The method of aligning the lathe heads at the Pratt and Whitney Company’s workshops is as follows: Fig. 2579 is a side and an end view of a part of a lathe shears a, with the tailstock b thereon. To the bore of the tailstock there is closely fitted an arbor c, accurately turned in the lathe, and having at the end d and at e two short sections of enlarged diameter. A plate f is fitted to the inside Vs of the shears (upon which Vs the tailstock sits). This plate carries a stand g, and a second gauge or stand g. Stand g fits at its foot into a V provided in f, as shown, the object of which is to so hold g to f that its (g′s) face will stand parallel to arbor c. The stand is so adjusted that a piece i may be placed between c and g and just have contact with both, and it is obvious that if this is found to be the case with the tailstock and the stand placed at any position along the bed, the arbor c, and, therefore, the bore of the tailstock, must be true, sideways, to the inside Vs of the lathe shears. The testing, however, is made at the enlarged sections d and e, g of course being firmly bolted to f. To test the height of the arbor c from the Vs, and the parallelism in that direction, stand h is provided. It carries a pointer or feeler k, whose end is adjusted to just touch the enlarged sections d and e of c, it being obvious that when the degree of contact is equal at these two sections, with the tailstock and the plate f moved to various positions along the bed, the adjustment or alignment in that direction is also correct. The adjustment and corrections may then be made with the headstock of the lathe in place of the tailstock, the arbor fitting into the bored boxes of the lathe and extending from it, and having two sections of the same diameter, as sections e in the figure. Now, suppose that in the test thus made the bar c proves to stand true in some locations, but not in others, upon the bed; then it is proof that it is the Vs that require correction, while the tailstock is in error in all cases in which the error is constant, with the tailblock moved in various positions along the shears.
In some practice the heads are bored after being fitted to the ways, and in this case the boring bar may be supported by standards fitting to the lathe bed, running in bearings, and not on centres. There should be three of these bearings, one at one end of the head, and as close to it as convenient, another at the other end, as close as will permit the insertion of the cutters, and the third as far from the second as will permit the insertion on the bar and between them of a pulley to drive the bar, which must be splined to receive a feather in the pulley, so that the bar may be fed through its bearings and through the pulley to the cut. After the live head has been bored the tailstock or back-head may be bored from the other end of the bar, so that the standards will not require to be moved on the bed until the boring is completed. The bar may be fed by hand, or an automatic feed motion may be affixed to one of the standards. The heads being secured to the bed while being bored, there is no liability of error in their alignment, because, even if the holding bolts spring the heads in clamping them to the bed, the holes will be true when the heads are firmly home upon the bed, as they will be when in use, whereas under this condition such will not be the case if the holes for the spindles are bored before the seats are planed and fitted.
The feed screw must be placed quite parallel to the Vs or guides of the bed, or otherwise the pitches of threads cut in the lathe will be finer than they should be, and the screw will bind in the feed nut, causing undue wear to both.
The method employed to test the truth of lathe shears and heads in the David W. Pond Works, at Worcester, Massachusetts, is as follows:—
The planing, both of the lathe shears and of the heads, being done as accurately as possible, the heads are provided with a mandrel or arbor, to the end of which is secured the device shown in Fig. 2580, in which a is a hollow cylindrical piece having a threaded and split end, so that by means of a nut the bore may be closed to tightly fit the arbor referred to; b, b are two arms, a sliding fit in a, to enable their adjustment for the width of lathe Vs, and having a flat place on one side, as at c c, to receive the pressure of a locking device d, by means of which b, b may be fastened in their adjusted positions; e, e are cylindrical arms, a sliding fit in b, b, also having flat sides, and capable of being secured in their adjusted positions by means of locking devices f, f.
Fig. 2581 is an end view of the device in position on a lathe tail stock, and Fig. 2582 is an enlarged view (being half full size) of the devices at the lower end of arms or rods e, e.
