Modern Machine-Shop Practice Part 119

Fig. 1697 represents a special machine for boring pulleys, &c. The advantage possessed by this cla.s.s of machine is fully set forth in the remarks upon Boring and Turning Mills, and with reference to Fig. 725.

The tool bar is fed vertically to the rotating pulley, and has three changes of feed; viz. .0648, .0441, and .0279 of an inch per rotation of the work. Its weight is counterbalanced.

The speed of rotation of the work table or chuck plate may, by means of the four steps on the cone pulley, be varied as follows:--63, 43, 19, or 10 revolutions per minute, which speeds are suitable for work bores ranging from 1 to 7-1/2 inches in diameter, the power exerted at the tool-point being for the latter diameter 1800 lbs.

The tool bar feed is operated by the upper cone pulley, and the worm and worm-wheel shown, the small wheel giving the automatic feed by a suitable friction plate, and the large hand wheel operating the bar quickly to elevate it after it has carried its cut through. When the drill is given a traverse back and forth, it obviously cuts out a slot or keyway whose width is equal to the diameter of the drill, and whose length equals the amount of traverse given to the drill. Special forms of drill are used for this purpose, and their forms will be shown hereafter. The machines for using these drills are termed traverse or cotter drilling machines. In Fig. 1698 is represented a combined drilling and cotter drilling machine. This machine consists essentially of a drilling machine provided with automatic feed motions for cotter drilling; these motions consisting of a self-acting traverse to the sliding head carrying the drill spindle, and a vertical feed, which occurs at the end of each traverse, and during a short period of rest given to the sliding head carriage, or saddle as it is promiscuously termed. The slideway for this head stands vertical and extends across the top of the frame.

The belt motion is conveyed up one end and then on the top of the slideway, driving the spindle direct by means of a pulley. The traverse of the head or saddle in cotter drilling is accomplished by means of a peculiar arrangement of screws and adjustable nuts, which can be instantly set to the required length of slot, and insures a uniform motion, back and forth, at each stroke, the length of the stroke being uniform, as is also the rate of its advance. The vertical position of the drill spindle is of great advantage in cotter drilling wrought iron or steel, as the slot in process of cutting can be kept full of oil.

The feed motions for cotter drilling may be instantly thrown out of gear when not required, remaining at rest and leaving the machine a simple traverse drill with automatic feeds.

CHAPTER XIX.--DRILLS AND CUTTERS FOR DRILLING MACHINES.

DRILLING JIGS, GUIDES, OR FIXTURES.--When a large number of pieces are to be drilled alike, as in the case when work is done to special gauges, special chucking devices called jigs, or fixtures, are employed to guide the drill, and insure that the holes shall be pierced accurately in the required location, and test pieces or gauges are provided to test the work from time to time to insure that errors have not arisen by reason of the wear of these drill-guiding devices.

[Ill.u.s.tration: Fig. 1699.]

[Ill.u.s.tration: Fig. 1700.]

Suppose, for example, that we have a link, such as in Fig. 1699, and that we require to have the holes throughout a large number of them of equal diameter at each end and the same distance apart, and if we could prevent the wear of the tools, and so continue to produce any number of links all exactly alike, we could provide a simple test gauge, such as shown in the figure, making it pa.s.s the proper distance apart, and of a diameter to fit the holes; but as we cannot prevent wear to the tools we must fix a limit to which such wear may be permitted to occur, and having reached that point they must be restored and corrected. We must at the same time possess means of testing in what direction the wear has induced error. Let it be a.s.sumed that the bore at A should be 1/2 inch and that at B 3/8 inch in diameter, that their distance from centre is to be, say, six inches, and that either bore may vary in diameter to the amount of 1/1000 inch, while the distance from centre to centre of the bores may also vary 1/1000 inch. Now let it be noted that if one piece be made 1/2000 inch too short, and another 1/2000 inch too long we have reached the extent of the limit, there being 1/1000 inch difference between them, although neither piece varies more than 1/2000 inch from the standard. Similarly in the bore diameters, if the bore, say at A, is 1/2000 inch too large in one piece and 1/2000 too small in another, there is a difference of 1/1000 between them, although each varies only the 1/2000 inch from the standard. In making test gauges for the holes, therefore, we must consider in what direction the tool will wear; thus, suppose that the finis.h.i.+ng reamer for the holes is made when new to the standard diameter, and it can only wear smaller, hence a plug gauge of the standard diameter and 1/1000 inch smaller would serve thus, as so long as the smaller one will go in the limit of wear is not reached; when it will not go in sufficiently easily the reamer must be restored to fit the standard gauge. On the other hand, the reamer when new may be made 1/1000 inch above the standard size and restored when it has worn down to the standard size. In this case the bore diameter is still within the limit as long as the small gauge will enter; but when it fits too tight the reamer must be restored to the large plug gauge, the forms of these gauges being shown in Fig. 1700.

