Fig. 3043Fig. 3043.
Fig. 3043.
Fig. 3043represents a foot-power hammer or Oliver. The hammer is upon a shaft in bearings, and is held in the position shown by an open coiled spring. On the shaft is a chain pulley, the other end of the chain being connected through a leather strap to the treadle. Means are provided to adjust the height to which the hammer will lift to bring the hammer face fair with the work and to give the required degree of tension to the spring.
Fig. 3044Fig. 3044.
Fig. 3044.
Fig. 3044represents a Standish’s foot-power hammer, in which the hammer and the anvil are provided with dovetail seats for receiving dies, swages, &c. The force of the blow is regulated by the height to which the hammer is raised, which may be adjusted by the nuts beneath the spiral springs. The handle on the hammer is for pulling the hammer down by hand when adjusting the lower die fair with the upper one.
What are known as power hammers are those driven by belt and pulley; while those known as trip hammers have their helve lifted through the medium of revolving lugs or cams. Steam hammers are those in which the hammer is lifted by a piston in a steam cylinder; while in hydraulic hammers, the hammer is moved by water pressure.
Fig. 3045Fig. 3045.
Fig. 3045.
Fig. 3045represents a Justice’s power hammer, in which the hammer is guided in a slideway and is operated by leather straps attached to the ends of a spring, at the crown of which is attached a connecting rod driven by a crank disk. The stroke is altered by means of placing the crank pin in the required position in the slot in the crank disk. By means of gibs the hammer may be set to match the dies. The pulley is provided with a friction clutch operated by the treadle, shown.
Fig. 3046Fig. 3046.
Fig. 3046.
Fig. 3046represents a Bradley’s Cushioned Hammer, in which motion is obtained by a belt passing over a pulley on a crank shaft, whose connecting rodris capable of adjustment for length, so as to govern the distance to which the hammer shall fall, which obviously varies with different sizes of work. The hammer is lifted through the medium of a rubber cushiona, seated in a casting to one end of which is connected the rodr, while the other end is pivoted. The lever to which the hammer is affixed is raised against the compression of the rubber cushionb, and at the top of its stroke also meets the rubber cushionc; hence these two cushions accelerate its motion after the crank has passed its highest point of revolution. The cushiondprevents the rebound of the hammer after the blow is struck; hence as a result of these cushions, heavy or light blows may be struck with great rapidity and regularity. The weightwis on a lever that actuates a break upon the wheel shown at the side, so as to enable the stopping of the hammer quickly. The machine is put in motion by pressing the foot upon the treadlet, whichoperates a belt tightener, the belt running loose when the treadle is released.
The hammer lever or helve is adjustable for height by means of the screwgand hand-wheelh, which raise or lower the bearings in which the helve journals are carried. This is necessary, because as the helve moves in the arc of a circle the faces of the upper and lower die, or of the hammer and the anvil, as the case may be, can only come fair at one particular point in the path of the hammer; hence in proportion as the blow terminates (by meeting the work surface) farther from the anvil face, the pivot or journal of the helve must be raised, so that the journal will be horizontally level (or as nearly so as possible) with the hammer face at the moment the blow is delivered.
By giving motion to the helve through the medium of cushions, a direct mechanical connection, and the destructive concussion that would accompany the same, is avoided; hence a high speed may be obtained without the frequent breakage that would otherwise ensue.
Fig. 3047Fig. 3047.
Fig. 3047.
Fig. 3047represents Corr’s power hammer, the construction being as follows: The semi-elliptic springs, shown on top and bottom of the beam, serve to balance the stroke, so that the hammer may run from 350 to 450 strokes per minute, with safety to the machinery. The hammer is adapted to almost any form or kind of forging. Large dies may be inserted for various kinds of forming and welding, such as making plough-shares and other articles, which require that the operation be commenced with a light tap, and increased to a heavy blow at the will of the operator.