At the lower ends of e, e are provided two pieces g, g, which are capable of adjustment to fit the Vs h, h of the lathe, as follows:—
The middle pins i are fast in the arms j, but are pivoted in g, the end pins, as k, are pivoted in g, are flat where they pass through j, and threaded to receive the nuts, l, of which there are four, two to each piece g. By operating these nuts, g may be adjusted to bed fair on the angles on the lathe Vs h. At m are two fixed pins which afford a fulcrum, at n and o respectively, to four index needle arms. Two of these index arms only are seen in the cut, marked respectively p and q, which are pivoted at n. Two similar pointer or needle arms are on the other side of m, being behind p and q, these two being pivoted respectively at o. At the lower end of p is a point resting in the centre of the nut, and similarly the end of q rests in the centre of the nut on that side. Similarly the two needles not seen have pointed ends resting in the centre of the nuts marked respectively l. Between g and j are two springs placed back to back, which act to hold g away from j. But it will be seen that if either end of g be forced towards j, as by passing over a projection on the V h, then the pin k, will push nut l, and this will raise the end of the pointer or needle to a corresponding degree, and the pointer being pivoted (as at n), its upper end will move and denote on the graduated index r that there is an error in the lathe V, the amount of the error being shown multiplied on account of the leverage of the needle arms from the pivots.
The pieces g being adjusted to bed fairly on the lathe Vs, the heads of the lathe are moved along the lathe shears, and if the Vs are true to angle the upper ends of the needles will remain stationary, a projecting part of a V will, however, cause the needle point to move toward e, while a depression on a V would cause the springs k to move g in, keeping it in contact with the V, while the needle point would move away from e. To maintain the needle arms in contact with the nut heads l, springs s are employed. Variations in the widths apart of the Vs on either side of the shears would obviously be shown in the same manner, the defect being located by the needle movement. The corrections are made from the contact marks of the heads, caused by moving the heads along the Vs and by careful scraping.
Notwithstanding that every care and attention may be taken to make a lathe true in the process of manufacture, yet when the whole of the parts are assembled it is found essential to test the truth of the finished lathe, because, by the multiplication of minute errors the alignment of the lathe, as a whole, may be found to need correction. A special inspector is therefore employed to test finished machines before they leave the works, and in Fig. 2583 is represented the device employed for testing the alignment of the line of centres of lathes.
Upon the face of the face plate and near its perimeter there are turned up two steps, as denoted by b and c. The tail-spindle is provided with a stud s, which fits in the place of the dead centre, and carries what may be termed a double socket, one-half of which (as f) envelops the stud s, while the other half (a) envelops and carries a rod r. These two halves are in reality split sleeves, with set screws to close them and adjust the fit. By means of the screws e, the sleeve f may be made a tight working fit upon s, while, by means of screws g, sleeve a may be made to firmly grip the rod r, which may thus be securely held while still capable of being swung upon stud s. Upon the outer end of the rod r is another sleeve i, which is also split and secured to the rod r by means of screws corresponding to those shown at g. It also carries a pin, upon which a disk k is pivoted, and a lug through which the adjusting screw v is threaded. Upon k is a lug which has on one side of it the end of a spring t, and it is obvious that by operating v the disk k will be rotated upon its central pin. k carries two lugs, l and m, the latter being threaded and split. These two lugs receive a sleeve n, threaded into m, and a close plain fit in l. The small end of this sleeve is split and is threaded slightly taper, and is provided with the nut p. Through this sleeve passes a needle q q, one end of which is bent as shown, and it is obvious that by screwing nut p upon n the sleeve will be closed and will tightly grip the needle q q. Now, suppose that the head of n is operated, and it will move endwise through l and m, carrying with it the needle q q, which will remain firmly clasped in the sleeve; or suppose that screw v is operated, and k will revolve, carrying with it the needle q q, which will still remain firmly gripped, and it follows that there is thus obtained a simple means of adjusting the needle without releasing it.
