to take out the first cut with a drill. The drill for the purpose is shown in Fig. 20, the drill holder in Fig. 21, and the manner of using in Fig 22. The drill holder, B, is held by a mortised post placed in the rest support. ”

“ The drill must be tried for running true at each end of the cylindrical body of the drill, which, being true with the square shank, may be taken as the standard of truth in grinding the drill, so that supposing the hole in the driving spindle to be true and the drill shank to be properly fitted, the drill will run true whichever way inserted. If the body of the drill runs out of true it will cause a great deal of friction by rubbing and forcing the cuttings against the sides of holes, especially if the clearance be small or the hole a deep one. ”

“ In using twist drills, and these are the only satisfactory kind for metal work, be mighty careful not to press too hard on the drill stock and don’t try to crowd the drill into cutting faster than it will cut at the speed with which it is turning. In drilling iron keep plenty of oil on the drill point.
(7) You can measure much more accurately with a steel rule than you can with a wood rule and whereas measurements in cabinet work down to 1⁄16 inch are close enough, for metal work it should not be more than 1⁄32nd of an inch, and for machine work make your measurements to 1⁄64th of an inch. ”

“ We are now ready to temper our drill, and we must exercise a little care that the steel is not burnt and that the drill is not bent or warped when hardening. The flame of the alcohol lamp should be reduced as small as possible, or otherwise the steel may become overheated and lose all its good qualities. If needles are used for making drills there is a great liability of their warping when hardening, but when a larger piece of wire is used there is not much danger, if care is exercised in introducing the drill that it goes into the compound straight and point foremost. ”

“ For ordinary work these drills do very well, but for comparatively deep holes, or when using long, slender drills, some sort of a stand should be made, if for no other reason, to avoid breaking the drills, which is almost invariably due to the side motion of the hand. There are other reasons, however, for making such a stand, and these lie in the fact that it is impossible to drill by hand at right angles with the surface of the metal, or to hold such a drill sufficiently steady to avoid widening the hole around the top. ”

“ It will be obvious from these considerations that the more correctly the drill is ground, the longer it will last without regrinding, the greater its amount of feed may be to take an equal depth of cut, and the nearer the diameter of the hole drilled to that of the drill—the most correct results being obtained when the drill will closely fit into the hole it has drilled and will not fall through of its own gravity, a result it is somewhat difficult to attain. ”

“ For perpendicular boring the drill is mounted on a heavily weighted tripod, the inertia of which effectively damps all recoil from the shock of striking; for horizontal work, and sometimes for vertical, the support is a pillar wedged between the walls of the tunnel, or shaft. An ingenious detail is the rifled bar which causes the drill to rotate slightly on its axis [93] between every two strokes, so that it may not jam. ”

“ The drill is a most useful auxiliary to the eccentric cutter, not only for drilling holes, which it does with great nicety and speed, but also for making mouldings and patterns of various kinds. Unlike the cutter, which moves either in a large or small circle, the drill can only work upon its own centre, and therefore the size of the pattern depends upon the tool placed in it, its position being regulated by the screw in the sliding rest, into which it slips like the cutter. ”

“ As may have been conjectured, the noise which smote the book-keeper's ear was that of a drill. Although acutely discerned within, the sound was practically smothered on the outside of the vault.
At one end of the drill was a cavity, rapidly growing larger, in one of the steel panels. At its other end was a heavy, warty fist, part of the anatomy of Baptiste, the industrious mechanic. Baptiste held the drill while his comrade, Pierre, pounded it in. ”

“ It sometimes becomes convenient in the exigencies which occur in the work of a general machine shop to hold a drill in a dog or clamp and feed it into the work with the lathe dead centre. In this case the drill should be held very firmly against the dead centre, or otherwise the drill may, when emerging through the back of the hole, feed itself forward, slipping off the dead centre, and causing the drill to catch and break, or moving the work in the chuck, to avoid which the drill should have a deep and well countersunk centre. ”

