Chapter V: Fastening Devices (2)

Another method is to split the nut across the end as shown in Fig. 420, tapping the nut with the split open, then closing the split by hammer blows. Here as before the nut would pass easily upon the bolt until the bolt reached the split, when the subsequent threads would bind. In yet another design, shown in Fig. 421, four splits are made across the end, while the face of the nut is hollowed, so that a flat place near each corner meets the work surface. The pressure induced on these corners by screwing the nut home is relied on in this case to spring the nut, causing the thread at the split end to close upon and grip the bolt thread.

Check nuts are sometimes employed to lock in position a screw that is screwed into the work, thus screws that require to be operated to effect an adjustment of length (as in the case of eccentric rods and eccentric straps) are supplied with a check nut, the object being to firmly lock the screw in its adjusted position.

The following are forms of nuts employed to effect end adjustments of length, or to prevent end motion in spindles or shafts that rotate in bearings.

Fig. 422 shows two cylindrical check nuts, the inner one forming a flange for the bearing. The objection to this is that in screwing up the check nut the adjustment of the first nut is liable to become altered in screwing up the second one, notwithstanding that the first be held by a lever or wrench while the second is screwed home.

Another method is to insert a threaded feather in the adjustment nut and having at its back a set screw to hold the nut in its adjusted position, as in Fig. 423. In this case the protruding head of the set screw is objectionable. In place of the feather the thread of the spindle may be turned off and a simple set screw employed, as in Fig. 424; here again, however, the projecting set screw head is objectionable. The grip of an adjustment nut may be increased by splitting it and using a pinching or binding screw, as in Fig. 425, in which case the bore of the thread is closed by the screw, and the nut may be countersunk to obviate the objection of a projecting head. For adjusting the length of rods or spindles a split nut with binding screws, such as shown in Fig. 426, is an excellent and substantial device. The bore is threaded with a right-hand thread at one end and a left-hand one at the other, so that by rotating the nut the rod is lengthened or shortened according to the direction of rod rotation. Obviously a clamp nut of this class, but intended to take up lost motion or effect end adjustment, may be formed as in Fig. 427, but the projecting ears or screw are objectionable.

Where there is sufficient length to admit it an adjustment nut, such as in Fig. 428, is a substantial arrangement. The nut A is threaded on the spindle and has a taper threaded split nut to receive the nut B. Nut A effects the end adjustment by screwing upon the spindle, and is additionally locked thereon by screwing B up the taper split nut, causing it to close upon and grip the spindle.

Lost motion in square threads and nuts may be taken up by forming the nut in two halves, A and B, in Fig. 429 (A being shown in section) and securing them together by the screws C C. The lost motion is taken up by letting the two halves together by filing away the joint face D of either half, causing the thread in the nut to bear against one side only of the thread of the screw. The same end may be accomplished in nuts for [V]-shaped threads by forming the nut either in two halves, as shown in Fig. 430, in which A is a cap secured by screws B, the joint face C being filed away to take up the lost motion. Or the nut may be in one piece with the joint C left open, the screws B crossing the nut upon the screw by pressure. In this case the nut closes upon the circumference of the thread, taking up the wear by closing upon both sides of the thread instead of on one side only as in the case of the square thread.

In cases where nuts are placed under rapid vibration or motion they are sometimes detained in their places by pins or cotters. The simplest form of pin used for this purpose is the split pin, shown in Fig. 431. It is made from half round wire and is parallel, and does not, therefore, possess the capability of being tightened when the nut has become loosened from wear. As the wire from which these pins are made is not usually a full half circle the pins should, if the best results are to be obtained, be filed to fit the hole, and in doing this, care should be taken to have the pin bear fully in the direction of the split which is longitudinal to the bolt, as shown in Fig. 432, where the pin is shown with its ends opened out as is required to prevent the pin from coming out. If the pin bears in a direction across the bolt as at A D, in Fig. 433, it will soon become loose.

Fig. 418.

Fig. 419.

Fig. 420.

Fig. 421.

Fig. 422.

Fig. 423.

Fig. 424.

Fig. 425.

Fig. 426.

Fig. 427.

Fig. 428.]

Pins of this class are sometimes passed through the nut itself as well as through the bolt; but when this is the case, there is the objection that the nut cannot be screwed up to take up any wear, because in that case the hole in the nut would not come fair with that in the bolt, and the pin could not be inserted. When, therefore, such a pin passes through the nut, lost motion must be taken up by placing an additional or a thicker washer behind the nut. The efficiency of this pin as a locking device is much increased by passing it through the nut, because its bearing, and, therefore, wearing area, is increased, and the pin is prevented from bending after the manner shown in Fig. 434, as it is apt to do under excessive wear, with the result that the end pressure of the nut almost shears or severs the pin close to the perimeter of the bolt.