The application of the instrument is as follows: To test if the head and tailstocks are of equal height from the bed, the instrument is set and adjusted exactly as shown in the engraving, the needle being adjusted to just touch the diameter of the step at b. The rod r is then swung around so that the needle comes opposite to the same step b at the bottom of the face plate, and if the needle just touches there also the adjustment for tailstock height is correct. Similarly for testing if the tailstock is set true sideways the needle may be tried in the same manner and upon the same step, but upon the two opposite sides of the face plate, instead of at the top and bottom. It now remains to test if the tailstock is in line in a horizontal direction with the live spindle, and this is done by reversing the needle end for end in the sleeve n, and setting it to just touch the face c of the turned step on the face plate, and if it just touches at the top and bottom as well as at the two sides the tail-spindle is obviously in line. It may be observed, however, that if an error in any one direction is found, it is necessary to go through the whole series of tests in order to precisely locate the error. Suppose, for example, that the needle, being adjusted as in the engraving to just touch the step at b, does not touch it when tried at the bottom of the plate, then the error may be caused in three ways—thus, in the first place, the whole tailstock may be lower than the headstock; in the second place, the front end of the tailstock may be too low; or, in the third place, the back end of the tailstock may be too high. If the first was the cause, the test with the needle point tried with face c would show correct. If the second or third was the cause of the error, the needle point when tried to face c would touch when applied at the top, but would not touch when tried at the bottom of the face plate. Another case may be cited. For example, suppose the needle applied as shown touched at the bottom but not at the top of the step b, then the test with the needle reversed would show whether the whole tailstock was too high, or whether the front end only was too high, or the back end too low. There is one excellent feature in this device to which attention may be called, which is that the tests are made on as large a diameter of face plate as possible, which shows the errors magnified as much as possible.
The same device is used to test if the cross slide of the carriage or saddle is at a right angle to the lathe shears, the method of its application being as shown in Fig. 2584. The split sleeve a receives in this case a rod r, which is laid in the slideway s of the carriage or saddle, and a long rod h carries the needle-holding devices. The rod r is held fair against the slideway, and the face of the sleeve a is held against the edge of the carriage or saddle. The needle q is then adjusted to just touch the edge d of the lathe bed. When this adjustment is made the rod h is swung over to the right and the coincidence of the needle point again tried with the edge of the lathe bed, the cross slideway being at a right angle when the needle point touches the edge d of the lathe bed when tried on the left hand, and also on the right hand, of the carriage. The stiffening rod u is brought under tension by a nut operated against a lug on x. To counterbalance the overhanging weight of the rod h and its attachments, a rod carrying a weight w is employed. It is obvious that the truth of the operation depends wholly upon the straightness and parallelism of the enlarged sections p of the rod r, upon keeping the end face of a in contact with the carriage at z, and upon the correct adjustment of the needle to the edge of the lathe bed.
Setting Line Shafting in Line.—The following method of adjusting line shafting or setting it in line, as it is termed, is that generally adopted in the best practice.
First prepare a number of rude wooden frames, such as shown in Fig. 2585. They are called targets, and are pieces of wood nailed together, with the outer edge face a planed true, and having a line marked parallel with the planed edge and about three-quarters of an inch inside of it. Upon this frame we hang a line suspending a weight and forming a plumb-line, and it follows that when the target is so held that the plumb-line falls exactly over and even all the way down with the scribed line, the planed face a, Fig. 2586, will stand vertical. To facilitate this adjustment, we cut a small V notch at the top of the scribed line, the bottom of the V falling exactly even with the scribed line, so that it will guide the top of the plumb-line even with the scribed line at the top; hence the eye need only be directed to causing the two lines to coincide at the bottom. To insure accuracy, the planed edge a should not be less than a foot in length. Then tightly stretch a strong closely-twisted and fine line of cord beside the line of shafting, as shown in Fig. 2587, placing it say six inches below and four inches on one side of the line of shafting, and equidistant at each end from the axial line of the same, adjusting it at the same time as nearly horizontally level as the eye will direct when standing on the floor at some little distance off and sighting it with the line shaft.
