Fig. 66.
Fig. 66.
This position I shall now endeavour to explain, using a diagram from an American work, in which this generally supposed difficult point is thus ably and satisfactorily explained. First, put your engine together as if for work, and having cut the eccentric rod to about the length you seem to require, judging from your plan drawn upon the bed-plate, turn round the eccentric, with your fingers upon the crank-shaft, and, having removed the cover of the valve-box, so that you can see the action on the valve, watch the motion of the latter. Doubtless, the result will be that one of the steam-ports will be opened clear to the exhaust-port, while the other is nearly or entirely shut. The rod is then too long or too short. If in a horizontal engine the port nearest to the crank is wide open and the other shut, the rod is too long, and must be shortenedhalfthe difference only (youwill do this by screwing it farther into the eccentric hoop). When the valve “runs square,” or opens and shuts the ports correctly, set the eccentric as in the diagram, H, in respect to the crank,i.e., with its widest part at right angles to it. By running square is meant that when the eccentric is turned round as described, the valve opens the ports equally, and does not affect one more than the other. The lineaof the diagram shows that the position of the eccentric may advantageously be alittlebeyondthe right angle to the crank, to give what is called “lead,”i.e., to open the valve a little before the piston commences its return-stroke.
The boilers of model engines are made of tin, sheet-brass, or copper; seldom of the latter, which is, nevertheless, by far the best material, and one that you can braze, rivet, or solder satisfactorily, or bend into any shape with a hammer or wooden mallet. When polished, too, its rich red colour is very handsome. Brass is chiefly used from the facility of obtaining tubes of it ready brazed or soldered, from which any desired length can be cut. A brazed copper boiler will stand a great deal of pressure; will tear, and not fly into pieces when it bursts; and may be heated after the water has boiled away without suffering any injury. It would certainly not be worth while to make one for a model engine with a half-inch cylinder, but for one of 1 inch diameter and 2½ stroke; and for larger sizes, it will amply repay the trouble; and I will show you how to make one, with a tube or flue inside to add to the heating surface.
I shall endeavour presently to give the proper dimensions of boilers to work cylinders of given diameters, but the general directions here subjoined apply to all boilers of models, whether large or small. The main body of the boiler is generally cylindrical, and is, in fact, a tube of sheet-metal, with riveted, brazed, or soldered seams, the last greatly predominating in the toy engines; the result ofwhich is, that the first time the water gets too low, out drops the bottom, or, at the least, divers leaky places appear, and the boiler is obliged to go to the tinman’s for repair, its beauty being ever after a thing of the past. It is difficult to braze in an ordinary fire; because even if, by blowing it with a pair of bellows, you get sufficient heat, you cannot always manage to apply your work in a good position, as you can over the hot coals of a forge fire, where there are no bars, hobs, or other parts of the grate standing in the way. Moreover, you often want both hands free just as the solder commences to “run,” and forge-bellows will keep up the blast for a few seconds after your hand is taken from the staff or handle of them. Still, if you have no forge, which is probable, you should make a fire of cinders or coke (the latter if possible); and if you can contrive a grate by putting together a few bricks in some out-house, with a bar or two of hoop-iron below for the coke to rest upon, you will have a far more convenient fire to work at than can possibly be obtained in any ordinary household grate or stove. You will require a pair of light tongs, whichoughtto be something like A, Fig. 67; but it is quite possible to do without these if you can hold your work in any other way; as, for instance, with a loop of iron wire twisted round it and left long enough to form a handle.
The first thing to do is to cut a strip of copper large enough to make the required tube. A piece 6 inches widewill roll up into a cylinder of about 2 inches diameter (the circumference of a circle being nearly equal in all cases to three times its diameter, or measure through the centre). If, therefore, you want one 6 inches across, which is the smallest size that can be advantageously fitted with a flue or internal tube, you must cut it out 18 inches wide, and if it is 8 in length to the bottom of the steam dome, it will be a large and serviceable boiler, fit to work an engine with a cylinder of 1½ bore by 2½ or 3 inch stroke, which would drive a small lathe. But observe that if you really have pluck and skill enough to try your hand upon an engine that will give you realpower, you must take care to remember that “the strength of anything is the strength of itsweakestpart.” So don’t make the very common mistake of having a good boiler and ample cylinder, and then fit the engine with piston-rod, valve-rod, and such like, too small to bear the strain which you propose to put upon the engine. Remember that every screw and nut and pin upon which strain is liable to fall, must be of sufficient size and strength to bear it safely: if not, your engine will not only come to grief in the heavy trial, but it is quite possible that you also may become subjected to a bad scald or other disagreeable consequence of your error.