[Ill.u.s.tration: Fig. 1701.]

[Ill.u.s.tration: Fig. 1702.]

In Figs. 1701 and 1702 we have a jig or fixture for holding the link during the drilling process. It consists of two parts, C and D, between which the link is held by the screws E and F. The two hubs, G and H, are provided with hardened steel bushes, I and J, which are pierced with holes to receive and guide the drilling tool or reamer, and it is evident that in time the bore of these bushes will wear, and if they wear on one side more than on another they may wear longer or shorter between the centres or axis; hence we require gauges such as shown in Fig. 1703, one being longer between centres and the other shorter, in each case to the amount of the prescribed limit. In this case, so long as the holes are kept within the prescribed limit of diameter, the distance apart of the two holes will be within the limit so long as neither of the limit gauges will enter; and when they will enter the bushes I J must be restored.

It is to be remarked, however, that the variation in the diameter of the holes affects these standards, since if the holes are made sufficiently large either gauge would enter, although the axis of the holes and of the pins on the gauge might be the proper distance apart; hence the gauging for length depends to some degree upon the degree of accuracy in gauging for diameter.

[Ill.u.s.tration: Fig. 1703.]

Referring now to the construction of the jig, or fixture for drilling the link shown in Figs. 1701 and 1702: the base piece is provided with two short hubs, R and S, upon which the link is to sit, and it is obvious that these hubs must be faced off true with the bottom face of the base, while the link must also be faced so that it will be level, and not be bent or sprung when clamped by the screws E F. It is obvious that the hubs R and S may be omitted, and the link be flat on the base plate; but this would not be apt to hold the link so steadily, and greater care would be required to keep the surface clean. It is also obvious that in the form of jig shown there is a tendency of the screws E and F to bend the piece D; but in the case of small pieces, as, say, not exceeding 8 inches long, piece D may be made strong enough to resist the screw pressure without bending. If, however, the link were, say, 18 inches long, it would be preferable to have projections in place of the hubs R, S, and to let these projections extend some distance along each end of the link, using four holding screws, and clamping the piece D on the inside of the hubs H G. To facilitate the rapid insertion and removal of the link into and from the jig cap-piece, D is pivoted on screw F, while a slot V is cut at the other end, so that when the two screws E, F are loosened, the cap-piece D may be swung out of the way without entirely removing it.

[Ill.u.s.tration: Fig. 1704.]

[Ill.u.s.tration: Fig. 1705.]

[Ill.u.s.tration: Fig. 1706.]

[Ill.u.s.tration: Fig. 1707.]

In Fig. 1704 we have a link in which a hole is to be bored at one end at a certain distance from a pin at the other, and the fixture, or jig for drilling, is shown in the sectional view, Fig. 1705, the side view, Fig.

1706, and the top view, Fig. 1707. It is obvious that the pin P and the face W of the link must be made true, and that a hardened steel bush may be placed in the hub to receive the pin P. The screw E binds one end of the cap D, and eye-bolts with thumb-nuts F bind the other, these bolts being pivoted at their lower ends, and pa.s.sing through slots in D, so that as soon as nuts F are loosened, their bolts may be swung out clear of the cap, which may be swung on one side from the pin N as a pivot.

[Ill.u.s.tration: Fig. 1708.]

[Ill.u.s.tration: Fig. 1709.]

In Fig. 1708 we have a piece containing three holes, which are to be drilled in a certain position with regard to each other, and with regard to the face A. This brings us to the consideration that in all cases the work must be chucked or held true by the faces to which it is necessary that the holes must be true, and as in this case it is the face A, the jig must be made to hold the piece true by A, the construction being as in Fig. 1709, which represents a top view, and a sectional side view.