The whole structure is mounted on a substantial iron bedv, 18 inches deep, 22 inches wide and 51⁄2feet long. Attached to this bedvare two circular armsl; between them is pivoted near their top, atk, an oscillating frameh, having a longitudinal opening, in which is attached two semi-elliptic springsg g, and two platesi, with trunnions projecting laterally through the oscillating frame atk; the hammer beamfis inserted between the springsg g, and the trunnion platesi, which are bolted firmly to beamfati; the ends of the trunnions and outsides of the oscillating framehrest evenly against the inside of the circular armsl; atka shaft is passed through the trunnions and beamf, and made rigid in them with its ends resting in boxing atk. Caps are provided to cover the ends of the boxing and shaft with set-screws projecting against the ends of the shaft, which secures it against end play.
By these mechanical arrangements the beamfand oscillatorhare securely attached independently, vibrating on one common centre, allowing no side play of the hammere, admittingfto the free action of the springsg g; in the lower end of the oscillating frame atnis a lateral opening 10 inches vertically by 6 inches longitudinally and 4 inches laterally, with flanges projecting longitudinally one inch into this opening from both sides. This makes the opening two inches smaller on the outside than the internal cavity; the rear and front internal walls are provided with steel plates, 4 by 10 inches,1⁄4thick, resting against the inner ends of four set-screws, not shown, provided to adjust these plates to or from the sliding box atn, to compensate for wear and prevent lost motion. These plates and flanges form slides and guides between which a loose box and eccentric is provided with shaft projecting laterally through boxing atn, which project upwards from an adjustable frame immediately under the oscillatorh; this permanently locates the eccentric and shaft in the lateral opening in the oscillatorh, atn. The adjustable frame mentioned rests on suitable bearings on the inside of the circular armsl, and is fastened down by four bolts passing through suitable slots in the adjustable frame, entering the bearings on the armsl. This frame is adjusted back or forth by set-screwss s; this adjustment is for the purpose of giving a greater or less distance between the anvil and hammer atd, as may be desired for large or small work, long or short dies, &c.
The anvilb, weighing about 500 lbs., sits down in the bed atrand rests on circular bearings (betweenrandb), which radiate to the centre of the top of the anvil atd, and is held rigidly in any position longitudinally desired by set-screwsq q, with their inner ends resting on shoulders on the sides of the anvilb, which projects down about ten inches; between this lower projection and the internal wall of the bed is sufficient space to admit of any adjustment desired. This lateral adjustment is accomplished by set-screwsr, passing through the sides of the bedv, with their inner ends resting against the anvil which holds it rigid at any lateral adjustment. By this arrangement the anvil is accommodated to all and any class of work or shape of dies.
The anvil is constructed in two parts. Four inches of the topcmay be taken off, leaving a suitable place to insert large dies for various purposes, such as dies for welding plough-shares and dies for forging journals on large shafts. A counter-shaft, provided with suitable pulleys, is attached on the rear end of the bed; this shaft is kept constantly in speed and power by the vertical belt in the direction indicated by the arrow; the other end of the shaft is provided with a flanged pulley, corresponding to a flanged pulleym, on the eccentric shaft; around these pulleys is placed a loose belt, as shown; in contact with this is a press pulleyt, adjustably attached by two arms to the projecting end of the treadlepato. If the foot be placed on the treadle atuand it be pressed down, the break on the opposite side breaks contact with the balance wheel (not shown); the press pulley will at the same time tighten the loose belt on the flanged pulleys. This gives motion to the pulleym, in the direction indicated by the arrow. Its motion is increased by a heavier pressure until it attains the same speed as the other flanged pulley; this would be the full speed, which maybe diminished to any speed desired by lessening the pressure on the loose belt. By this means motion and power is given to the eccentric, which carries back and forth the lower end of the oscillating frameh; this gives vertical motion to the springsg g, and this imparts corresponding motion to the beamf. These springs accomplish a threefold object:
1st. They carry the hammereup and down.