In stretching and adjusting this line, however, we have the following considerations:—It must clear the largest pulley hub on the line of shafting, those pulleys having set-screws being moved to allow it to pass. If the whole line of shafting is parallel in diameter, we set the line equidistant from the shafting at each end. If one end of the shafting is of larger diameter, we set the line farther from the surface of the shafting, at the small end, to an amount equal to one-half of the difference in the two diameters; and since the line is sufficiently far from the shafting to clear the largest hub thereon, it makes, so far as stretching the line is concerned, no difference of what diameter the middle sections of shafting may be. The line should, however, be set true as indicated by a spirit-level.
We may now proceed to erect the targets as follows: The planed edge a in Fig. 2585 is brought true with the stretched line, and is adjusted so that the plumb-line b in Fig. 2586 will stand true with the line or mark b. When so adjusted, the target is nailed to the post carrying the shafting hanger. In performing this nailing, two nails may be slightly inserted so as to sustain the target, and the adjustment being made by tapping the target with the hammer, the nails may be driven home, the operator taking care that driving the nails does not alter the adjustment.
In Fig. 2588 a a represents the line of shafting, b, b two of the hanger posts, and c, c two of the adjusted targets.
We have now in the planed edges a of the targets a rigid substitute for the stretched line, forming a guide for the horizontal adjustment, and to provide a guide for the vertical adjustment we take a wooden straight-edge long enough to reach from one post to another. Then beginning at one end of the shafting, we place the flat side of the straight-edge against the planed edge of two targets at a distance of about 15 inches below the top of the shafting; and after levelling the straight-edge with a spirit-level, we mark (even with the edge of the straight-edge) a line on the planed edge of each target, and we then move the straight-edge to the next pair of targets, and place the edge even with the mark already made on the second target. We then level the straightedge with a spirit-level, and mark a line on the third target, continuing the process until we have marked a straight and horizontally level line across all the targets, the operation being shown in Fig. 2589, in which a represents the line of shafting, b the hangers, and c the targets. d represents the line on the first target, and e the line on second. f is the straightedge, levelled ready to form a guide whereby the line d may be carried forward, as at e, level and straight, to the third target, and so on across all the targets.
The line thus marked is the standard whereby the shafting is to be adjusted vertically; and for the purpose of this adjustment, we must take a piece of wood, or a square, such as is shown in Fig. 2590, the edges a and b being true and at a right angle to each other. The line d, in Fig. 2589, marked across the targets being 15 inches below the centre line of the shaft at the end from which it was started, we mark upon our piece of wood the line c in Fig. 2590, 15 inches from the edge a (as denoted by the dotted line); and it is evident that we have only to adjust our shaft for vertical height so that, the gauge being applied at each target in the manner shown in Fig. 2591, the shaft will be set exactly true, when the mark c on the piece of wood comes exactly fair with the lines d marked on the targets.
For horizontal adjustment, all we have to do is to place a straight-edge along the planed face of the target, and adjust the shaft equidistant from the straight-edge, as shown in Fig. 2592, in which a is the shaft, b the target, c the straight-edge referred to, and d a gauge or distance piece. If, then, we apply the straight-edge and wood gauge to every target, and to the adjustment, the whole line of shafting will be complete.
There are several points, however, during the latter part of the process at which consideration is required. Thus, after the horizontal line, marked on the targets by the straight-edge and used for the vertical adjustment, has been struck on all the targets, the distance from the centre of the shafting to that line should be measured at each end of the shafting, and if it is found to be equal, we may proceed with the adjustment; but if, on the other hand, it is not found to be equal, we must determine whether it will be well to lift one end of the shaft and lower the other, or make the whole adjustment at one end by lifting or lowering it, as the case may be. In coming to this determination we must bear in mind what effect it will have on the various belts, in making them too long or too short; and when a decision is reached, we must mark the line c, in Fig. 2590, on the gauge accordingly, and not at the distance represented in our example by the 15 inches.
The method of adjustment thus pursued possesses the advantage that it shows how much the whole line of shafting is out of true before any adjustment is made, and that without entailing any great trouble in ascertaining it; so that, in making the adjustment, the operator acts intelligently and does not commence at one end utterly ignorant of where the adjustment is going to lead him to when he arrives at the other.