“ It is similar to the flat drill but has its cutting edge bent forward. It possesses the keenness of the twist drill and the strength of the flat drill, but as in the case of all drills whose diameters are restored by forging and hand grinding, it is suitable for the rougher classes of work only, and requires great care in order to have it run true and keep both cutting edges in action. It is sometimes attempted to give a greater cutting angle to a flat drill by grinding a recess in the front face, as at a in Fig. ”

“ It is the essence of speed in drilling, for, unlike the necessary principles to be adopted in the percussion methods of drilling, the rotary drill does not have to be lifted from the hole for the purposes of clearing. The pulverized strata are continuously washed from the hole by a stream of water reaching the bottom of the drill. Very frequently, a pressure-fed mud is used, and this serves a double purpose, for in its return to the surface it tends to plaster the walls of the well. ”

“ The fewer times the steel is heated the better. My experience teaches me that you can do no better than to select some nice pieces of Stubb's steel for your pivot drills. Many watchmakers make their drills from sewing needles, say No. 3 or 4, sharps. The steel in these needles is usually of good quality, but the great drawback is that a drill made from a needle will not resist any great pressure, and is liable to break just at the time that you have arrived at the most important point. ”

“ A more efficient method of hand-drill work is, however, where one man holds the drill, and another swings the hammer or sledge. Another form of hand drill, called a churn drill, consists of a long, heavy bar of steel, which is alternately raised and dropped by the workman, thus cutting a hole by repeated impacts. ”

“ How to make Small Drills.—Then, again, to make small drills of steel wire, use the lamp for heating and tempering. If a small drill be broken, draw the temper in the lamp preparatory to forming it anew. Drills of larger size may be hardened in the forge fire, brightened by grinding or rubbing on a piece of fine emery cloth, and the temper readily drawn in the lamp. The same process may be applied to tempering small screw taps. Small screws can be readily blued in the same manner. ”

“ It proved a failure, as did one of smaller size, eight feet in diameter, tried subsequently. During and before the Hoosac tunnel work a number of boring-machines of similar character were experimented with at the Mont Cenis tunnel and elsewhere in Europe; but, like the American devices, they were finally abandoned as impracticable.
Hand Drills. —Briefly described, a drill is a bar of steel having a chisel-shaped end or cutting-edge. The simplest form of hand drill is worked by one man, who holds the drill in one hand, and drives it with a hammer wielded by his other hand. ”

“ The drills are light enough to be easily erected and dismantled, and compact, so that they can be used in restricted and out-of-the way places, while their simplicity entails little special training on the part of the workman. With pneumatic and other power-drills the cost of piercing holes for explosive charges is reduced to less than one-quarter of that of "jumping" with a crowbar and sledgehammers. With the hand method two men are required, usually more; one man to hold, guide, and turn the drill ”

“ When his first hole was bored, and his little drill raced wildly through into space, like the screw of a liner on the crest of a wave, he started a second, close beside the first; then a third, and a fourth, and a fifth, slowly honeycombing the thick steel with his minute excavations. Sometimes a drill would snap off short, and he would have to draw a fresh one from his stock. ”

“ The ordinary rock drill is really a pneumatic hammer. The tool, which is chisel-shaped, is used as a hammer to pound a hole in the rock. The tool is driven up and down or in and out by compressed air bearing alternately on opposite sides of a piston. The elasticity of the compressed air acts as a cushion to relieve the machine from shock. The drill is mounted upon a tripod in such a way that it may be operated in any direction. ”

“ He operated on a piece of hard diorite an inch and three-eighths in thickness, and employed as a drilling agent a wooden wand of ash, or at times, of pine, in conjunction with sharp quartz sand. Attached to the wand was a heavy disc, to act as a fly-wheel, and an alternating rotatory motion was obtained by means of a bow and cord attached at its centre to the apex of the drilling-stock, and giving motion to it after the manner of a "pump-drill," such as is used by the Dacotahs [100] and Iroquois [101] for producing fire by friction, or what is sometimes called the Chinese drill. ”