To enable the pin to take up the wear, it is a good plan to file on it a flat place, which must be parallel to the sides of the pin-head and placed against the nut-face. The hole in the bolt is in this case made to fall slightly under the nut, as in Fig. 435, so that the flat place is necessary to enable the pin to enter. By filing the flat place taper, the lost motion that may ensue from wear may be taken up by simply driving the pin in farther.

In place of this class of split pin, solid taper pins are sometimes used, but these, if employed in situations where they are subject to jar and vibration, are apt sometimes to come loose, especially if they be given much taper, because in that case they do not wedge so tightly in the hole. But if a taper pin be made too nearly parallel, it will drive through too easily, and has less capability to take up the play due to wear. An ordinary degree of taper is about 5/8 inch per foot of length, but in long pins having ample bearing area, 1/2 inch per foot of length is ample. To prevent taper pins from coming loose from vibration, they are sometimes forged split at the small end, as in Fig. 436, and opened out at that end after the manner shown in Fig. 432. This forms a very secure locking device, and one easily applied. The split ends are closed by hammer blows to remove the pin, and it is found that such pins may be opened and closed many times without breaking, even though made of cast steel. The heads and ends are rounded so as to prevent them from swelling from the hammer blows necessary to drive them in and out. When a taper pin is passed through a nut and bolt, it simply serves as a locking device to secure the nut in position, and the lost motion due to wear must be taken up by the application of a washer beneath the nut, as already described. If, however, the taper pin be applied outside the nut, it may be made to take up the wear, by filing on it a flat place, and locating the hole in the bolt so that it will fall partly beneath the nut, as shown in Fig. 435. In this case, the nut may be screwed up to take up the wear, and the pin by being driven farther in will still bear against the nut and prevent its slacking back.

Another and excellent locking device for bolts or nuts, is the cotter shown in Fig. 437, which is sometimes forged solid and sometimes split, as in the figure. By being made taper from A to B, it will take up the wear if driven farther in. Its width gives it strength in the direction in which it acts to lock, the overhanging head is to drive it out by, and the bevelled corner C is to enable its easy insertion, because if left sharp it would be liable to catch against the edge of the cotter-way and burr up. If made split, its ends are opened out after it is inserted, as shown at D. When closing the ends of either split cotters or split pins to extract them it is better to close one side first and bend it over a trifle too much, so that, when closing the other side, by the time the pin is straightened the two ends will be closed together, and extraction becomes easy.

A very safe method in the case of a single nut or bolt head is to provide a separate plate, as in Fig. 438. The plate P is provided with three sides, corresponding to the sides of the hexagon, as shown, and in the middle of these sides are cut the notches A B C, so that by giving the nut N one-twelfth of a turn its corners D E would be held by the notches B C, S being a small screw to hold P. It is obvious that a simple set screw passed through the walls of the nut would grip the bolt thread and serve to hold the nut, but this would damage the bolt thread, and, furthermore, that thread would under jar or vibration compress and let the set screw come loose.

A better plan than this is to provide a thick washer beneath the nut and let a set screw pass through the washer and grip the bolt, fastening or setting up the set screw after the nut is screwed home. This, however, makes the washer a gripping piece and in no wise serves to lock the nut. In addition to the washer a pin may project through the radial face of the washer and into the work surface, which will prevent, in connection with the set screw, both the bolt and the washer from turning.

When a bolt has no thread but is secured by a taper pin, set screw, cotter, or device other than a nut, it is termed a pin. So, likewise, a cylindrical piece serving as a pivot, or to hold two pieces together and having no head, is termed a pin.

The usual method of securing a pin is by a set screw or by a taper pin and a washer; and since the term pin applying to both may lead to misunderstanding, the term bolt will here be applied to the large and the term pin to the small or securing pin only.

The object of pins and washers is to secure an exact degree of fit and permit of rapid connection or disconnection. An application of a taper pin and washer to a double eye is shown in Fig. 439. It is obvious, in this case, the pin E will drive home until it fills the hole through the bolt, and hence always to the same spot, so that the parts may be taken apart and put together again rapidly, while the fit is self-adjusting, providing that the pin fills the hole, bears upon the groove in the washer, and is driven home, so that by first letting the pin bind the washer W slightly too tight, and then filing the radial faces of the joint to a proper fit (which will ease the bearing of the pin on the washer), an exact degree of fit and great accuracy may be obtained, whereas when a nut is used it is difficult to bring the nut to the exact same position when screwing it home. When the joints are to be thus fitted, it is a good plan to drill the pin-hole (through the bolt) so that its centre falls coincident with the face of the washer; to then file out the grooves in the washer not quite deep enough. The pin may then be filed to fit the hole through the bolt, but left slightly too large, so that it shall not pass quite far enough through the bolt. The joint faces may then be filed true, and when finished, the parts may be put together, and the groove through the washer and hole through the bolt may be simultaneously finished by reaming with a taper reamer. This will leave the job a good fit, with a full bearing, without much trouble, the final reaming letting the taper pin pass to its proper distance through the bolt.