2nd. They cushion the hammer at the returning points and give off that power which was stored in them while cushioning.
3rd. By the power exerted in the machinery they follow up and impart still greater force to the blow.
It is found by this arrangement of eccentric loose box and oscillator that when the machinery is moved in the direction indicated by the arrow, that the downward stroke is one-sixth quicker than the up stroke; this is a natural result, for the down stroke is performed while the eccentric is revolving above the centre of its shaft and nearest the fulcrum of the operatorh. With the present arrangement the downward stroke is performed with5⁄12of the revolution and the up stroke is performed with7⁄12; the difference is2⁄12, which equals one-sixth. The up stroke is performed while the eccentric is revolving below the centre of its shaft and in that part farthest from the fulcrum of the oscillatorh, so if the machinery were reversed the quick stroke would be up and the slow stroke would be down.
Largeimage(164 kB).Fig. 3048Fig. 3048.
Largeimage(164 kB).
Fig. 3048.
InFig. 3048is shown a Kingsley’s trip hammer. The main bed or foundation plateacarries the bed plate or frameb, at one end of which are the pillar blocksc, which afford journal bearing to the casting carrying the hammer shafte, being fastened thereto by the clampd. These journals are the centre of motion of the hammer helvee.
At the other end of the bed plateb, are the pillar blocksf, affording journal bearing to the cam and fly-wheel shaft,a′′is the tripping cam, which is provided with two toes or cam arms, which meet the tripping pieceb′′, and this gives the hammer two strokes in a revolution of the fly-wheel shaft or cam shaftg. The stroke of the hammer may be altered by means of the set-screwsc′′, which move the pillar blocksf, so that the cam toesa′′have contact with the tripping pieceb′′through more or less of the revolution ofa′′; the pillar blocksfbeing retained in their adjusted position by means of the set-screws shown below them in the bed pieceb.
By the following means provision is made whereby the face of the hammer may be set out of parallel with that of the anvil block or lower died′.
Fig. 3049Fig. 3049.
Fig. 3049.
Fig. 3049is a sectional view through the pillar blocksc, and casting and clampd. The pillar blocksc care carried in a semicircular framea′, hence by unscrewing the boltsb′and screwing up the pillar block on the other side, the journals are thrown out of parallel, and the plane of motion of the hammershaft is altered so that the face of the upper die does not meet that of the anvil die fair to an amount which may be varied at will by operating the screwsb′. The object of this is to enable the forging taper (as in sword blades) with common dies, and thus to save the making of special dies for each degree of taper required.
Similar provision is made in the anvil block which is easier to set, providing the degree of taper is within the limit of its range, of movement, otherwise the hammer also may be set.
Fig. 3050Fig. 3050.
Fig. 3050.
Fig. 3051Fig. 3051.
Fig. 3051.
Fig. 3050represents a drop hammer, andFig. 3051is a sectional view of the lifting mechanism.
This machine consists of a base or anvil, a hammer which moves up and down between two uprights, and a lifting device, which is secured to the top of the uprights.
A board secured to the hammer passes up between two friction rolls, which revolve in opposite directions. When the two rolls are moved towards each other, the friction on the board causes the hammer to rise; and when again separated the hammer will fall. Thebackroll is keyed to a shaft, on each end of which is a driving-pulley; and thus by the use of two pulleys on the same shaft, equal wear comes on the bearings in which it revolves. Thefrontroll turns freely on its shaft, and is driven by the back roll being geared to it. To secure to the gears both strength and durability, they are made with wide faces, are geared at both ends, and the teeth are of peculiar shape.