Whatever sized strips of copper you use for a boiler, the edges have to come together to form what is called a butt-joint;i.e., they do not overlap like the ordinary joints yousee made in tin. Before you coil up the strip into a tubular shape, you have to cut out holes for any boiler fittings you may wish to add, such as safety-valve, steam-dome, and gauges to ascertain the level of the water. These, however, do not all come into the cylindrical part of our present boiler; the gauge-taps and glass water-gauge alone having to be provided for. The man-hole, too, which is added to all large boilers, may be dispensed with, its object being to enable one to get at the inside, which will scarcely be necessary if our work is well done at first. A boiler of the proposed size should be heated with charcoal, as it would require a very large lamp; but where gas can be obtained, it may be preferably used, a ring gas-burner being placed below within the furnace. The object of a steam-dome, which, in a horizontal boiler, would have to be placed somewhere on the tube itself, is to prevent what is called priming,i.e., the carrying into the cylinder water as well as steam, which arises from the spurting caused by the violent boiling of the water. The dome merely provides a chamber for dry steam above the general level of the boiler, the steam-pipe passing from it direct to the cylinders. Our present boiler will be vertical like the last, but with a flue up the middle, and a grate fitted below. It is shown complete in Fig. 67, B, with all the fittings usually attached.
Having coiled up the tube by hammering it over acylinder of wood turned for the purpose, a little smaller than the intended size of the boiler (the edges having been previously filed up bright, and a width of a quarter of an inch of the upper being similarly cleaned on the inside all along the seam), a few loops of iron wire are tied round it, at intervals of 1 inch or 1½ inches; there being a short piece put round, and twisted together at the ends by a pair of pliers. The object of these is to prevent the seam from opening on the application of heat, which it is otherwise certain to do by the expansion of the metal. Some borax, pounded in a mortar, and heated to drive off the water of crystallisation, is next mixed with a little water to form a creamy paste, and smeared along the inside of the tube, upon the brightened part, the full length of the seam. It is generally better to heat this salt first sufficiently to dry it (or rather fuse it), because it swells prodigiously by the first application of heat, and if the spelter is laid on it, it often carries it off; after once fusing, it only melts quietly.
Before applying the little lumps of spelter, turn over the tube to heat the part opposite to the seam, so as to equalise the expansion. Then hold it in a pair of light tongs, lay the spelter all along upon the borax, and expose it without actually touching the coals to the heat of the fire, urged by a strong blast. Continue this until a blue flame arises, which shows that the spelter has melted; this blueflame being, in fact, that caused by the burning of the zinc in the solder—spelter being copper and zinc fused together, or, if required softer, brass, tin, and zinc. The former is generally used, however, on copper. When the blue flame arises, the solder runs into the joint, and the work is done. With the hardest of these spelters, a red heat will not seriously affect the joint, and, therefore, if at any time the water should get below the line of this seam, so that it becomes exposed to the heat, no harm will be done. Nevertheless, this ought never to occur, as a gauge should be attached to every boiler to show the exact position of the water at any given time.
The inside tube of this boiler will be seen, from the section, to be conical up to the level of the lower part of the chimney. This is of copper, brazed like the cylindrical part, and is 2 inches wide below, and 1 inch above; consequently, the strips to make it must be 6 inches wide at one end, and taper to 3 inches at the other. If the dome rises 2 inches from the level of the top of the cylinder, it will be sufficient; and as this is a difficult piece of work for a boy to manage, a coppersmith should be asked to hammer the dome into the required form, as he will know from experience the best size of circular disc to use for the purpose. This part is so far removed from the action of the fire that it may safely be soldered, but it is, nevertheless, as well to rivet it, turningoutboth the edge of thecylinder and that of the dome. Use copper rivets, and make the holes half an inch apart. If you find any leakage, you can run a little solder into the joint on the inside. The bottom of the boiler may be quite flat and brazed, a few rivets being first put in to hold the parts accurately together. The same may be said of the tube which passes through both this and the dome. There is nothing equal to riveting and brazing for this kind of work.
