Chapter XXVII: VICE WORK--(Continued) (2)

If the rod be large, the ends may be, and usually are, forged and fitted up separately, and subsequently welded to the body of the rod, which has been forged separately. In this case, the alignment of the parts is a part of the process in welding the rod, and setting it after welding. All the principles involved in making the rod ends separate, and afterwards welding them, or in marking out a small and complete forged rod, are, however, involved in the process of refitting an old rod in the jaws, and putting in new brasses; hence a description of that process will cover the whole ground. The first thing to do is to file up the side faces, as F, G, Fig. 2381, and, in doing this, all that is necessary is to file F up true, when tested by a straight-edge applied as in Fig. 2383, in which R is the fork and S a straight-edge, whose edge should measure the same distance at H as it does at I from the side face F, while the face C measures the same distance from face A of the other fork end, or from the imaginary centre line X, Fig. 2381. Then turning the rod on its side, a straight-edge should be placed across the face F, and one across the face G, as in Fig. 2384, at S and S´; and the edges of the two straight-edges should stand parallel, when sighted in such a position that the edges are very nearly in line with the eye, as shown in the figure.

The inside faces of the fork jaws may be filed to measurement from the outside ones.

The ways for the brasses should be filed square with the outside faces, as shown in Fig. 2385, in which S is a [T]-square; but if one jaw is wider than the other, as sometimes occurs, it will not matter, providing that, with the square applied, resting against the side and the face of the ways on the narrow jaw, the ways of the other jaw are equidistant from the square blade, as would be the case; for example, if the width of the ways of the jaw J extended to the dotted lines at K, L, because the line P would still form the centre line of both jaws, standing at a right angle to the side faces of the fork end, and parallel to the bore of the brasses at the butt end. Before filing up the side faces at the butt end, the strap should be fitted on and keyed up, so that its side faces may be filed up with those on the rod. To test the truth of the side faces at the butt end, a straight-edge should be applied, as at S and S´´, Fig. 2386, being pressed firmly to the side faces at the butt B, the fork faces being measured from the edge of the straight-edge at that end, and also with straight-edges, as in Fig. 2384. The brasses, after being fitted into the ways of the jaws, should have their joint faces squared, as in Fig. 2387, the top of each jaw being shown broken away, so as to fully expose the brasses. S is a square held firmly against the side face of a jaw, the brasses having their joint faces true with the square blade, and true also when tested with a square, applied as in Fig. 2388, in which B is the brass and S the square. The brasses at the other end should be filed true to the side faces of the strap in a similar manner, and, the fitting being completed, it simply remains to mark off the brasses for boring. The joint faces of the brasses should form the centre of their respective bores; hence, all that is necessary, is to insure that the brasses be of equal thickness, top and bottom, and this may be accomplished as follows: Mark across each face a line even with the ways of the brass, as shown in Fig. 2389, at A, C, and carry these lines around the side face, as shown in the figure at B, D. Place the brasses in the strap, put in a piece of wood whereon the compasses may be rested, as shown in Fig. 2390, which represents one jaw, and mark on this piece of wood a line even with the joint faces of the brasses, and on this line a centre-punch dot equidistant between the lines B, D. From this dot, as a centre, strike the circle shown, and define it by centre-punch dots, and if the lathe-hand chucks the brasses true to the ways that fit the rod jaws, and to the dotted circle, the bores will stand true in every respect.

REPAIRING CONNECTING RODS.--In repairing connecting rods the following is the work usually required to be done, and in the order named: Refitting straps, refitting gibs, and perhaps new gibs and keys, filing up the side faces of rod ends and straps, lining up brasses to make them fit the strap, lining up the rod to length and fitting the brasses together so as to fit their journals.

If the strap is taper and can be closed by pening, the outside of the back should be pened; but if the strap requires closing in the blacksmith's shop, then it should be tested by winding strips as shown in Fig. 2391, to insure that the faces are true, and thus save filing at the key ways and on the side faces to make them come fair with the rod ends. The rod ends should then be filed up and the straps fitted on.

Next comes putting in the new key and gib, or refitting the old gib. If the jaw of the gib has cut into the strap, as it will do in some cases (especially in marine and locomotive rods), this may be repaired as follows: Cut out the recess shown in Fig. 2392 at A, making it dovetail-shaped as shown, and with a set chisel set up its sides as shown in Fig. 2393, which is a sectional side elevation through the line of B. Cut out a piece of wrought iron and bevel its edges as shown in Fig. 2394, filing it to fit into the recess cut at A, Fig. 2392, and letting the bevelled edge be uppermost. Then take a set chisel and close down again upon the bevelled edge of the piece the metal that was set up, as shown in Fig. 2393, and the piece will be riveted, and it and the gib jaw may be refitted to touch the piece thus let in.