The bearings to the shaft, on which the front roll revolves freely, are eccentric to the roll, and a partial revolution of the shaft moves thefronttowards thebackroll, pinching the board. To an arm which is secured to the front shaft is fastened the upright rod, theupwardmovement of whichopensthe rolls, and whosedownward movement closes the same; the weight of the rod being sufficient to cause the hammer to rise. This arrangement, simple and yet substantial, dispenses with the two eccentric-armed bushings, and the spreading of the upright rod at the top to reach both bushings, which caused so much trouble in the old way. In place of the dog which is usually used to hold up the hammer, (which is limited in adjustment to holes located at fixed distances in one of the uprights, necessitating not only the removal of the dog to another hole, and connecting and disconnecting the same to the treadle, but also the most accurate adjustment of the collar on the upright rod to the dog holding the hammer), we use a pair of clamps, located on the lifter, under the rolls. These clamps, holding the hammer centrally, prevent the side blow against the upright, the inevitable result of the contact of hammer and dog, when the former is only held on one side, as it must be, by the use of the dog. The opening of the clamps by the foot-treadle allows the hammer to fall; and the clamps are so made that the hammer will ascend freely, whether the foot is on the treadle or not, and if the foot is off the treadle, will hold up the hammer at any point where it may be arrested in its upward movement. It will be readily seen that the only adjustment required is that of the collar on the upright rod, to any height of blow desired.
This machine has two treadles, one connected to the clamps, and the other to a lever which operates the upright rod.
To obtain repeated blows with one motion of the foot, place the foot upon the treadle connected to the clamps. If variable blows are wanted, place the foot upon theothertreadle, and the hammer will follow the motion of the foot. This extra treadle is a late improvement, and is not shown in the cut. The operation required to obtain automatically any number of blows of the same height is described asfollows:—
Pressure upon the treadle opens the clamps and allows the hammer to fall; just before the dies come together, the trip at the bottom which holds up the upright rod is released, and allows the rod to drop; this closes the rolls, causing the hammer to ascend. The hammer continues to rise until it strikes the collar on the upright rod, and, lifting the rod, opens the rolls, removing the pressure upon the board, and allows the trip at the bottom to go under to hold the rod up, and the hammer remains suspended, provided the foot is off the treadle. So long as pressure is kepton the treadle, the blows of the hammer will be continuous; but upon removal of the pressure, the hammer will assume its original position.
To procure variable blows, the operation is asfollows:—
Pressure upon the treadle connected to the lever which operates the upright rod communicates itself to the treadle that opens the clamps, and the hammer falls; a locking device (not shown in cut) keeps this treadle down, and on completion of the variable blows wanted, removal of the foot from the treadle disconnects the locking device, and the hammer goes up to its original position, and is there held by the clamps.
When the work is such that the operator requires an assistant, variable blows may be obtained by the use of the hand lever by this assistant.
A gentle pressure upon the treadle will allow the hammer to go down slowly, but it will stop and remain suspended at any point as soon as the pressure is removed. The hammer can also be arrested at any point on its way up, by bringing into action the hand lever, so that the next blow can be given from a state of rest at a less height than the collar is set for. The clamps in holding up the hammer keep the board from touching either roll, and prevent the same from being worn uneven when not in use.
The back roll is made adjustable to different thicknesses of lifting board, as are also the clamps.
Fig. 3052Fig. 3052.
Fig. 3052.
Fig. 3053Fig. 3053.
Fig. 3053.
Largeimage(145 kB).Fig. 3054Fig. 3054.
Largeimage(145 kB).
Fig. 3054.
Largeimage(128 kB).Fig. 3055Fig. 3055.
Fig. 3055.
Fig. 3056Fig. 3056.
Fig. 3056.