Then, again, it is a very correct method, nor does it make any difference if the shafting has sections of different diameters or not, for in that case we have but to measure the diameter of the shafting, and mark the adjusting line, represented in our example by c, in Fig. 2590, accordingly, and when the adjustment is complete, the centre line of the whole length of the line of shafting will be true and level. This is not necessarily the case, if the diameter of the shafting varies and a spirit-level is used directly upon the shafting itself.
In further explanation, however, it may be well to illustrate the method of applying the gauge shown in Fig. 2590, and the straight-edge c and gauge d shown in Fig. 2592, in cases where there are in the same line sections of shaftings of different diameters. Suppose, then, that the line of shafting in our example has a mid-section of 21⁄4 inches diameter, and is 2 inches at one, and 21⁄2 inches in diameter at the other end: all we have to do is to mark on the gauge, shown in Fig. 2590, two extra lines, denoted in figure by d and f. If the line c was at the proper distance from a for the section of 21⁄4 inches in diameter, then the line d will be at the proper distance for the section of 2 inches, and e at the proper distance for the section of 21⁄2 inches in diameter; the distance between c and d, and also between c and f, being 1⁄8 inch, in other words, half the amount of the difference in diameters.
In like manner for the horizontal adjustment, the gauge piece shown at d in Fig. 2592 would require when measuring the 21⁄4 inch section to be 1⁄8 inch shorter than for the 2 inch section, while for the 21⁄2 inch section would require to be 1⁄8 inch shorter than that used for the 21⁄4 inch section, the difference again being one-half the amount of the variation in the respective diameters. Thus the whole process is simple, easy of accomplishment, and very accurate.
If the line of shafting is suspended from the joists of a ceiling instead of from uprights, the method of procedure is the same, the forms of the targets being varied to suit the conditions. The process only requires that the faced edges of the targets shall all stand plumb and true with the stretched line. It will be noted that it is of no consequence how long the stretched line is, since its sag does not in any manner disturb the correct adjustment, but in cases where it is a very long one it may be necessary to place pins that will prevent it from swaying by reason of air currents or from jarring.
The same system may be employed for setting the shafting hangers, the bores of the boxes being used instead of the shafting itself.
Line shafting.—A line of shafting is one continuous run or length composed of lengths joined together by couplings. The main line of shafting is that which receives the power from the engine or other motor, and distributes it to other lines of shafting, or to the various machines to be driven. In some practice each line of shafting is driven by a separate engine or motor, so that it may be stopped without stopping the others. This same object may be obtained by providing a clutch for each line. It is obvious that in each line of shafting the length nearest to the driving motor transmits the whole of the power transmitted by the line, and that the diameter of the shafting may, therefore, be reduced as it proceeds from the engine in a proportion depending upon the degree to which the power it is required to transmit is reduced. It is desirable, therefore, so far as the shafting is concerned, to place the machines requiring the most power to drive as near as possible to that end of the shafting that receives power from the motor. Line shafting is supported in bearings provided in what are termed hangers, which are brackets to be bolted to either suitable framing, to walls, posts, or to the ceiling or floor of the building. The short lengths of shafting that are provided to effect changes of speed, and to enable the machine to be stopped or started at pleasure, are termed countershafts. When there is interposed a countershaft between the motor and the main line of shafting, it is sometimes termed a jack shaft.
Shafting is usually made cylindrically true either by special rolling processes as in what is known as “cold-rolled,” or “hot-rolled” shafting, or else it is turned up in the lathe. In either case it is termed bright shafting. What is known as black shafting is simply bars of iron rolled by the ordinary process and made cylindrically true only where it receives its couplings, and for its journal bearings, &c. The diameter of black shafting varies by a quarter of an inch, and is usually above its designated diameter by about 1⁄32 inch.
The main body of the shafting not being turned cylindrically true and parallel, the positions of the pulleys cannot be altered upon the shafts, nor can pulleys be added to the shaft as occasion may require without the sections being taken down and seatings turned for the required pulleys to be added. Furthermore black shafting does not run true, and is in this respect also objectionable. Nevertheless, black shafting is used for some special cases where extra pulleys are not likely to be required and the shafting is exposed to the weather, as in the case of yards for the manufacture of building bricks.