The jaws of the gib are sometimes made slightly taper at A, Fig. 2395.

To refit the brasses to the jaws of the strap, the flanges which do not as a rule wear much are usually tinned with a soldering iron, and given a lining of babbitt metal. This must be done all around the flanges (of both pairs of brasses) that come on the same side of the rod, so as to keep the faces of the brasses leading fair.

The fit between the jaws is restored by riveting pieces of sheet brass to that side of the brasses that has worn the most (usually the top which carries the weight of the rod). Fig. 2396 shows this operation carried out, A being the pieces of sheet brass which are sometimes soldered as well as held by rivets. These rivets are screwed into the brass, being composed of softened brass wire riveted after being screwed in.

If these pieces, which are called liners, are placed on the top of the brasses at one end, they should also be placed at the top of the brasses at the other end of the rod. They should not be less than about the 1/24 inch thick, the body of the brass being cut off to admit them if necessary.

In filing the joint faces of the brasses to let them together so as to take up the lost motion due to the wear of the brass bore and of the crank pin, the following considerations are met.

If the brass faces are to come "brass and brass," that is, butt together, when their bore is of the diameter of the journal, file those faces away until the bore appears just perceptibly too large for the journal, when measured with calipers, as in Fig. 2397, the bore measuring parallel all the way through. But, in doing this, it is necessary to be careful to file each brass so that it shall embrace one-half the journal diameter, which will be the case when the two brasses measure correctly as above, and alike, when tested, as in Fig. 2398, in which P is a planed surface, C a pair of inside calipers, and B a brass resting on P. When filing the joint faces, test them with a square as in Fig. 2399, in which _s_ is a square and B a brass, and also in Fig. 2400, in which _s_ is a square and B the brass shown in section, thus making the faces quite square.

The necessity of having their faces quite square when the brasses come brass and brass may be shown as follows:--

Suppose the joint to be at an angle as at A, A, Fig. 2401, instead of square across, as denoted by the dotted lines B, B, then the respective brasses will be forced by the key-pressure in the direction of the respective arrows, and there will be a tendency to twist the brasses in the strap. Or suppose the joint faces to be out of square as at C, C, instead of square as at D, then there will be a tendency to twist the respective brasses in the direction of E, F, and therefore to cause these to move in the direction of G, H, and as a result the brasses will spring the strap away from the rod, as shown at I, J.

To line up the brasses for length we proceed as follows: One of the liners adjusts the length of the rod and the other simply serves to set the key back to its proper height, so that it shall not pass too far through the keyway, as the wear of the brasses lets it down. Which of the liners will be the one by which to alter or adjust the length of the rod depends upon the design of the rod itself; but, in the case of all solid-ended rods, or those in which the position of the strap is fixed by means of bolts, it is the liner behind the end brass, as D, in Fig. 2402, as stated in the opening of this discussion, and it is the first one, therefore, to be fitted. The space at E is where the second liner requires to be placed, its thickness being that necessary to lift up the key from its bottom or lowest position, as shown in the cut, to the highest position.

In strap-ended rods in which the strap is not bolted to the rod, but moves farther upon the rod as the key passes farther through the keyway, it is the brass next to the rod end, as B, in Fig. 2403, by which to adjust the length of the rod, and its liner L is, therefore, the one to be fitted first; the space E is, in this case, the one to be fitted with a liner of sufficient thickness to lift the key up. It will now be noted that the thickness of L in both figures requires to be exact, so that the rod may be of correct length, which is necessary, so that there may be the same amount of clearance or space between the piston head and the cylinder cover when the piston is at the respective ends of the stroke. But the liners to fill the respective spaces E need not necessarily be of the exact thickness (although it is better that they should be), because if too thin the only effect will be that the key will pass farther through the keyway than otherwise. In considering in any form of rod which is the liner to be put in first to bring the rod to length, we have the general rule that the brass that moves in the strap or rod end when the key is moved farther through the keyway is the one to be lined last. The method of obtaining the proper thickness of the liners L, Figs. 2402 and 2403, are as follows: If the rods have been correctly made at first, the centre of the brass bores will be midway in the spaces for the brasses (denoted by F in the two figures). If the oil-holes in the strap or rod end (as the case may be) have been drilled in the centre of this space F as they should be, then the line _g_ will represent the centre of F and the centre of the oil-holes, and all that will be necessary will be to place behind D and B respectively a liner of sufficient thickness to bring the joint face of these brasses (D and B) even with the line _g_. To ascertain the thickness of liner necessary for this purpose, suppose the case of a rod end of the design shown in Fig. 2402, then, with the strap off the rod, drive the brass D down until its crown face beds fairly against the strap C, and with a scriber mark on the inside face of the jaw of the strap a line coincident with the joint face of the brass, then set the brass up the strap until its joint face comes fair with the centre of the oil-hole or the central line _g_, and then mark a second line so that on taking the brass out of the strap there will appear two lines, and the distance between these two lines is the necessary thickness of liner. In the case of the form of rod end shown in Fig. 2403, the process would be as follows: Let the strap have placed in it the brass B only, place it upon the rod, and set it so that it binds the gib and key, when the key is lifted up to its required position, then, with the brass B bedding fairly against the rod end, mark on the strap a line coincident with the joint face of the brass as before. Then move the brass in the strap until its face comes fair with the centre of the oil-hole or line _g_, and mark another line, and the thickness between these lines is the thickness of liner required at L.