Figures from3052to3056represent a steam hammer. The headais set at an angle in the frame. The anvil or diecis oblong, as is also the anvil died. The object of this arrangement is to enable the workman, after drawing out his work across the short way of the die, to turn it and finish it lengthwise without being inconvenienced by the frame. By this means skew andT-shaped dies can be dispensed with, and the full service of the ram utilised. The latter is moved between the guidese e, and held in place by the steel platef, bolted through the frameb. The valvegis a plain cylinder of cast iron, enlarged at each end to work in the cylindrical seatsh h, in which the portsi iare placed. Steam is admitted through the valvej, and circulates round the valveg, between the seats. The exhaust chamberkis below the cylinder, which therefore drains condensed steam into it at each stroke through the lower steam port. The exhaust above the piston passes down through the interior of the valve, as shown by the arrow on the drawing. The valve stemlis connected with the valves in the exhaust chamber. No stuffing box is therefore required, there being only atmospheric pressure on each side of it. This combination enables the valve to be so perfectly balanced that it will drop by its own weight while under steam.
The automatic motion is obtained by an inclined planemupon the rama, which actuates the rockern, the outer arm of which is connected by a link to the valve stem, and thus gives motion to the valve. The valve is caused to rise in the up-stroke by means of the rockernand its connections, through the inclined plane. The steam is thus admitted to the top, which drives down thepiston, while the valve and its connections follow by gravity, thus reducing considerably the friction and wear upon the valves. In very quick work the fall of the valves may be accelerated by the aid of a spring; or it may be retarded in heavy work by friction springs, so as to obtain a heavier blow by a fuller admission of steam. For general work, however, the arrangement shown is perfectly effective, and as the rockernis hung upon the adjustment leverp, any required variation can be obtained by the movement of the lever. Single blows can be struck with any degree of force, or a rapid succession of constant or variable strokes may be given.
The anvilorests upon a separate foundation, in order to reduce the effect of concussion upon the frame. The drawing illustrates the arrangement. The bed is long, extending beyond the hammer on each side so as to give plenty of area, and the ends are left open for convenient access in case the anvil should settle and require re-adjustment.
Other forms of hammers having the same general principles of construction are asfollows:—
Fig. 3057Fig. 3057.
Fig. 3057.
Fig. 3057represents a double frame hammer, the weight of the hammer being supplemented by steam pressure. The spiral springs shown beneath the cylinder are to prevent the hammer from striking the cylinder and causing breakage from careless handling by the operator. The valve gear is arranged for operation either automatically or by hand.
Fig. 3058Fig. 3058.
Fig. 3058.
Fig. 3058represents a double frame steam drop hammer for stamping work out in formers or dies. The frames are bolted to the anvil base and the ram for the top die is guided by vertical slides on the inner face of the frame. Shoes are provided, whereby the wear of the ram and of the slides may be taken up, and the upper die kept properly matched with the lower one.
Fig. 3059Fig. 3059.
Fig. 3059.
Fig. 3059represents a double frame steam drop hammer for locomotive and car axles and truck bars. The frame is spread at the base to admit wide work, and the upper surface of the baseis provided with rollers supported by springs, these rollers supporting the work. The same may be operated automatically or by hand.
The hydraulic forging press at the Edgemore Iron Works of Wilmington, Delaware, consists of a piston operating in a cylinder, and having at its lower end a head guided by four cylindrical columns that secure the base plate, or anvil, as it may be termed, to the cylinder. To the above-mentioned head is secured the upper die, the lower one being secured to the base plate.
Fig. 3060Fig. 3060.
Fig. 3060.
Fig. 3061Fig. 3061.
Fig. 3061.
Fig. 3062Fig. 3062.
Fig. 3062.
Fig. 3060represents a female die, andFig. 3061plan of another female die, andFig. 3062plan of male die used in connection with the press to forge the eye bars for the Brooklyn Bridge, five pieces each an inch thick being welded to the bar and pressed into shape at one operation.
Fig. 3063Fig. 3063.
Fig. 3063.
Fig. 3064Fig. 3064.
Fig. 3064.
Fig. 3065Fig. 3065.
Fig. 3065.
Fig. 3066Fig. 3066.
Fig. 3066.
Figures from3063to3066represent a locomotive driving wheel ready to have its hub welded by hydraulic pressure. The spokes having been forged are held together by a band or hoop, as shown. The thickness of the hub or boss is made up by the rings or washers shown in the sectional view. The dies under which the welding is done are shown inFigs. 3064and3066.