Taper pins are sometimes employed to secure in position a bolt that rotates, or one that requires locking in position, in situations in which there is no room for the bolt end to project and receive a nut or washer. Examples of these kinds are shown in section in Figs. 440 and 441. In 441, B is a stud pin, to rotate in the bore of A. C is a semi circular groove in B, and P a taper pin entering one-half in the groove C and one-half in B, thus preventing B from moving endwise in A, while at the same time permitting its free rotation. In this case it is best to fit B to its place, a fit tight enough to hold it firmly while the pin-hole is drilled and reamed through A and B simultaneously, then B can be put in the lathe, and the groove cut in to coincide with the half-hole or groove caused in the pin by the drilling, and after the groove is turned the stud pin may be eased to the required degree of working fit. The process for Fig. 440 is precisely the same, except that no groove turning or easing of the pin will be necessary, because the pin being locked in position may be left a tight fit. If, however, it is considered desirable to give the taper pin in Fig. 440 a little draft, so that any looseness (that may occur to the pin or stud) from wear may be taken up, then after the taper pin-hole has been drilled and reamed, the pin or stud (D in the figure) may be taken out, and its taper pin-hole _in the arm E_ may be filed out all the way through on one side, as denoted by the dotted half-circle. This will give draft to the pin and allow it to drive farther through and grip the pin as it wears smaller.

If a bolt and nut fit too tightly in their threads the nut may be wound back and forth upon the bolt under free lubrication, which will ease the fit by wearing away or compressing that part of the thread surface that is in contact. If this should not suffice we may generally ease a nut that fits so tight that it cannot be screwed upon the bolt with an ordinary wrench, by screwing the nut on a thread or two, then rest it on an iron block, and lightly hammer its sides; it will loosen its fit, and if continued, the nut may be made to pass down the bolt comparatively easily. Now, in this operation, it is not that the nut has been stretched, but that the points of contact on the threads have become compressed and imbedded; we have, in other words, caused the shape of each thread to conform nearer to that of the other than it is practicable to make them, because of reasons explained in the remarks on screw threads, and on taps.

To remove nuts or bolts that have become corroded in their places, we may adopt the following methods:--

If the nuts are so corroded that they will not unscrew with an ordinary wrench, we may, if the standing bolts and the wrench are strong enough to stand it, place a piece of gas or other pipe on the end of the wrench, so as to get a longer leverage; and, while applying the power to the wrench, we may strike the end face of the nut a few sharp blows with the hammer, interposing a set chisel, if the nut is a small one, so as to be sure to strike the nut in the proper place, and not rivet the screw end. If the joint is made with tap bolts we may strike the bolt heads with the hammer direct, using as before a light hammer and sharp blows, which will, in a majority of cases, start the thread, after which the wrench alone will usually suffice to unscrew it. If, however, this is not effective, we should take a thick washer, large enough in its bore to pass over the nut, and heat it to a yellow heat and place it over the nut, and the nut heating more rapidly than the stud or standing bolt, will be proportionately expanded and loosened; and, furthermore, the iron becomes stronger by being heated, providing the temperature does not exceed about 400°. If standing bolts or studs are employed on the joint, the heating is still advantageous, for the increase of strength more than compensates for the expansion. In this case the heating, however, may be performed more slowly, so that the hole may also become heated, and the bolt, therefore, not made a tighter fit by its excessive expansion. So also, in taking out the standing bolts or studs, heating them will often enable one to extract them without breaking them off in the hole, which would necessitate drilling out the broken piece or part. If, however, this should become necessary, we may drill a hole a little smaller than the diameter of the bottom of the bolt thread, and then drive into the hole a taper square reamer, as shown in Fig. 442, in which W represents the work, R the square reamer, and S the drilled screw end, and then, with a wrench applied to the reamer, unscrew the bolt thread. If this plan fails there is no alternative, after drilling the hole, but to take a round-nosed cape or cross-cut chisel and cut out the screw as nearly as possible, then pick out the thread at the entrance of the hole, and insert a plug tap to cut out the remaining bolt thread.