If the brass is to be lined sufficiently to merely bring the key up without respect to the length of the rod we may drive the key home as in Fig. 2404, and mark on it a line coincident with the edge A of the strap. We then lift the key up to its proper height and mark a second line, so that when removed from the keyway the key will have on it the two lines shown in Fig. 2405, A being the first and B the second line; and the difference between the width of the key at A and its width at B will be the thickness of the liner necessary to be placed behind the brass nearest to the key. To ascertain the precise amount of this difference (because a very small error as to this amount causes a great deal of extra labor), we set a pair of outside calipers to the width at A; and then passing the caliper points down to B, we keep one of the points even with the line B, and insert a wedge until it just fills the space between the other point and the side of the key, as shown in Fig. 2406, C being the wedge, which should be chalked along its surface so that, when inserted until it touches against the caliper point, the latter will leave a mark on the wedge, denoting exactly how far the wedge entered, and hence the exact required thickness of liner.

It has thus far been supposed that the joint faces of the brasses are made to come brass and brass, that is to say, butt close together from the key pressure, when the brass bores properly fit the journal. Suppose, however, that the joint of the brass is left open as in Fig. 2407, and in that case a strip of metal F, whose diameter equals that of the journal, may be inserted between the brasses as shown, and at its centre should be provided a small centre-punch mark, denoting the centre of the bore. A piece of this kind should be inserted in the brasses at each end of the rod and placed in the middle of the length of the bore, the centre-punch marks being to apply the trammels to. Or if the rod was made of correct length when new, and the bore of the brasses, therefore, requires to stand central in space F, Fig. 2403, then the pieces F, Fig. 2407, may be dispensed with by marking a line B, Fig. 2408, central to space F, Fig. 2403. Then put the strap on the rod (with the brasses, gib, and key in place), and pull the strap back to hold the key up to its proper height.

The two brasses should then be placed as far apart as possible in the strap, each bedding fairly against its back or crown. Then, using the joint face of the back brass as a straight-edge or guide, a line should be marked on the side face of the strap, this line representing the position of that face when the brass is bedded fairly home, and being shown in Fig. 2408 at A. This brass should then be moved forward until the bore of the pair of brasses at D, Fig. 2408, measures equal to the diameter of the journal (of the crank pin or of the cross-head pin as the case may be) and a second line B, also coincident with the joint face of the brass, should be marked upon the strap, and the strap will then have marked on it the two lines shown in Fig. 2409, in which it is shown removed from the rod; the distance apart of these two lines will be the thickness of the two liners combined, hence half this thickness will be the thickness necessary for each liner. Suppose, however, that it is not known whether the rod has been correctly made, and therefore it be unknown whether, in order to have the rod of the correct length, the brass bore should stand in the centre of the space or not.

This is often the case in repairs, and sometimes on new rods, in which slight inaccuracies of workmanship are apt to occur. In this case it is best to mark a line, as G, in Fig. 2410, representing at each end of the rod the centre of the space F in that figure. Then set a pair of trammels to the correct length of the rod, and with one point of the trammel resting on the point at the intersection of line C with line D (the latter being the line G transferred to the centre of the bore) at the small end of the rod, we mark a line at the other end. If the lines D are too far apart, making the rod too long, the trammels will mark a line R, and the distance between lines R and D at the large end will be the amount the rod is too long, while half this distance will be the thickness of liner to go behind each bottom brass if the error of length is to be equally divided between the two ends of the rod, in which case a line T, midway between D and R, must be marked, the trammel then being rested on T, and the line S marked. These two lines, S and T, are then the centre lines for the bores of the brasses.