Fig. 3067Fig. 3067.
Fig. 3067.
Thin forgings are often made by compression between two rollers, the form of the surface of the rollers, or projections or depressions upon the same, pressing the forging to shape.
Thus, inFig. 3068are shown a pair of rollsa b,prepresenting a piece of work, andc dtwo cam pieces fast upon the roll surfaces;sis a fixed stop.
Suppose the work to be pushed through the rolls and to rest against the stops, then when the camsc dmeet it they will pullit through and reduce its thickness by compression towards the workman. The rollers are obviously rotated by gear wheels; but they are sometimes provided with a certain amount of give or elasticity at their bearings, so that the reduction of work diameter may be obtained by several passages of the work through the rolls.
Fig. 3068Fig. 3068.
Fig. 3068.
Fig. 3069Fig. 3069.
Fig. 3069.
The shape of the cams, asc d, determines that of the work; thus inFig. 3069is shown a pair of rolls for forming knife blades, each cam having sunk in it a die equal in depth to half the thickness of the knife.
If the work is very short in comparison with the circumference of the rolls, two, three, or more cams may be arranged around the circumference, making an equal number of forgings or impressions, as the case may be, at each revolution of the rolls.
InFig. 3067is shown a nail-forging machine for producing, from strip iron, nails similar to hand-made, at rates varying from two to three hundred per minute, and lengths of from six to one inch, two nails being completed at each revolution of the driving shaft of the machine. The framing consists chiefly of a main casting, to which are fixed an upper frame, carriages for the driving shaft, and other details. The principal moving part is a heavy steel slide, deriving its motion from a crank pin with adjustable throw; this slide carries two shears, two gripping dies, and sundry indispensable appendages, to some of which it imparts motions for guiding the nails between the stages of cutting off and finishing.
The successive operations by which each nail is perfected are asfollows:—
A piece of iron about six inches long, and of a width and thickness respectively of the finished nail, is inserted at a red heat to the feeder of the machine; a narrow strip is immediately cut off the lower side of the heated iron, and by the motion of the steel slide is carried to and pressed against a fixed die; while in this position another die rises at right angles and presses the partially formed nail against another fixed die. Thus the headless nail is firmly held on its four sides, and while in this position a lever, moved by a cam, and carrying a suitable tool, advances and forms the head, thus completing the nail. The return motion of the steel slide releases the nail, leaving it free to fall, but as its weight is not sufficient to insure this happening, a “knocker off” is provided, which at the right moment forcibly ejects the nail by way of a guiding shoot into a receptacle placed outside the machine. It is to be noted that the tools for shearing and gripping, and which have to be changed with each different size of nail, are made of a special mixture of cast iron. They are thus easy of preparation and renewal, while at the same time answering their intended purpose as well as or better than the finest cast steel, at less than half the cost. The whole of the machine is carried upon an open-top cast-iron water tank, serving as a receptacle for the tongs and tools heated in withdrawing the iron from the furnace.
Largeimage(110 kB).Fig. 3070Fig. 3070.
Fig. 3070.
Fig. 3071Fig. 3071.
Fig. 3071.
Figs. 3070and3071represent a machine for forging threads on rods and screws. As forgings, the threads are beautifully clean, and for the general work of coach screws much stronger than the cut threads. A perspective view of the machine is given inFig. 3070, and a vertical of it shown inFig. 3071. In the former figure,a bare the screw dies. The rod or bolt to be threaded is placed upon the lower dieb, and fed forward while screwing it. The upper die is mounted on a slidec, which is actuated in the downward direction by an eccentriceon the main shaft and the toggle-bard, the upward motion being obtained by an internal spiral springf. The lower diebis carried in a slideg, and is adjusted at the proper distance from the upper die by means of wedgeh, and the inclined platei, beneath the slideg. The wedgehis operated by a pedall, and secured in its highest position by a boltj, received in a mortice made in the platei, the bolt being operated by a pedalm. In order to release the wedge and return it to its lowest position, the bolt is raised by pressing down the pedalm, whereby the wedge is free to be returned by the counterweightsk, in connection with pedall; slideg, carrying the lower die, then descends by its own gravity, and so separates the two dies sufficiently to allow of the removal of the screw-bolt or rod therefrom. To compensate for the wear of the dies, and admit of their adjustment, another wedgeo, with screw adjustment, is disposed below the inclined platei.