To take out a standing bolt, take two nuts and screw them on the bolt end; then hold the outer one still with a wrench and unscrew the inner one tightly against it. We may then remove the wrench from the outer or top nut, and unscrew the bolt by a wrench applied to the bottom or inner one. If the thread of a standing bolt has become damaged or burred, we can easily correct the evil by screwing a solid die or die nut down it, applying a little oil to preserve the cutting edge of the nut. If it is found impossible to take off a corroded nut without twisting off the standing bolt, it is the better plan to sacrifice the nut in order to save the bolt; and we may first hold a hammer beneath the nut, and take a cold chisel, and holding it so that the cutting edge stands parallel with the chamfered edge of the nut, and slanting it at an angle obtuse to the direction in which the nut in unscrewing would travel, strike it a few sharp blows, using a light hand-hammer; and this will often start it, especially if the nut is heated as before directed. The hammer held beneath the nut should be a heavy one, and should be pressed firmly against the square or hexagon side of the nut, the object being to support it, and thus prevent the standing bolt from bending or breaking, as it would otherwise be very apt to do. If this plan succeeds, the nut may, for rough work, be used over again, the burr raised by the chisel head being hammered down to close it as much as possible before filing it off. By holding the chisel precisely as directed, the seating of the nut acts to support it, and thus aids the heavy hammer in its duty. If this procedure fails we may cut the nut off, and thus preserve the bolt.

To do this, we must use a cross-cut or cape chisel, and cut a groove from the end face to the seating of the nut--a narrow groove will do, and two may be cut if necessary; light cuts should be taken, and the chisel should be ground at a keen angle, so that it will keep to its cut when held at an angle, as nearly parallel to the centre line of the length of the bolt as possible, in which case the force of the blows delivered upon the chisel head will be in a direction not so liable to bend the bolt. The groove or grooves should be cut down nearly to the tops of the bolt threads, and then a wrench will unscrew the nut or else cause it to open if one, and break in halves, if two grooves were cut.

After the nuts are all taken off, we may take a hammer and two or three wedges, or chisels (according to the size of the joint), and drive them an equal distance into the joint, striking one chisel first, and the diametrically opposite one next, and going over all the wedges to keep an equal strain upon each. If the joint resists this method, we may take a hammer and strike blows between the standing bolts on the outside face, interposing a block of hard wood to prevent damage to the face, and holding the wood so that the hammer strikes it endwise of the grain; and this will, in most cases, loosen the material of which the joint is made, and break the joint. If, however, the joint, after repeated trials, still resists, we may employ the hammer without the interposition of the wood, using a copper or lead hammer, if one is at hand, so as not to cause damage to the face of the work. To facilitate the entrance of the wedges, grooves should be cut in the joint of one face, their widths being about an inch, and their depth 1/16 inch.

WASHERS.--Washers are placed upon bolts for the following purposes. First, to provide a smooth seating for the nut in the case of rough castings. Second, to prevent the nut corners from marking and marring the surface of finished work. Thirdly, to give a neat finish, and in some cases to increase the bearing area of the nut and provide an elastic cushion to prevent the nut from loosening. Washers are usually of wrought iron, except in the case of brass nuts, when the washers also are of brass. The standard sizes adopted by the manufacturers in the United States for wrought iron washers is given in the following table:--

MANUFACTURERS' STANDARD LIST.

Adopted by "The Association of Bolt and Nut Manufacturers of the United States," at their meeting in New York, December 11th, 1872.

+-----------+---------+-------------+---------+
| Diameter. | Size of | Thickness | Size of |
| | Hole. | Wire Gauge. | Bolt. |
+-----------+---------+-------------+---------+
| 1/2 | 1/4 | No. 18 | 3/16 |
| 5/8 | 5/16 | " 16 | 1/4 |
| 3/4 | 5/16 | " 16 | 1/4 |
| 7/8 | 3/8 | " 16 | 5/16 |
| 1 | 7/16 | " 14 | 3/8 |
+-----------+---------+-------------+---------+
| 1-1/4 | 1/2 | " 14 | 7/16 |
| 1-3/8 | 9/16 | " 12 | 1/2 |
| 1-1/2 | 5/8 | " 12 | 9/16 |
+-----------+---------+-------------+---------+
| 1-3/4 | 11/16 | " 10 | 5/8 |
| 2 | 13/16 | " 10 | 3/4 |
+-----------+---------+-------------+---------+
| 2-1/4 | 15/16 | " 9 | 7/8 |
| 2-1/2 | 1-1/16 | " 9 | 1 |
| 2-3/4 | 1-1/4 | " 9 | 1-1/8 |
| 3 | 1-3/8 | " 9 | 1-1/4 |
| 3-1/2 | 1-1/2 | " 9 | 1-3/8 |
+-----------+---------+-------------+---------+