The diameters of bright or turned shafting (which is the ordinary form in which shafting is made, unless otherwise specified) vary by 1⁄4 inch up to about 31⁄2 inches in diameter; but the actual diameter is 1⁄16 inch less than the denominated commercial diameter, which is designated from the diameter of the round bar iron from which the shafting is turned; thus a length of what is known as 2-inch shafting will have an actual diameter of 115⁄16 inches, being parallel, or as nearly parallel as it is practicable to turn it in the ordinary lathe.
Cold-rolled shafting has its actual diameter agreeing with its designated or commercial diameter, and is parallel throughout its length.
In England the diameters of shafting vary by eighths of inches for diameters of an inch and less, and by quarters of an inch for diameters above an inch, the commercial and the actual diameters being alike.
The strains to which a line of shafting is subject are as follows: The torsional strain due to rotating the line of shafting, independent of the power transmitted; the torsional strain due to the amount of the power transmitted; and the transverse strain due to the unequal belt pressures and distances from the bearings of the driving or transmitting pulleys. The first and the last are, however, so intimately connected in practice that they may be considered as one: hence we have, 1st, the torsional strain due to driving the whole load, and, 2nd, the transverse strain due to the belt pressures being exerted more on one side than on another of the shaft, and to the belt pulleys being at unequal distances from the hanger bearings.
The first may be reduced to a minimum by so proportioning the strength of the line of shafting that it shall be capable of transmitting the required amount of power at the various sections of its length without suffering distortion of straightness beyond certain limits, and shall be at the same time as light as is consistent with this duty and a certain factor of safety.
Referring for a moment to the above limitation, the weight of the shaft itself will cause it to deflect between the hanger bearings, and the amount of this deflection will depend upon the distance apart of the points of support, or, in other words, of the distance apart of the hanger bearings.
The second may be reduced to a minimum by so regulating the distance apart of the hanger bearings that the deflection of the shaft from the belt pressures shall not be sufficient to produce sensible irregularities in the axis of rotation of the shaft; by so connecting the bearings to the hangers that they shall be rigidly held, and yet capable as far as possible of automatically adjusting their bores to be true with the shaft axis, notwithstanding its deflection from any cause; by placing the pulleys transmitting the most power as near to the hanger bearings as practicable; by so disposing the driving belts as to deliver the power as near as possible equally on all sides of the shaft; and by having the shafting and the pulleys balanced so as to run true, so that the strains on the pulleys shall be equal at each point in the shaft rotation. From this it appears that the distance apart of the shafting hangers may vary according to the amount of power transmitted by a shaft of a given diameter. The following table (given by Francis) gives the greatest admissible distances between the bearings of continuous shafts subject to no transverse strain except from their own weight, as would be the case were the power given off from the shaft equally on all sides, and at an equal distance from the hanger bearing.
| Diameter of shaft in inches. |
Distance between bearings, in feet. | |
| Wrought-iron shafts. | Steel shafts. | |
| 2 | 15.46 | 15.89 |
| 3 | 17.70 | 18.19 |
| 4 | 19.48 | 20.02 |
| 5 | 20.99 | 21.57 |
| 6 | 22.30 | 22.92 |
| 7 | 23.48 | 24.13 |
| 8 | 24.55 | 25.23 |
| 9 | 25.53 | 26.24 |
These conditions, however, do not usually obtain in the transmission of power by belts and pulleys, and the varying circumstances of each case render it impracticable to give any rule which would be of value for universal application.
For example, the theoretical requirements would demand that the bearings be nearer together on those sections of shafting where most power is delivered from the shaft, while considerations as to the location and desired contiguity of the driven machines may render it impracticable to separate the driving pulleys by the intervention of a hanger at the theoretically required location. The nearer together the bearings the less the deflection either from the shaft’s weight or from the belt stress, and since the friction of the shaft in its bearings is theoretically independent of the journal-bearing area, the closer the bearings the more perfect the theoretical conditions; but since it is impracticable to maintain the true alignment of the shaft, and as the friction due to an error in alignment would increase with the nearer proximity of the bearings, they are usually placed from about 7 to 12 feet apart, according to the facilities afforded in the location in which they are to be erected.