If it is determined that one pair of brasses shall be central in its space F, all the error being thrown on the other pair, this may be done by lining one pair up so that its bore is true to line D, and putting behind the back brass at the other end a liner whose thickness is equal to the distance between D and R at the large end of the rod. It is obvious that the measurement for rod length must be taken on the line C.

Having thus determined what thickness of liner is necessary to bring the rod to its proper length, it remains to find the thickness of liner necessary for the other half brass, to bring the key up to its proper position, the process for which has already been explained. After, however, the various liner thicknesses have been found, and the sheet metal selected to cut them from, it is well to try if the thickness is correct by cutting off a small piece of the metal, putting it in place behind the brass, and then, after keying up the brasses, the rod length may be trammelled.

As the liners placed behind connecting-rod brasses require to be very finely bedded, the facility with which their forms permit them to be fitted is an important consideration.

In Fig. 2411 is shown the forms commonly given, the requisite form of liner being shown beneath each. Form 1 will bed very firmly to its seat, but it will be observed that its liner is a difficult one to make, the bottom section A being thicker than the sides or wings B. This is a troublesome form of liner to fit as well as to make. If it be made of wrought iron, the wings B must be either forged or filed to their reduced thickness.

In the form at 2 in the figure we have the same defect, while in addition the liner will not adjust itself so readily in position to its bed.

This latter is an easier form to make in the moulding pattern, and easier to mould, and somewhat easier to fit, but it is not so firm as the first. To cause this form of brass to bed easily to its proper position it is sometimes given a lug on the bottom, as at 3 in the figure, the lug extending part of the width across only, because if it extended fully across, the liner would require to be in two pieces, causing trouble both in fitting them and in getting them into their places. When the lug extends partly across, the liner must have a slot to pass over and admit the lug, and this causes trouble in bending the liner to the required curve.

In the form shown at 4 in the figure all these difficulties are avoided, while, if the lower corners are made square instead of rounding, a simple piece of sheet metal will serve as a liner requiring but little fitting and bedding if it be of the proper thickness.

To fit up a link motion, assuming the machine work to be done, the first thing to do is to face up the side faces of the links, making them parallel, and true to a surface plate. The slot is then filed out square to the side faces, its curve being filed to a template T, Fig. 2412, which is provided with a piece of wire for a handle. It is supplied with red marking, and is rubbed upon the slot to mark the high spots. The same template may be used to prepare the link block or die; but as soon as the block can be moved in the slot with slight hammer blows (using a mallet or a block of wood) it should be used instead of the template, the bearing marks serving to correct and finish the block as well as the slot. In filing up the block care should be taken to make it of even thickness on each side of its hole and with its sides parallel to the hole, the latter being of great importance. When the block is a sufficiently easy fit in the slot to permit it, a round stick of wood may be put through it and used to move it up and down the link slot for the marking process.

The next operation is to fit the eccentric rod eyes to the link, and to then ream out the holes in both the link and the eyes while they are put together. The block may then be placed in the link, and the rocker pin passed through the block and into the rocker arm, so that the working fit of these parts when put together may be tested and adjusted if necessary. The link hanger may then be fitted to the saddle pin, when the whole will be ready for the file finishing and polishing, after which it may be case-hardened.

CASE-HARDENING.--Case-hardening consists in the conversion of the surface of wrought iron into steel, or in converting the grade of a low steel into a sufficiently high grade to render it capable of hardening. The depth to which this conversion occurs depends upon the material used to produce it, and the length of time the process is continued, varying from 1/64 inch under the prussiate of potash process to 1/16 or 1/8 inch in the case of long-continued box case-hardening.

Work that is thoroughly case-hardened has a dull white, frosted-looking surface. If the surface of the work is mottled, or has patches of fancy water-mark colors, it may be hard, but it is not so to the highest attainable degree.

To thoroughly test this, take a new dead-smooth file and apply its corner edge under heavy pressure to the work on an edge where the fancy colours are, and then on an edge where the surface is white, and the latter will be found to be the hardest as well as hardened the deepest.

The simplest method of case-hardening is by the prussiate of potash process, for which it is essential that the prussiate of potash be finely powdered, and contain no small lumps. The piece being heated may then, if small, be dipped in the prussiate of potash, or if large have the same spread upon it. In either case, however, the work must be hot enough to cause the potash to fuse and run over the work surface, and this action may be assisted by using a piece of iron wire, spoon-shaped at the end, wherewith to apply potash to the work and rub it upon the work surface.

After the potash has thoroughly fused and run over the entire surface of the work it will usually have become somewhat cooled, and will require reheating before quenching in the water.