The various forms of wrenches employed to screw nuts home or to remove them are represented in the following figures. Fig. 443 represents what is known as a solid wrench, the width between the jaws a being an easy fit to the nuts across the flats. The opening between the jaws being at an angle to the body enables the wrench to be employed in a corner which would be too confined to receive a wrench in which the handle stood in a line with the jaws, because in that common form of wrench the position of the jaws relative to the handle would be the same whether the wrench be turned over or not, whereas with the jaws at an angle as in the figure, the wrench may be applied to the nut, rotating it a certain distance until its handle meet an abutting piece, flange, or other obstruction, and then turned over and the jaw embracing the same two sides of the nut the handle will be out of the way and may again operate the nut.

In some cases each end of the wrench is provided with jaws, those at one end standing at the same angle but being on the opposite side of the wrench.

The proper angle of the jaws to the centre line of the jaws may be determined as follows:--The most desirable angle is that which will enable the wrench to operate the nut with the least amount of wrench-motion, an object that is of great importance in cases where an opening has to be provided to admit the wrench to the nut, it being desirable to leave this opening as small as possible so as to impair the solidity of the work as little as practicable. For a hexagon nut this angle may be shown to be one of 15°, as in Fig. 444.

In Fig. 445, for example, the wrench is shown in the position in which it will just engage the nut, and at the first movement it will move the nut to the position shown in Fig. 446. The wrench is then turned upside down and placed upon the nut as in Fig. 447, and moved to the position shown in Fig. 448, thus moving the nut the sixth part of a revolution, and bringing it to a position corresponding to that in Fig. 445, except that it has moved the nut around to a distance equal to one of its sides. Since the wrench has been moved twice to move the nut this distance, and since there are six sides, it will take twelve movements to give the nut a full revolution, and, there being 360° in the circle, each movement will move the nut 30°, or one-twelfth of 360°, and one-half of this must be the angle of the gripping faces of the jaws to the body of the wrench. The width of the opening in the work to admit the wrench in such a case as in Fig. 445 must be not less than 30°, plus the width of the wrench handle, at the radius of the outer corner of the opening.

In the case of wrenches for square nuts it is similarly obvious that when the nut makes one-eighth of a revolution its sides will stand in the same position to receive the wrench that the nut started from, and in one-eighth of a revolution there are 45°. As the wrench is applied twice to the same side of the nut, its jaws must stand at one half this angle (or 22-1/2°) to the handle.

When a nut is in such a position that it can only be operated upon from the direction of and in a line with the axis of the bolt, a box wrench such as shown in Fig. 449, is employed, the cavity at B fitting over the bolt head; but if there is no room to admit the cross handle, a hub or boss is employed instead, and this hub is pierced with four radial holes into which the point of a round lever may be inserted to turn the wrench. Adjustable wrenches that may be opened and closed to suit the varying sizes of nuts are represented in Figs. 450, 451, and 452. In Fig. 450, A is the fixed jaw solid upon the square or rectangular bar E, and passing through the wooden handle D. B is a sliding jaw embracing E, and operated thereon by the screw C, whose head is serrated to afford a good finger grip. Various modifications of this form of wrench are made; thus, for example, in Fig. 451 A is the jaw, B a slotted shank, C the handle, all made in one piece. D is the movable jaw having a sleeve extension D´, and recesses which permit the jaw to slide on the shank longitudinally, but which prevent it from turning. The movable jaw is run to and from the nut or bolt head to be turned, by means of the screw G.

In another class of adjustable wrench the jaws slide one within the other; thus in Fig. 452, the fixed jaw of the wrench forms a part of the handle, and is hollowed out and slotted to receive the stem of the loose jaw, which plays therein, being guided by ribs in the slot, which take into grooves in the stem of the loose jaw. A screw with a milled head and a grooved neck serves to propel the loose jaw, being stopped from moving longitudinally by a partly open fixed collar on the fixed jaw, which admits the screw and engages the grooved neck of the same. The threaded extremity of the screw engages a female screw in the loose jaw, and while the same are engaged the screw cannot be released from the embrace of the fixed collar, as it requires considerable lateral movement to accomplish this.

Adjustable wrenches are not suited for heavy work because the jaws are liable to spring open under heavy pressure and thus cause damage to the edges of finished nuts, and indeed these wrenches are not suitable for ordinary use on finely finished work unless the duty be light. Furthermore, the jaws being of larger size than the jaws of solid wrenches, will not pass so readily into corners, as may be seen from the [S] wrench shown in Fig. 453. In the adjustable [S] wrench in Fig. 454, each half is provided with a groove at one end and a tongue in the other, so that when put together the tongues are detained in the grooves. To open or close the wrench a right and left-hand screw is tapped into the wrench as shown, the head being knurled or milled to afford increased finger-grip.