Fig. 3072Fig. 3072.
Fig. 3072.
Fig. 3072represents a lag screw forged by the machine.
Fig. 3073Fig. 3073.
Fig. 3073.
Fig. 3073represents a finishing machine for horseshoes. Thebars of iron are rolled with the creases (for the nail heads of the finished shoe) in them. The blanks for the shoes are then cut to length and bent, and the nail holes punched. The shoes then pass to a machine,Fig. 3073, which consists of a framea b, carrying the rollc, above the tabled, and a second roll, not shown in the cut, but being directly beneathc, there being between these two rolls sufficient space to let the dies (which press the shoes into shape) pass.
These dies rest upon the tabled, and are carried around upon it in a direction from left to right of the chainh, to the links of which the dies are attached. This chain is operated by the vertical shaftj, having a pulley for belt power atk.
As each die approaches the rollers, a shoe (cut to length, creased, and punched as already described) is placed on it, and on reaching the rolls the shoe is pressed into form on the die by the rolls, the bottom roll serving as a rolling bed so as to reduce the friction that would be due to a sliding motion on the bottom of the die. The top rollc, which presses the shoe into the die is driven by power.
Fig. 3074Fig. 3074.
Fig. 3074.
Fig. 3075Fig. 3075.
Fig. 3075.
A plan view of the machine is shown inFig. 3074, and a view showing the shape of the dies is given inFig. 3075.
Fig. 3076Fig. 3076.
Fig. 3076.
The surfacehforms the frog. To give the required concavity to the toe and sides of the shoe, the surfaceiis made convex, and tapered or inclined towardsh. The treadeis deepest at the heel on both sides, and highest at the toe. It is obvious that by suitably shaping the surfacesh,i, ande, any required form may be given to the shoe.Fig. 3076represents a shoe creased, punched, and bent ready to be passed to the machine.
Fig. 3077Fig. 3077.
Fig. 3077.
Fig. 3077represents a circular saw for cutting off hot iron;ais the frame of the machine, the armbpivoted atccarrying the sawd;fis a spring bolted to the frame and serving to hold the saw in the position shown. The workeis gripped by the leverl, which is pushed over by hand. The leverlis adjusted to suit different sizes of work by the screwg, which raises or lowers the pieceh, to whichlis pivoted. The saw is brought into contact with the work, and fed to it by applying the foot to the lever or armbati, the screwjbeing made to contact with the foot of the machine by the time the saw has passed through the work, thus preventing the saw from moving too far forward after passing through the work.
Pattern-making.—Of the different kinds of wood serviceable to the pattern-maker, pine is, for many reasons, usually employed. It should be of the best quality, straight-grained, and free from knots; it is then easy to work in any direction, possessing at the same time sufficient strength for all but the most delicate kinds of work, and having besides the quality of cheapness to recommend it. Care taken in its selection at the lumber-yard will be amply repaid in the workshop. When it is straight-grained, the marks left by the saw will show an even roughness throughout the whole length of the plank; and the rougher the appearance, the softer the plank. That which is sawn comparatively smooth will be found hard and troublesome to work. If the plank has an uneven appearance—that is to say, if it is rough in some parts and smooth in others—the grain is crooked. Such timber is known to the trade as cat-faced. In planing it the grain tears up, and a nice smooth surface cannot be obtained. Before purchasing timber, it is well to note what convenience the yard possesses for storing. Lumber on the pile, though it be out in all weathers, does not deteriorate, but becomes seasoned; nevertheless its value is much increased if it has an extemporised roof to protect it from the sun and rain. But as it is not convenient to visit the pile for every customer, quantities are usually taken down to await sale, and for such a shelter must be provided, otherwise it will be impossible to insure that the lumber is dry, sound, and fit for pattern-making. It is obvious that the foregoing remarks on the storage of lumber apply to all woods.