If this reheating be done in the blacksmith's fire, it is not well to put the blast on; it is better to let the blast on gently while applying the potash to the work, so as to have a live clear fire to put the work in, and reheat it with the blast turned off.

While the work is in the fire it should be constantly rotated, not only to heat it evenly, but to let the adhering potash run over the entire surface, and as soon as the required heat is attained the work should be removed from the fire quickly and quenched in water.

It may be added, however, that if after the potash has been applied and fused more potash be added, so that it will adhere to the work and not fuse until the work is put into the fire a second time, then, after the work is quenched and taken from the water, there will be found on it a thick white and closely adhering fur of melted potash, and the work will be a dead white, with no fancy colors on it, and as hard as it is possible to make it.

The prussiate of potash process is, of course, from its expensiveness, both in material and labor, too costly for work to be done in quantities, and box-hardening is therefore resorted to.

In box case-hardening the work is case-hardened all over. It consists in packing the work in an iron box containing the hardening material, and subjecting the whole to a cherry-red heat for some hours.

A very common process is to fill a sheet-iron box with the work closely packed about with bone-dust, the pieces of the work having at least a thickness of 3/8ths of an inch of bone-dust around them. The seams of the box are well luted with clay to prevent the gases from the consumed bone-dust from escaping, and to exclude air.

Various ingredients are used to effect case-hardening. One process is as follows: 20 lbs. of scrap leather and 15 lbs. of hoofs (cut into pieces of about an inch square), 4 lbs. of salt, and one gallon of urine are prepared, and a wrought iron box with a lid capable of being fastened on is obtained. The fastenings must be capable of ready unfastening when hot. A layer of leather and pieces of hoofs about 1-1/2 inches thick is first laid in the box, then a layer of salt, and then a layer of work. Leather and hoof are then packed closely around the work and above it for a thickness of about an inch, and a second layer of work added, and so on, the last layer being of leather, &c., completely filling the box; the urine is then added, and the box well sealed with clay.

The box is placed in a furnace and kept at a red heat for about fourteen hours, and is then taken to a deep tank, and the work quickly immersed, so as not to be exposed to the air after the box is opened.

If the pieces are of solid proportions, so as not to be liable to bend or warp in the cooling, the contents of the box are simply dumped into the tank, the water being allowed to flow freely in the tank to keep up a circulation and cool the work quickly; some work, however, requires careful dipping to prevent it from warping. Thus a link or a double-eye would be dipped endwise, a plate edgewise; but all pieces should be immersed as quickly as possible after the box is opened.

Sheehan's patent process for box case-hardening, which is considered a very good one, is thus described by the inventor:

DIRECTIONS TO MAKE AND USE SHEEHAN'S PATENT PROCESS FOR STEELIFYING IRON.

No. 1 is common salt.

No. 2 is sal soda.

No. 3 is charcoal pulverized.

No. 4 is black oxide of manganese.

No. 5 is common black rosin.

No. 6 is raw limestone (not burned).

Take of No. 1, 45 lbs., and of No. 2, 12 lbs. Pulverize finely and dissolve in as much water as will dissolve it and no more--say 14 gallons of water in a tight barrel; and let it be well dissolved before using it.

Then take three bushels of No. 3, hardwood charcoal broken small and sifted through a No. 4 sieve. Put the charcoal in a wooden or iron box of suitable size made water-tight.

Next take of No. 4, 5 lbs., and of No. 5, 5 lbs., the rosin pulverized very fine. Mix thoroughly No. 4 and No. 5 with the charcoal in your box.

Then take of the liquid made by dissolving No. 1 and No. 2 in a barrel as stated, and thoroughly wet the charcoal with the whole of said liquid, and mix well.

The charcoal compound is now ready for use.

A suitable box of wrought or cast iron (wrought iron is preferable) should next be provided, large enough for the work intended to be steelified.

Now take No. 6, raw limestone broken small (about the size of peas), and put a layer of the broken limestone, about 1-1/2 inches thick, in the bottom of the box. A plate of sheet iron, one-tenth of an inch in thickness, is perforated with 1/4-inch holes one inch apart. Let this plate drop loose on the limestone inside the box. Place a layer of the charcoal compound, two inches thick, on the top of said perforated plate. Then put a layer of the work intended to be steelified on the layer of charcoal compound, and alternate layers of iron and of the compound until the box is full, taking care to finish with a thick layer of compound on the top of the box. Care should also be taken not to let the work in the box come in contact with the sides or ends of the box. Place a suitable cover on the box and lute it with fire-clay or yellow mud. The cover should have a quarter-inch hole in it to permit the steam to escape while heating.