The upper plate D carries three hardened steel bushes, A, B, and C, to receive the drilling tools, and thus determine that the holes shall be drilled at their proper positions with relation to each other, and is provided with a face N, against which the face (A, Fig. 1708) may be secured by the screw H, and thus determine the positions of the holes with, regard to that face. At E, F, and G are eye-bolts for clamping the work between the cap and the base plate, which is made large so that it may lie steadily on the table of the drilling machine. When the nuts E, F, and G and the screw H are loosened the cap D may be lifted off and the work removed.

If the holes are required to be made very exact in their positions with relation to one edge, as well as to the face A of the work, two screws K would be required, one binding the cap against the lug M of the base, and the other binding the edge of the work against the same lug.

The usefulness of jigs, or fixtures, is mainly confined to small work in which a great many duplicate pieces are to be made, and their designing calls for a great deal of close study and ingenuity. They can obviously be applied to all kinds of small work, and as a general principle the holes and pins of the work are taken as the prime points from which the work is to be held.

Drilling fixtures may, however, be applied with great advantage to work of considerable size in cases where a number of duplicate parts are to be made, an example of this kind being given in the fixtures for drilling the bolt holes, &c., in locomotive cylinders.

[Ill.u.s.tration: Fig. 1710.]

For drilling the cylinder covers and the tapping holes in the cylinder, the following device or fixture is employed: The f.l.a.n.g.es of the cylinder covers are turned all of one diameter, and a ring is made, the inside diameter of which is, say, an inch smaller than the bore of the cylinder; and its outside diameter is, say, an inch larger than the diameter of the cover. On the outside of the ring is a projecting f.l.a.n.g.e which fits on the cover, as in Fig. 1710, _a_ being the cylinder cover, and _b_ _b_ a section of the ring, which is provided with holes, the positions in the ring of which correspond with the required positions of the holes in the cover and cylinder; the diameter of these holes (in the ring, or template, as it is termed) is at least one quarter inch larger than the clearing holes in the cylinder are required to be. Into the holes of the template are fitted two bushes, one having in its centre a hole of the size necessary for the tapping drill, the other a hole the size of the clearing drill; both these bushes are provided with a handle by which to lift them in and out of the template, as shown in Fig. 1711, and both are hardened to prevent the drill cutting them, or the borings of the drill from gradually wearing their holes larger. The operation is to place the cover on the cylinder and the template upon the cover, and to clamp them together, taking care that both cover and template are in their proper positions, the latter having a flat place or deep line across a segment of its circ.u.mference, which is placed in line with the part cut away on the inside of the cover to give free ingress to the steam, and the cover being placed in the cylinder so that the part so cut away will be opposite to the port in the cylinder, by which means the holes in the covers will all stand in the same relative position to any definite part of the cylinder, as, say, to the top or bottom, or to the steam port, which is sometimes of great importance (so as to enable the wrench to be applied to some particular nut, and prevent the latter from coming into contact with a projecting part of the frame or other obstacle): the positions of the cylinder, cover, template, and bush, when placed as described, being such as shown in Fig. 1712, _a_ _a_ being the cylinder, B the steam port, C the cylinder cover, D the template, and E the bush placed in position. The bush E having a hole in it of the size of the clearance hole, is the one first used, the drill (the clearance size) is pa.s.sed through the bush, which guides it while it drills through the cover, and the point cuts a countersink in the cylinder face. The clearing holes are drilled all round the cover, and the bush, having the tapping size hole in it, is then brought into requisition, the tapping drill being placed in the drilling machine, and the tapping holes drilled in the cylinder f.l.a.n.g.e, the bush serving as a guide to the drill, as shown in Fig. 1712, thus causing the holes in the cover and those in the cylinder to be quite true with each other. A similar template and bush is provided for drilling the holes in the steam chest face on the cylinder, and in the steam chest itself. While, however, the cylinder is in position to have the holes for the steam chest studs drilled, the cylinder ports may be cut as follows:--

[Ill.u.s.tration: Fig. 1711.]

[Ill.u.s.tration: Fig. 1712.]