The superiority of pine for pattern-making is not, however, maintained when we come to fine delicate patterns or patterns requiring great durability. When patterns for fine work, from which a great many castings are to be made, are required, a fine pattern wherefrom to cast an iron pattern is improvised, because, if pine were employed, it would not only become rapidly worn out, but would soon warp and become useless. It is true that a pine pattern will straighten more easily than one made of a hard wood; but its sphere of usefulness in fine patterns is, for the above reasons, somewhat limited. Iron patterns are very desirable on account of their durability, and because they leave the sand easily and cleanly, and because they not only do not warp but are also less liable than wooden ones to give way to the sand, while the latter is being rammed around them by the moulder, a defect that is often experienced with light patterns, especially if they are made of pine. Iron patterns, however, are expensive things to make, and therefore it is that mahogany is extensively employed for fine or durable pattern work. Other woods are sometimes employed, because they stand the rough usage of the moulding shop better and retain the sharp corners, which, if pine be used, in time become rounded impairing the appearance of the casting. Mahogany is not liable to warp, nor subject to decay; and it is exceedingly durable, and is for these reasons the most desirable of all woods employed in pattern-making, providing that first cost is not a primary consideration. There are various kinds of this beautiful wood: that known as South American mahogany is chiefly used for patterns.
Next to mahogany we may rank cherry, which is a very durable wood, but more liable to twist or warp than mahogany, and it is a little more harsh to the tool edge. If, however, it is stored in the workshop for a length of time before being used, reliable patterns may be made from it. In addition to these woods, walnut, beech, and teak are sometimes employed in pattern-making.
The one property in all timber to be specially guarded against is its tendency to warp, bend, expand, and contract, according to the amount of humidity in the atmosphere. Under ordinary conditions, we shall be right in supposing a moisture to be constantly given off from all the exposed surfaces of timber; therefore planks stored in the shop should be placed in a rack so contrived that they do not touch one another, so that the air may circulate between the planks, and dry all surfaces as nearly alike as possible. If a plank newly planed be lying on the bench on its flat side, the moisture will be given off freely from the upper surface, but will, on the under surface, be confined between the bench and the plank: the result being that a plank, planed straight, and left lying as described, will be found, even in an hour, to be curved, from the contraction of the upper surface due to its extra exposure; therefore it is obvious that lumber newly planed should be stored on end or placed on edge. Lumber expands and contracts with considerable force across the grain; hence if a piece, even of a dry plank, be rigidly held and confined at the edges, it will shrink and break in two, often with a loud report. There is no appreciable alteration lengthwise in timber from the above causes; and if two pieces be glued together so that the grain of one crosses that of the other, they can never safely be relied upon to hold. Hence they had better be screwed so that there will be a little liberty for the operation or play of the above forces, while the screws retain their hold. The shrinkage, expansion, and warping of timber may perhaps be better understood by the following considerations: The pores of wood run lengthwise, or with its grain, and hence the moisture contained in these passes off more readily endwise or from any surface on which the pores terminate.
The Shrinkage of Timber.—The direction in which timber shrinks in seasoning or drying is shown in the following figures, which are extracted from a lecture delivered by Dr. Anderson before the Society of Arts in London, England. The shrinkage of timber lengthwise of the grain is very slight, its shrinkage in a direction across or at a right angle to the length of the grain being much greater and depending upon the part of the log from which it is cut.