The box should now be put in an open fire or furnace (furnace preferred), and subjected to a strong heat for five to ten hours, according to the size of the box, and the bulk of iron to be steelified. Remove the pieces from the box one by one and clean with a broom, taking care not to waste the residue, after which, chill in a sufficient body of clear, cold water, and there will be a uniform coat of actual steel on the entire surface of the work to the depth of 1/16 or 1/8 of an inch, according to the time it is left in the fire. The longer it is left in the fire the deeper will be the coat of steel.

Then remove the residue that remains in the box, and cool with the liquid of No. 1 and No. 2, made for the purpose with 20 gallons of water, instead of 14 gallons, as first used with the charcoal compound.

The residue must be cooled off while it is hot, on a piece of sheet iron or an iron box made for the purpose. Turn the residue into the supply box, and it will be ready for use again. The more it is used, the better and stronger it will be for future work.

There is nothing to be renewed for each batch of work but the limestone, and that, after each job, will be good burned lime.

A process used at the Elevated R.R. shops in New York city is as follows: The materials used are: leather, 1 part; bone dust, 5 parts; salt, 1 part. Heat for 48 hours to a red heat in a box sealed with fire clay, and quench in a solution of 3 pounds of potash to 30 gallons of water.

The wrought iron thus treated is impervious to a new smooth file at a depth of 1/16 of an inch.

The potash water is said to prevent both warping and the formation of blister marks on the work.

The durability of work case-hardened is greatly enhanced, but it is an expensive process; not so much by reason of the cost of it, but because it involves resetting and a refitting of the parts. The resetting is necessary because the work warps under or during the process. This warping can be prevented to some extent by placing the heaviest pieces in the bottom of the box, and so packing the same that the weight of the top pieces shall not tend to bend those beneath them when the hardening material has burned away, and so placing the upper pieces that they shall not be bent by their own weight. Thus both in packing and locating the work in the box the utmost care is necessary.

SETTING WORK AFTER HARDENING IT.--Work that has been hardened or case-hardened usually swells during the hardening process, and therefore requires refitting afterwards. This swelling usually occurs in all directions, thus holes and bores become of smaller dimensions, while the outside dimensions also increase, bolts become of larger diameter and sometimes increase in length.

In very exceptional cases, however, the dimensions of a piece of work will not alter.

This renders it usually necessary to refit the work after it has been hardened, thus holes which are ground out by laps or bolts may be ground to diameter in a grinding lathe.

In some practice, however, the work to be hardened is made a somewhat too easy fit, the holes tapped out and the bolts ground in by direct application of the bolts to their holes in connection with flour emery and oil. This latter plan is also adopted for forms not easily ground out in a machine, as, for example, a die in a link of a link motion.

To prevent surfaces or forms of this class from altering their shape or dimensions during the hardening process, slips of iron are sometimes fitted to them before they are placed in the hardening box. Thus Fig. 2414 represents a double eye, and Fig. 2413 a link having thin pieces fitted in as shown at A in both figures.

The heating for the hardening process is also apt to impair the alignment of the work, causing it to require resetting by the aid of parallel strips and straight-edges.

The faces of the link having been set, the width of the link slot must be set, for it may open or close in places. If it opens it may be closed by the jaws of a powerful vice, while if it closes it may be opened by a pair of inverted keys, inserted as shown in Fig. 2415, and driven in by the hammer. At each trial, however, a mark should be made on the driven key, so that it may be known how far to drive it at the next trial.

Fig. 2416 represents a link that is supposed to have been case-hardened, and to therefore require resetting. The stem from A to B should first be straightened to a straight-edge on both its side and edge faces. It should then be tested for winding with the winding strips, C, D, placed as in Fig. 2416, and then as in Fig. 2417.

To test the alignment of end E, press a straight-edge S fair against its side face, as in Fig. 2418, and measure the distance H. Then place the straight-edge on the other side face of E and measure the distance I, Fig. 2419, and these distances both measuring alike, E will be true providing that the jaws at end F have not altered from their proper width apart.

To test the alignment of the jaws at end F, press a straightedge against the outside face of the hub and measure the distance J, Fig. 2420, then apply it on the other side and measure distance K, Fig. 2421, and when distances J and K are equal and the width L between the jaws is correct, end F is in line in one direction. To test it in the other direction, apply a pair of parallel strips, placing one on end E as in Fig. 2417, and the other across the face of the hub of end F to see if there is any twist.

Suppose, however, that distances J K are unequal, then if distance L is too narrow (when tested by the piece that fits between the jaws) then the jaw at F that gives the widest distance at E is the one that requires correction, or if distance L is too wide, the jaw that shows the least distance at end E is the one requiring correction.

