Modern Machine-Shop Practice Part 201

[Ill.u.s.tration: Fig. 3061.]

[Ill.u.s.tration: Fig. 3062.]

[Ill.u.s.tration: Fig. 3063.]

Fig. 3059 represents 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 base is 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. 3060 represents a female die, and Fig. 3061 plan of another female die, and Fig. 3062 plan 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.

[Ill.u.s.tration: Fig. 3064.]

[Ill.u.s.tration: Fig. 3065.]

[Ill.u.s.tration: Fig. 3066.]

Figures from 3063 to 3066 represent 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 in Figs. 3064 and 3066.

[Ill.u.s.tration: 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, in Fig. 3068 are shown a pair of rolls A B, P representing a piece of work, and C D two cam pieces fast upon the roll surfaces; S is a fixed stop.

Suppose the work to be pushed through the rolls and to rest against the stop S, then when the cams C D meet it they will pull it 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 pa.s.sages of the work through the rolls.

[Ill.u.s.tration: Fig. 3068.]

[Ill.u.s.tration: Fig. 3069.]

The shape of the cams, as C D, determines that of the work; thus in Fig.

3069 is 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 circ.u.mference of the rolls, two, three, or more cams may be arranged around the circ.u.mference, making an equal number of forgings or impressions, as the case may be, at each revolution of the rolls.

In Fig. 3067 is 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 princ.i.p.al 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 finis.h.i.+ng.

The successive operations by which each nail is perfected are as follows:--

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.

[Ill.u.s.tration: Fig. 3070.]

Figs. 3070 and 3071 represent 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 in Fig. 3070, and a vertical of it shown in Fig. 3071. In the former figure, _a_ _b_ are the screw dies.

The rod or bolt to be threaded is placed upon the lower die _b_, and fed forward while s.c.r.e.w.i.n.g it. The upper die is mounted on a slide _c_, which is actuated in the downward direction by an eccentric _e_ on the main shaft and the toggle-bar _d_, the upward motion being obtained by an internal spiral spring _f_. The lower die _b_ is carried in a slide _g_, and is adjusted at the proper distance from the upper die by means of wedge _h_, and the inclined plate _i_, beneath the slide _g_. The wedge _h_ is operated by a pedal _l_, and secured in its highest position by a bolt _j_, received in a mortice made in the plate _i_, the bolt being operated by a pedal _m_. In order to release the wedge and return it to its lowest position, the bolt is raised by pressing down the pedal _m_, whereby the wedge is free to be returned by the counterweights _k_, in connection with pedal _l_; slide _g_, 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 wedge _o_, with screw adjustment, is disposed below the inclined plate _i_.

Fig. 3072 represents a lag screw forged by the machine.

[Ill.u.s.tration: Fig. 3071.]

[Ill.u.s.tration: Fig. 3072.]

[Ill.u.s.tration: Fig. 3073.]

Fig. 3073 represents a finis.h.i.+ng machine for horseshoes. The bars 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 pa.s.s to a machine, Fig. 3073, which consists of a frame A B, carrying the roll C, above the table D, and a second roll, not shown in the cut, but being directly beneath C, there being between these two rolls sufficient s.p.a.ce to let the dies (which press the shoes into shape) pa.s.s.

These dies rest upon the table D, and are carried around upon it in a direction from left to right of the chain H, to the links of which the dies are attached. This chain is operated by the vertical shaft J, having a pulley for belt power at K.

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 roll C, which presses the shoe into the die is driven by power.

[Ill.u.s.tration: Fig. 3074.]

[Ill.u.s.tration: Fig. 3075.]

A plan view of the machine is shown in Fig. 3074, and a view showing the shape of the dies is given in Fig. 3075.

[Ill.u.s.tration: Fig. 3076.]

The surface _h_ forms the frog. To give the required concavity to the toe and sides of the shoe, the surface _i_ is made convex, and tapered or inclined towards _h_. The tread _e_ is deepest at the heel on both sides, and highest at the toe. It is obvious that by suitably shaping the surfaces _h_, _i_, and _e_, any required form may be given to the shoe. Fig. 3076 represents a shoe creased, punched, and bent ready to be pa.s.sed to the machine.

[Ill.u.s.tration: Fig. 3077.]

Fig. 3077 represents a circular saw for cutting off hot iron; A is the frame of the machine, the arm B pivoted at C carrying the saw D; F is a spring bolted to the frame and serving to hold the saw in the position shown. The work E is gripped by the lever L, which is pushed over by hand. The lever L is adjusted to suit different sizes of work by the screw G, which raises or lowers the piece H, to which L is pivoted. The saw is brought into contact with the work, and fed to it by applying the foot to the lever or arm B at I, the screw J being made to contact with the foot of the machine by the time the saw has pa.s.sed through the work, thus preventing the saw from moving too far forward after pa.s.sing through the work.

CHAPTER x.x.xIV.--WOOD-WORKING.

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, quant.i.ties 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 pa.s.ses 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.

[Ill.u.s.tration: Fig. 2706.]

The shrinkage is greater on the outside than near the heart of the tree; thus if a log be cut into four quarters it will shrink as in Fig. 2706, from the full block outside to the inside or white outline; or if we cut out a square as in figure, one corner extending to the heart, it will shrink to the form shown in the figure. If we sever the log by the four parallel saw cuts it will shrink as shown by the black outline, the shrinkage of the middle piece being more clearly shown in Fig. 2707.