It is to be observed, however, that the nearer together the bearings are the less the diameter, and, therefore, the lighter the shafting may be to transmit a given amount of power, and hence the less the amount of power consumed in rotating the shafting in its bearings.
Cold-rolled Shafting—This is shafting made cylindrically round and parallel by means of cold rolling, which leaves a smooth and bright surface. The effects of cold rolling upon the metal have been determined by Major Wm. Wade, U.S.A., Sir William Fairbairn, C.E., and Professor Thurston, of the Stevens Institute, as follows:—
The experiments were made upon samples of cold-rolled shafting submitted by Messrs. Jones and Laughlins, of Pittsburgh, Pennsylvania.
| Iron rolled while | Ratio of increase by cold rolling. |
Average rate per cent. of increase. |
|||||||||||
| Hot. | Cold. | ||||||||||||
| Transverse.—Bars supported at both ends; load applied in the middle; distance between the supports, 30 inches. Weight which gives a permanent set of one-tenth of an inch, viz. | - | 11⁄2 inch square bars | 3,100 | 10,700 | 3.451 | - | 162 | 1⁄2 | |||||
| Round bars, 2 | inch | diameter | 5,200 | 11,100 | 2.134 | ||||||||
| Round bars, 21⁄4 | „ | „ | 6,800 | 15,600 | 2.294 | ||||||||
| Torsion.—Weight which gives a permanent set of one degree, applied at 25 inches from centre of bars. Round bars, 13⁄4 inch diameter, and 9 inches between the clamps | 750 | 1,725 | 2.300 | 130 | |||||||||
| Compression.—Weight which gives a depression, and a permanent set of one-hundredth of an inch to columns 11⁄2 inches long and 5⁄8 inch diameter | 13,000 | 34,000 | 2.615 | 161 | 1⁄2 | ||||||||
| Weight which bends and gives a permanent set to columns 8 inches long and 3⁄4 inch diameter, viz. | - | Puddled iron | 21,000 | 31,000 | 1.476 | - | 64 | ||||||
| Charcoal bloom iron | 20,500 | 37,000 | 1.804 | ||||||||||
| Tension.—Weight per square inch, which caused rods 3⁄4 inch diameter to stretch and take a permanent set, viz. | - | Puddled iron | 37,250 | 68,427 | 1.837 | - | 95 | ||||||
| Charcoal bloom iron | 42,439 | 87,396 | 2.059 | ||||||||||
| Weight per square inch, at which the same rods broke, viz. | - | Puddled iron | 55,760 | 83,156 | 1.491 | - | 72 | ||||||
| Charcoal bloom iron | 50,927 | 99,293 | 1.950 | ||||||||||
| Hardness.—Weight required to produce equal indentations | 5,000 | 7,500 | 1.500 | 50 | |||||||||
| Note.—Indentations made by equal weights, in the centre, and near the edges of the fresh cut ends of the bars, were equal; showing that the iron was as hard in the centre of the bars as elsewhere. | |||||||||||||
| Condition of bar. | Breaking weight of bar in lbs. |
Breaking weight per square inch. |
Strength, the un- touched bar being unity. |
||
| In lbs. | In tons. | ||||
| 1 | Untouched (black) | 50,346 | 58.628 | 26.173 | 1.000 |
| 3 | Rolled cold | 69,295 | 88.230 | 39.388 | 1.505 |
| 4 | Turned | 47,710 | 60.746 | 27.119 | 1.036 |
| Note.—In the above summary it will be observed that the effect of consolidation by the process of cold rolling is to increase the tensile powers of resistance from 26.17 tons per square inch, to 39.38 tons, being in the ratio of 1:1.5, one-half increase of strength gained by the new process of cold rolling. | |||||
Extract from the general conclusions arrived at by Professor R. Thurston from experiments.
“The process of cold rolling produces a very marked change in the physical properties of the iron thus treated.