In all wrenches the location of contact and of pressure on the nut is mainly at the corners of the nut, and unless the wrench be a very close fit, the nut corners become damaged. A common method of avoiding this is to interpose between the wrench jaw and the nut a piece of soft metal, as copper, sheet zinc, or even a piece of leather. The jaws of the wrench are also formed to receive babbitt metal linings which may be renewed as often as required. To save the trouble of adjusting an accurately fitting wrench to the nut, Professor Sweet forms the jaws as in Fig. 455, so that when moved in one direction the jaws will pass around the nut without gripping it, but when moved in the opposite direction the jaws will grip the nut but not damage the corners, while to change the direction of a nut rotation it is simply necessary to turn the wrench over.

Fig. 456 represents a key wrench which is suitable for nuts of very large size. The sliding jaw J is held by the key or wedge S, which is operated by hammer blows. The projection at R is necessary to give sufficient bearing to the sliding jaw.

For use in confined places where but little handle-motion is obtainable, the ratchet wrench is employed, consisting of a lever affording journal bearing to a socket that fits the head of the bolt. The socket is provided with a ratchet or toothed wheel in which a catch or pawl engages. Fig. 457 represents the Lowell Wrench Company's ratchet wrench in which a lag screw socket is shown affixed. The socket is removable so that various sizes and shapes may be used with the same wrench. Each socket takes two sizes of square and one of hexagon heads or nuts. So long as the screw runs easily, it can be turned by the wooden handle more conveniently and faster than by the fingers, and independently of the ratchet motion. When this can no longer be done with ease, the twelve-inch handle is brought into use to turn the screw home.

For carriage bolts used in woodwork that turn with the nut notwithstanding the square under the head (as they are apt to do from decay of the wood or from the bolt gradually working loose) the form of wrench shown in Fig. 458 is exceedingly useful, it is driven into the wood by hammer blows at A. The bevelled edges cause the jaws to close upon the head in addition to the handle-pressure.

For circular nuts such as was shown in Fig. 411, the pin wrench or spanner wrench shown in Fig. 459 is employed, the pin P fitting into the holes in the nut circumference. The pin P should be parallel and slope very slightly in the direction of A, so that it may not meet and bruise the mouths of the pin-holes, A, B, C. The pin must, of course, pass easily into the pin-holes, and would, if vertical, therefore meet the edge of the hole at the top, bruising it and causing the wrench to spring or slip out, as would be the case if the pin stood in the direction of B.

It is obvious that to reverse the motion of the nut it is necessary to reverse the position of the wrench, because the handle end must, to enable the wrench to grip the work, travel in advance of the pin end. To avoid this necessity Professor Sweet forms the wrench as in Fig. 460, in which case it can operate on the nut in either direction without being reversed.

When a circular nut has its circumference provided with notches as was shown in Fig. 412 the wrench is provided with a rectangular piece as shown in Fig. 461. This piece should slope in the direction of a for the reasons already explained with reference to the cylindrical pin in Fig. 459. It is obvious, however, that this wrench also may be made upon Professor Sweet's plan, in which case the pin should be straight.

KEYS AND KEYWAYS.--Keys and keyways are employed for two purposes--for locking permanently in a fixed position, and for locking and adjusting at the same time. Keys that simply permanently lock are usually simply embedded in the work, while those that adjust the parts and secure them in their adjusted position usually pass entirely through the work. The first are termed sunk keys and keyways, the latter adjusting keys and through keyways.

The usual forms of sunk keyways are as follows:--Fig. 462 represents the common sunk key, the head _h_ forming a gib for use in extracting the key, which is done by driving a wedge between the head and the hub of the work.

The flat key, sunk key, and feather shown in Fig. 463, are alike of rectangular form, their differences being in their respective thicknesses, which is varied to meet the form of key way which receives them. The flat key beds upon a flat place upon the shaft, the sunk key beds in a recess provided in the shaft, and the feather is fastened permanently in position in the shaft. The hollow key is employed in places where the wheel or pulley may require moving occasionally on the shaft, and it is undesirable that the latter have any flat place upon it or recess cut in it. The flat key is used where it is necessary to secure the wheel more firmly without weakening the shaft by cutting a keyway in it. The sunk key is that most commonly used; it is employed in all cases where the strain upon the parts is great. The feather is used in cases where the keyway extends along the shaft beyond the pulley or wheel, the feather being fast in the wheel, and its protruding part a working fit in the shaft keyway. This permits the wheel to be moved along the shaft while being driven through the medium of the feather along the keyway or spline. The heads of the taper keys are sometimes provided with a set screw as in Fig. 464, which may be screwed in to assist in extracting the key.