The link should be warmed to about 300°, or nearly _black_ hot, and pieces of sheet copper placed between the work and the anvil, and between the blacksmith's tools and the work, so that the latter may not be bruised by the blows delivered to effect the straightening.

After the process has been performed at each end individually the testing should be repeated, because setting the end F may have impaired the setting of end E, in the alignment to F.

It is obvious that the same setting or aligning process would be required in the case of a large link, where the ends were forged separately and welded to the body after the machine work and fitting had been done to them.

FITTING BRASSES TO BOXES OR TO PILLAR BLOCKS.--In the operation of fitting brasses to their boxes or to pillar blocks there are two things to be especially guarded against: First, having the brass let down one-sided, as shown in Fig. 2422; and next, aslant, as shown in Fig. 2423. The first depends on taking the proper amount off the two side faces, and the second in cutting the inside of the flanges fair. To cut the side faces fair, grip the brass in the vice, as shown in Fig. 2424 (the brass being shown in section), in which a is A block of wood. Take the measure of the box, down where the brass will come when home, and, if there be any taper to the box, set the inside calipers to the top of the location for the brass, and after the brass is in the vice place a square under one side-face, as at B in Fig. 2426, and see how much there is to come off. This saves the use of outside calipers, and is better because, not only is the trouble of setting the latter avoided, but the inside calipers can be tried to the box and the work in an instant, and a correction can at once be made if the calipers have got shifted. The cape chisel, or cross-cut, as it is sometimes termed, should first be used, taking a cut close to the flange, and making it half as deep as the calipers (applied as shown in Fig. 2426) show there is metal to come off. Then a similar cut should be taken close to the other flange, especial care being taken to take both cuts equally deep, and leaving as much to come off the other side face of the brass; otherwise, the brass will come atwist. Then take a straight-edge, and, placing its edge fair with the two chisel-grooves, while holding it firmly against the joint face of the brass, mark a line running from one chisel groove to the other; this line serving as a guide for the depth of all the other cape-chisel grooves. Now cut off the intermediate spaces with the flat chisel, using a straight-edge as a guide. If the box is taper, chip the side face to a corresponding taper, using a bevel-square, or estimating the amount by the eye if it is not too much. Now file the chipped surface flat and true, and then turn the brass upside down, gripping it with the wood as before, and dress the other side face (applying the inside calipers as in Fig. 2426), and bring that face down to within about 1/64 inch of the size to which the calipers are set. If the block of wood is made a little shorter than the length of the brass, the calipers can be applied without moving the brass from or in the vice. The method of applying the square to these side faces is shown in Fig. 2425, in which A is the brass in section, B a straight-edge, and C a square.

We now turn our attention to the flanges, and apply a square to the crown of the box, bringing the edge of the blade fair with the edge of the box, as shown in Fig. 2428, A representing the box in section, and B the square. Supposing the crown of the box to stand square, as shown in the engraving, and as it should do, we set the brass upon a truly-surfaced iron plate and square up the joint face, as shown in Fig. 2427, in which A is the surfaced iron, B the brass, and C the square. Since, however, the joint face of the brass may not be parallel with the crown face, we may place the square so that its blade edge comes fair with the crown face--that is, as shown at D in Fig. 2427--and set the brass crown (by means of inserting a wooden wedge under its face) truly perpendicular or parallel with the square blade edge. Now try the square with the side face of the brass, setting the latter true with the square blade, as in Fig. 2430; A being the iron plate and B the square; and, supposing the box to be true, as it usually is, we may set a scribing-block, as shown in Fig. 2427, and mark off how much is to come off the flanges by scribing a line around the flange, sufficiently depressing the scriber-point to allow an equal amount to come off each of the flanges. Sometimes, however, the inside faces of the box are not true with the outside face. To test this, we place a straight-edge across the outside face, place a square on it, and apply it to the inside face of the box, as in Fig. 2429, which is a plan view of the box, A being the straight-edge and B the square. If the square thus applied shows a want of truth in the box, we may set the brass over when adjusting it (as in Fig. 2427) to a corresponding amount, and thus mark off the flanges to suit the box.