[Ill.u.s.tration: Fig. 1713.]

The holes in the steam chest face of the cylinder being drilled and tapped, a false face or plate is bolted thereon, which plate is provided with false ports or slots, about three-eighths of an inch wider and three-fourths of an inch longer than the finished width and length of the steam ports in the cylinder (which excess in width and length is to allow for the thickness of the die). Into these false ports or slots is fitted a die to slide (a good fit) from end to end of the slots. Through this die is a hole, the diameter of which is that of the required finished width of the steam ports of the cylinder; the whole appliance, when in position to commence the operation of cutting out the cylinder ports, being as ill.u.s.trated in Fig. 1713, _a_ _a_ being the cylinder, B B the false plate, C the sliding die, and D D the slots or false ports into which the die C fits. Into the hole of the die C is fitted a reamer, with cutting edges on its end face and running about an inch up its sides, terminating in the plain round parallel body of the reamer, whose length is rather more than the depth of the die C. The operation is to place the reamer into the drilling machine, taking care that it runs true. Place the die in one end of the port, as shown in Fig. 1713, and then wind the reamer down through the die so that it will cut its way through the port of the cylinder at one end; the spindle driving the drill is then wound along. The reamer thus carries the die with it, the slot in the false face acting as a guide to the die.

In the case of the exhaust port, only one side is cut out at a time. It is obvious that, in order to perform the above operation, the drilling machine must either have a sliding head or a sliding table, the sliding head being preferable.

[Ill.u.s.tration: Fig. 1714.]

The end of the slot at which the die must be placed when the reamer is wound down through the die and cylinder port, that is to say, the end of the port at which the operation of cutting it must be commenced, depends solely on which side of the port in the cylinder requires most metal to be cut off, since the reamer, or cutter, as it may be more properly termed, must cut underneath the heaviest cut, so that the heaviest cut will be forcing the reamer back, as shown in Fig. 1714, _a_ being a sectional view of the cutter, B the hole cast in the cylinder for the port, _c_ the side of the port having the most cut taken off, D the direction in which the cutter _a_ revolves, and the arrow E the direction in which the cutter _a_ is travelling up to its cut. If the side F of the port were the one requiring the most to be cut off, the cutter _a_ would require to commence at the end F, and to then travel in the direction of the arrow G. The reason for the necessity of observing these conditions, as to the depth of cut and direction of cutter travel, is that the pressure of the cut upon the reamer is in a direction to force the reamer forward and into its cut on one side, and backward and away from its cut on the other side, the side having the most cut exerting the most pressure. If, therefore, the cutter is fed in such a direction that this pressure is the one tending to force the cutter forward, the cutter will spring forward a trifle, the teeth of the cutter taking, in consequence, a deep cut, and, springing more as the cut deepens, terminate in a pressure which breaks the teeth out of the cutter.

If, however, the side exerting the most pressure upon the reamer is always made the one forcing the cutter back, as shown in Fig. 1714, by reason of the direction in which the cutter is travelled to its cut, the reamer, in springing away from the undue pressure, will also spring away from its cut, and will not, therefore, rip in or break, as in the former case.

[Ill.u.s.tration: Fig. 1715.]

In cutting out the exhaust port, only one side, in consequence of its extreme width, may be cut at one operation; hence there are two of the slots D, Fig. 1713, provided in the false plate or template for the exhaust port. The cutter _a_ must, in this case, perform its cut so that the pressure of the cut is in a direction to force the cutter backwards from its cut. The time required to cut out the ports of an ordinary locomotive cylinder, by the above appliance, is thirty minutes, the operation making them as true, parallel, and square as can possibly be desired.

DRILLS AND CUTTERS FOR DRILLING MACHINES.--In the drilling machine, as in the lathe, the twist drill is the best tool that can be used for all ordinary work, since it produces the best work with the least skill, and is the cheapest in the end. As, however, the twist drill has been fully discussed with reference to its use upon lathe work, it is unnecessary to refer to it again more than to say that it possesses even greater advantages when used in the drilling machine than it does when used in the lathe; because as the drill stands vertical the flat drill will not relieve itself of the cuttings, and in deep holes must be occasionally withdrawn from the hole in order to permit the cuttings to be extracted, an operation that often consumes more time than is required for the cutting duty. Furthermore, as flat drills rarely run true they place excessive wear upon the drilling machine spindle, causing it to wear loose in its bearings, which is a great detriment to the machine.