“It increases the tenacity from 25 to 40 per cent., and the resistance to transverse stress from 50 to 80 per cent.
“It elevates the elastic limit under torsional as well as tensile and transverse stresses, from 80 to 125 per cent....
“It gives the iron a smooth bright surface, absolutely free from the scale of black oxide unavoidably left when hot rolled.
“It is made exactly to gauge diameter, and for many purposes requires no further preparation.
“The cold-rolled metal resists stresses much more uniformly than does the untreated metal. Irregularities of resistance exhibited by the latter do not appear in the former; this is more particularly true for transverse stress.
“This treatment of iron produces a very important improvement in uniformity of structure, the cold-rolled iron excelling common iron in density from surface to centre, as well as in its uniformity of strength from outside to the middle of the bar.
“This great increase of strength, stiffness, elasticity, and resilience is obtained at the expense of some ductility, which diminishes as the tenacity increases. The modulus of ultimate resilience of the cold-rolled iron is, however, above 50 per cent. of that of the untreated iron.
“Cold-rolled iron thus greatly excels common iron in all cases where the metal is to sustain maximum loads without permanent set or distortion.”
From this it appears that cold-rolled iron is peculiarly adapted for line shafting. Suppose, for example, a given quantity of power to transmit, and that a length of cold-rolled and a length of hot-rolled iron be connected together to form the line. Then the diameters of the two being such as to have equal torsional strength, we have—
1st. That the weight of the cold rolled will be the least, and it will, therefore, produce less friction in the hanger bearings.
2nd. That the cold rolled will be harder, and will therefore suffer less from abrasion of the journals.
3rd. That being of smaller diameter the journals are more easily and perfectly lubricated.
The resistance to transverse stress (say) 50 per cent.; but the elastic limit under transverse stress is increased from 80 to 125 per cent., accepting the lesser amount we have in the case of the two shafts.
4th. That the resistance to permanent set or bend will be 30 per cent. more in the cold rolled.
5th. The accuracy to gauge diameter enables the employment of a coupling having a continuous sleeve, and gives an equal bearing along the entire coupling bore.
6th. The reduction of shaft diameter enables the employment of a smaller and lighter coupling; and
7th. The hubs of the pulleys may be made smaller and lighter, are easier to bore, and may be bored to gauge diameter with the assurance that they will fit the shaft.
The friction between the journals of a line shafting and its bearings depends so intimately upon the distance apart of the bearings, upon the alignment of the same, upon the accurate bedding of the shaft journals to the bearings, and upon the amount of transverse strain; and this latter is so influenced by the amount of power that may be delivered from one side of the shaft more than from another, that the application of rules for determining the said friction under conditions of perfect alignment rigidity would be practically useless. The conditions found in actual practice are so widely divergent and so rarely alike, or even nearly alike, that the consideration of this part of the subject would, in the opinion of the author, be of no practical value. The reader, however, is referred to the remarks made with reference to the friction of journals.
To prevent end motion to a line of shafting it is necessary that there be fixed at some part of the line two shoulders, or collars, on relatively different sides of a bearing, or of the bearings, these collars meeting the side faces of the bearing. If shoulders are produced by reducing the diameter of the journal bearing of the shaft, the strength of the shafting is reduced to that at the reduced bearing, because the strength of the whole can be no greater than its strength at the weakest part. If collars are placed one on each end of the line of shafting, the difficulty is met that the collars will permit end motion to the shaft whenever the temperature of the shaft is greater than that which obtained at the time at which the collars were adjusted, which occurs on account of the increased expansion of the shaft. On the other hand the collars will bind against the side faces of the bearing boxes whenever the shaft is at a lower temperature than it was at the time of setting the shaft, because of the contraction of the shaft’s length, and this would cause undue friction, abrasion, and wear.
It is preferable, therefore, to place such collars one on each side of one bearing, so that the difference in contraction and expansion from varying temperatures shall be confined to the difference in expansion between the metal of which the bearing and shaft respectively are composed in the length of the bearing only, instead of being extended to the difference in expansion between the shaft throughout its whole length and that of the framework to which the hangers, or bearings, are bolted.