Fig. 465 represents an application of keys to a square shaft that has not been planed true. The wheel is hung upon the shaft and four temporary gib-headed keys are inserted in the spaces _a_, _a_, _a_, _a_, in Fig. 465. (It may be mentioned here that similar heads are generally forged upon keys to facilitate their withdrawal while fitting them to their seats, the heads being cut off after the key is finally driven home.) These sustain the wheel while the permanent keys, eight in number, as shown in the figure at _b_, _b_, _b_, _b_, _b_, _b_, _b_, _b_, are fitted, the wheel being rotated and tested for truth from a fixed point, the fitting of the keys being made subservient to making the wheel run true.

The proportions of sunk keys are thus given by the Manchester (England) rule. The key is square in cross section and its width or depth is obtained by subtracting 1/2 from the diameter of the shaft and dividing the sum thus obtained by 8, and then adding to the subtrahend 1/4.

Example.--A shaft is 6 inches in diameter, what should be the cross section dimensions of its key diameter of shaft?

6 - 1/2 = 5-1/2, 5-1/2 ÷ 8 = .687, and .687 + .25 = 937/1000 inch.

In general practice, however, the width of a key is made slightly greater than its depth, and one-half its depth should be sunk in the shaft.

Taper keys are tapered on their surfaces A and B in Fig. 466, and are usually given 1/8-inch taper per foot of length. There is a tendency either in a key or a set screw to force the hub out of true in the direction of the arrow. It therefore causes the hub bore to grip the shaft, and this gives a driving duty more efficient than the friction of the key itself. But the sides also of the key being a sliding fit they perform driving duty in the same manner as a feather which fits on the sides A, D in Fig. 467, but are clear either top or bottom. In the figure the feather is supposed to be fast in the hub and therefore free at C, but were it fast in the shaft it would be free on the top face.

Fig. 468 represents a shaft held by a single set screw, the strain being in the direction of the arrow, hence the driving duty is performed by the end of the set screw and the opposite half circumference of the bore and shaft. On account, however, of the small area of surface of the set screw point the metal of the shaft is apt, under heavy duty and when the direction of shaft rotation is periodically reversed, to compress (as will also the set screw point unless it is of steel and hardened), permitting the grip to become partly released no matter how tightly the set screw be screwed home. On this account a taper key will under a given amount of strain upon the hub perform more driving duty, because the increased area of contact prevents compression. Furthermore, the taper key will not become loose even though it suffer an equal amount of compression. Suppose, for example, that a key be driven lightly to a fair seating, then all the rest of the distance to which the key is driven home causes the hub to stretch as it were, and even though the metal of the key were to compress, the elasticity thus induced would take up the compression, preventing the key from coming loose. It is obvious, then, that set screws are suitable for light duty only, and keys for either heavy or light duty. It is advanced by some authorities that keys are more apt to cause a wheel or pulley to run out of true than a set screw, but such is not the case, because, as shown in Figs. 466 and 468, both of them tend to throw the wheel out of true in one direction; but a key may be made with proper fitting to cause a wheel to run true that would not run true if held by a set screw, as is explained in the directions for fitting keys given in examples in vice work.

If two set screws be used they should both be in the same line (parallel to the shaft axis) or else at a right angle one to the other as in Fig. 469, so that the shaft and bore may drive by frictional contact on the side opposite to the screws. Theoretically the contact of their surface will be at a point only, but on account of the elasticity of the metal the contact will spread around the bore in the arc of a circle, the length of the arc depending upon the closeness of fit between the pulley bore and the shaft. If the bore is a close fit to the shaft it is by reason of the elasticity of the metal relieved of contact pressure on the side on which the set screw or key is to an amount depending upon the closeness of the bore fit, but this will not in a bore or driving fit to the shaft be sufficient to set the wheel out of true.

If two set screws are placed diametrally opposite they will drive by the contact of their ends only, and not by reason of their inducing frictional contact between the bore and the shaft.

A very true method of securing a hub to a shaft is to bore it larger than the shaft and to a taper of one inch to the foot. A bushing is then bored to fit the shaft and turned to the same taper as the hub is turned, but left, say, 1/100 inch larger in diameter and 1/4 or 3/8 longer. The bush is then cut into three pieces and these pieces are driven in the same as keys, but care must be taken to drive them equally to keep the hub true.

Feathers are used under the following conditions:--When the wheel driven by a shaft requires to slide along the shaft during its rotation, in which case the feather is fast in the wheel and the shaft is provided with a keyway or spline (as it is termed when the sliding action takes place), of the necessary length, the sides of the feather being a close but sliding fit in the spline while fixed fast in the wheel.