Fig. 1715 represents a piece of work that can be readily drilled with a twist drill but not with a flat one, such work being very advantageous in cutting out keyways. All that is necessary is to drill the three holes B first, and if the drill runs true and the work is properly held and the drill fed slowly while run at a quick speed the operation may be readily performed.

The speeds and feeds for twist drills are given in connection with the use of the drill in the lathe, but it may be remarked here that more duty may be obtained by hand than by automatically feeding a drill, because in hand feeding the resistance of the feed motion indicates the amount of pressure on the drill, and the feed may be increased when the conditions (such as soft metal) permits, and reduced for hard spots or places, thus preserving the drill. Furthermore, the dulling of the drill edges becomes more plainly perceptible under hand feeding.

The commercial sizes of both taper and straight shank twist drills are as follows:--

--------+-------++-------+-------++-------+-------++--------+------- Dia- |Length.|| Dia- |Length.|| Dia- |Length.|| Dia- |Length.

meter. | ||meter. | ||meter. | ||meter. | --------+-------++-------+-------++-------+-------++--------+------- 1/4 | 6-1/8 || 25/32| 9-7/8 ||1-5/16 |14-1/4 ||1-27/32 |16-3/8 9/32 | 6-1/4 || 13/16|10 ||1-11/32|14-3/8 ||1-7/8 |16-1/2 5/16 | 6-3/8 || 27/32|10-1/4 ||1-3/8 |14-1/2 ||1-29/32 |16-1/2 11/32 | 6-1/2 || 7/8 |10-1/2 ||1-13/32|14-5/8 ||1-15/32 |16-1/2 3/8 | 6-3/4 || 29/32|10-5/8 ||1-7/16 |14-3/4 ||1-31/32 |16-1/2 13/32 | 7 || 15/16|10-3/4 ||1-15/32|14-7/8 ||2 |16-1/2 7/16 | 7-1/4 || 31/32|10-7/8 ||1-1/2 |15 ||2-1/32 |16-1/2 15/32 | 7-1/2 ||1 |11 ||1-17/32|15-1/8 ||2-1/16 |17 1/2 | 7-3/4 ||1-1/32 |11-1/8 ||1-9/16 |15-1/4 ||2-1/8 |17 17/32 | 8 ||1-1/16 |11-1/4 ||1-19/32|15-3/8 ||2-3/16 |17 9/16 | 8-1/4 ||1-3/32 |11-1/2 ||1-5/8 |15-1/2 ||2-1/4 |17-1/2 19/32 | 8-1/2 ||1-1/8 |11-3/4 ||1-21/32|15-5/8 ||2-5/16 |17-1/2 5/8 | 8-3/4 ||1-5/32 |11-7/8 ||1-11/16|15-3/4 ||2-3/8 |18 21/32 | 9 ||1-3/16 |12 ||1-23/32|15-7/8 ||2-7/16 |18-1/2 11/16 | 9-1/4 ||1-7/32 |12-1/8 ||1-3/4 |16 ||2-1/2 |19 23/32 | 9-1/2 ||1-1/4 |12-1/2 ||1-25/32|16-1/8 || | 3/4 | 9-3/4 ||1-9/32 |14-1/8 ||1-13/16|16-1/4 || | --------+-------++-------+-------++-------+-------++--------+-------

Twist drills are also made to the Stubs wire gauge as follows:--

+-----------------+---------++-----------------+--------+ |Numbers by gauge.| Length. ||Numbers by gauge.| Length.| +-----------------+---------++-----------------+--------+ | 1 to 5 | 4 || 31 to 35 | 2-5/8 | | 6 " 10 | 3-11/16 || 36 " 40 | 2-7/16 | | 11 " 15 | 3-1/2 || 41 " 45 | 2-1/4 | | 16 " 20 | 3-1/4 || 46 " 50 | 2-1/16 | | 21 " 25 | 3-1/16 || 51 " 60 | 1-3/4 | | 26 " 30 | 2-13/16 || 61 " 70 | 1-1/2 | +-----------------+---------++-----------------+--------+