To hold the brass while operating on the flanges, we resort to the device shown in Fig. 2431, in which A is a bolt, B the brass, C a piece of hard wood, and P a clamp fastened down by a nut D. To sustain the plate P, so that it shall not fall down on the piece of wood every time the brass is taken out to try it in the box, we may insert the spiral spring S, shown in the separate view of the bolt, nut, and plate. One such holding device will do for different sizes of brasses, by either gripping the bolt lower down in the vice jaws or putting washers between the nut and the plate. This will hold the brass very firmly, and at the same time leave the whole of the flange easily got at. When the flanges are dressed, we may try the brass in the box, putting red-lead marking on the box to mark where the brass binds. While letting the brass down, however, we must be careful to let it down fair, to avoid the state of things shown in Figs. 2422 and 2423. A ready method of doing this is (supposing the box to be true, as it should be, and making the necessary allowance if it is not), to set a pair of inside calipers to the joint face of the brass and the top of the box, as shown in Fig. 2432, trying the calipers (in the two positions there shown) on both sides of the box. This should be done every time the brass is tried in the box, until such time as the brass begins to bed against the bottom of the box.

We now come to the bedding of the brass to its seat in the box. This requires skillful treatment; for one mistake will involve a great deal of extra work to rectify it.

In fitting the brass to the box care must be taken to leave it a rather tighter fit to the box than it requires to be when finished, that is after the bore has been made, because in the boring operation the sides of the brass are apt to close and loosen the fit of the brass to the box.

When the side faces and flanges are so far fitted as to render probable the brass driving home at the next trial, the bed of the box should be given a coat of red-lead marking, and small pellets of stiff red lead or putty should be stuck on the bottom of the box, two at each end of each bevel, and two at each end of the bottom, with one in the middle of the bottom and each bevel, as shown at A, B, C, D, E, F, in Fig. 2433, by the black spots. Then when the brass comes home, it will flatten these pellets, and their thickness (when the brass is taken out) will show how much the bevels are out, and how much to take off the brass to make it bed. These pellets _must_ be restored to their original shape every time the brass is tried; otherwise, they may mislead. To insure their sticking to the box, and not coming out with the brass, the bottom of the box must have red-lead marking kept upon it. The chipping should continue until the pellets flatten out equally on the two bevels, but are left a little thicker on the bottom. If this is not done, the bottom will bed first, causing a great deal of extra filing, because filing the side bevels will let the bottom down too far.

In driving the brass in and out of the box while fitting it, a piece of wood must be used to strike on, otherwise the brass will stretch during the fitting and come loose in the box during the boring.[33]

[33] See remarks on Pening, p. 162.

The patterns from which the castings for brasses are moulded should not be made of the same angle or sweep on the bedding part or bottom as the bottom of the box, pedestal, or pillar block, because the brass casting, in cooling in the mould, contracts across the bore; thus if in Figs. 2434 and 2435 the full lines denote the shape of the pattern the dotted lines denote the shape the casting will be.

The result of this is that when the brass is let down in the box it will bed on the crown and not at the sides. Thus in Fig. 2436, A is a pedestal, and B a brass which beds at C, but not at D or E. In Fig. 2437 is shown an example of a brass, with a circular bottom, which would bed at the crown C, but not at the sides D E, until the metal was cut down to the dotted circle F.

The amount to which this contraction in the mould occurs varies with the size of the brass, the difference in the thickness at the crown and at the face joint, the composition of the metal of which the casting is made, and the temperature of the metal when poured into the mould. It should always be allowed for, however, for the following reasons. Referring again to Fig. 2436, it will be noted that it requires a heavy cut off C to bring E, D to a bearing, while it is apparent that if the brass met the box at E, D before it did at C, but little filing at E, D would let the brass down a long way. It saves work, therefore, to so make the pattern as to insure that the brass casting shall have bedding contact at D and E before it does at C. As an example of the allowance to be made for this purpose, it may be stated that in brasses of 6 inches bore and 9 inches long, the hexagon of the brass pattern at D, E, Fig. 2436, would require about 1/16 inch put on them to compensate for the contraction, supposing that the hexagon on the brass pattern were made at first to fit the hexagon of the pedestal or axle box.

To originate a true flat surface we proceed as follows: In the absence of a standard plate to go by, we must have three plates, and one of them must be accepted as a provisional or temporary standard. This we will call No. 1, and we fit Nos. 2 and 3 to it and then try them together, and if they also fit it is proof that No. 1 was true, and that all three are therefore true. It will very rarely happen, however, that this is the case; but Nos. 2 and 3 merely serve to show how much No. 1 was out of true.

Suppose, for example, that No. 1 is concave in its length, and we fit No. 2 to it, as in Fig. 2438, and then fit No. 3 to it as in Fig. 2439, and when we come to put Nos. 2 and 3 together, as in Fig. 2440, we find that they are out of true to twice the amount that No. 1 is, and that all the work that has been done to them to fit them to No. 1 has been thrown away, and possibly to make them worse instead of better. It becomes important therefore to select the most true plate for No. 1, and this we may do as follows:--