It is obvious that the feather might extend along the shaft to the requisite distance and the spline or keyway be made in the wheel: but in this case the work is greater, because the shaft would still require grooving to receive the feather, and the feather instead of being the simple width of the wheel would require to be the width of the wheel longer than the traverse of the wheel on the shaft. Nor would this method be any more durable, because the keyway's bearing length would be equal to the width of the wheel only.

When a feather is used to enable the easy movement of a wheel from one position to another a set screw may be used to fix the wheel in position through the medium of the feather as is shown in Fig. 470.

Through keys and keyways are employed to lock two pieces, and sometimes to enable the taking up of the wear of the parts. Fig. 471 represents an example in which the key is used to lock a taper shaft end into a socket by means of a key passing through both of them. When the keyway is completely filled by the key as in the figure it is termed a solid key and keyway, indicating that there is no draft to the keyway. Fig. 472 represents a key and keyway having draft. One edge, A C, of the key binds against the socket edges only, and the other edge E binds against the edge B of the enveloped piece or plug, so that by driving in the key with A hammer the two parts are forced together. The space or distance between the edge D and the key, and between edges E and F, is termed the draft. The amount of this draft is made equal to the taper of the key, hence, when the key is driven in so that its head comes level with the socket or work surface, the draft will be all taken up and the key will fill the keyway.

Draft is given to ensure all the strain of the key forcing the parts together, to enable the key to be driven in to take up any wear and to adjust movable parts, as straps, journal boxes or brasses, &c. When the bore of the socket and the end of the rod are parallel, the end of the rod F, Fig. 473, should key firmly against the end E of the socket, while the end D of the socket should be clear of the shoulder on the rod; otherwise instead of the key merely compressing the metal at F it will exert a force tending to burst the end F from G of the rod, furthermore, the area of contact at the shoulder D being small the metal would be apt to compress and the key would soon come loose.

In some cases two keys are employed passing through a sleeve, the arrangement being termed a coupling, or a butt coupling.

The usual proportions for this class of key, when the rod ends and socket boxes are parallel, is width of key equals diameter of socket bore, thickness of key equals one-fourth its width, with a taper edgeways of about 1/4 inch in 10 inches of length.

As the keys in through keyways often require to be driven in very tight, and as the parts keyed together often remain a long time without being taken apart and in some situations become rusted together, it is often a difficult matter to get them apart. First, it is difficult to drive it out because the blows swell the end of the key so that it cannot pass through the keyway, and secondly, driving the socket off the plug of the two parts keyed together often damages the socket and may bend the rod to which it is keyed. Furthermore, as the diameter of the socket is usually not more than half as much again as the diameter of the plug, misdirected blows are apt to fall upon the rod instead of upon the socket end and damage it. Hence, a piece of copper, of lead, or a block of wood should always be placed against the socket end to receive the hammer blows. To force a plug out of a socket, we may use reverse keys. These are pieces formed as shown in Fig. 474. A, A and B, B are edge and face views respectively of two pieces of metal, formed as shown, which are inserted in the keyway as shown in Fig. 475, in which A is the plug or taper end of a rod and B the socket, C is one and D the other of the reverse keys, while E is a taper key inserted between them, B driving E through the keyway, A and B are forced apart. The action of the reverse keys is simply to reverse the direction of the draft in the keyway so that the pressure due to driving E through the keyway is brought to bear upon the rod end in the part that was previously the draft side of the keyway, and in like manner upon the keyway in the socket on the side that previously served as draft.

Reverse keys are especially serviceable to take off cross heads, piston heads, keyed crank-pins, and parts that are keyed very firmly together.

Hubs are sometimes fastened to their shafts by pins passing through both the hub and the shaft. These pieces may be made parallel or taper, but the latter obviously secures the most firmly. If the pin is located as in Fig. 476, its resisting strength is that due to its cross sectional area at A and B. But if the pin be located as in Fig. 477 it secures the hub more firmly, because it draws the bore (on the side opposite to the pin) against the shaft, causing a certain amount of friction, and, furthermore, the area resisting the pressure of the hub is increased, and that pressure is to a certain degree in a crushing as well as a shearing direction.

If unturned pins are used and the holes are rough or drilled but not reamed, it is better that two sides of the pin should be eased off with a file or on the emery wheel, so that all the locking pressure of the pin shall fall where it is the most important that it should--that is, where it performs locking duty. This is shown in Fig. 478, the hole being round and the pin being very slightly oval (not, of course, so much as shown in the drawing), so that it will bind at A B, and just escape touching at C, D, so that all the pressure of contact is in the direction to bind the hub to the shaft.