I may as well state however here, that as such a boiler as I have now described is worth very good work, it would be a great pity to spoil it; and it will be better to content yourself with smaller boilers and engines soldered, where necessary, until you have had some practice in brazing. This indeed is not difficult in reality, but, at the same time, requires great care, because sometimes the solder and the work melt at so nearly the same temperature, that, like a bad tinker, you will sometimes make two holes instead of mending one. The brass, for instance, used for beer-taps is very soft, and contains lead, and to a certainty would itself melt before ordinary spelter, and could not therefore be brazed; but the best Bristol brass, or yellow metal, will braze easily. A blacksmith, brazing a key or other iron article, will braze it in a different way, using brass wire, with which he will envelop the parts thickly which are to be united, after securing their position withironbinding-wire. He then sprinkles with borax, and heats the work until the wire runs into the joint; after which he files and cleans off level. This makes a very good medium.
Fig. 67.
Fig. 67.
I have spoken ofrivetingin this place. There is no difficulty in this work. You can buy copper rivets of all sizes, and have only to punch holes, put a rivet in place, and hammer it so as to spread the metal to form a second head. If the rivets are heated before being applied, they will draw the parts closer together, because they shrink in cooling. All large boilers are made in this way, but smaller ones of iron are oftenwelded, where such a mode of junction is possible. When you can rivet boilers water and steam tight, you will find no difficulty in constructing them, for you can make riveted joints where brazing would be difficult or impossible.
Fig. 68.
Fig. 68.
Fig. 67, B, is a half-section of such a boiler as I have just described. Fig. 68, A, is the lower part, which is separate, and forms the furnace in which the boiler stands, fitting it closely. This is drawn to scale, and is half the real size.ais the steam-pipe, fitted high up in the dome, the tap,b, serving to turn on or off the supply of steam for the cylinder;cis the safety-valve shown in section, and care must be always taken to make the conical part short and of a large angle, or it may stick fast, and cause an explosion;dis the glass gauge, to show the exact height of the water in the boiler. Its construction will be understoodfrom the other which is attached, where the boiler is seen in section. There is no need to have two, and this is added solely to explain the nature of glass-gauges. The top and bottom are of brass, being tubes screwing into the boiler, or fastened by a nut inside; a tube,g, of thick glass, connects these two, so as to form a continuous tube, one end of which opens into that part of the boiler which is full of steam, the other opening below the water-level. Thus the tube forms practically part of the boiler, and the level of the water is clearly seen. The lower tap is used for blowing off water, to insure the communication being kept open, as it might get stopped up with sediment.
Gauge-cocks,e,f, are generally added, even where the glass water-gauge is used. One of these should always give steam, the other water,—the level of the latter being between the two. If the upper one gives water, the boiler is too full; if both give steam, the boiler needs to have water added. With these fittings, even a soldered boiler ought never to get burnt, and will last a long time with care.
The lower part, Fig. 67, is made like that before described, except that, being intended for charcoal, a circular grate is used, which simply rests upon little brackets fixed by rivets for this purpose. The flame and heat play upon the bottom of the boiler, and also pass up the central tube—the latter adding greatly to the quantity of steam produced.This furnace, when lighted, may be fed with bits of coke as well as charcoal, about the size of filberts, and will give plenty of heat. If the draught, however, is deficient, turn the waste steam into the tube, so as to form a jet at each stroke, and it will greatly increase it. It is in this way that the locomotive engines are always fitted, George Stephenson having first suggested the arrangement. Previously to this a fan had been fitted below the grate, which was put in rapid motion by the engine, and thus a sufficient draught was obtained.
To find out what pressure is exerted by the safety-valve, it must be clearly understood upon what principle it acts. I have in a previous chapter told you that the atmospheric pressure equals 15 lbs. on each square inch, so that if the surface of the valve which is exposed to the air is 1 inch in area or surface, it is pressed down with a force of 15 lbs. The steam, therefore, inside the boiler will not raise it until its elasticity exceeds this atmospheric pressure. If, therefore, we desire to have only just 15 lbs. per square inch pressing against the inside of the boiler (i.e., a pressure of “one atmosphere,” as it is called), we have only to load the valve so that, inclusive of its own weight, it shall equal 15 lbs. But it is plain that we must not load it at all in reality; for a flat plate, 1 inch square, ofno weight,is all that is needed, the atmosphere itself being the load. Suppose, then, that wedoload it with 15 lbs. in addition to the 15 lbs. with which nature has loaded it, we shall not find the steam escape until it presses with a force of 30 lbs. on the square inch, or two atmospheres (which, however, is not 30 lbs. ofusefulpressure upon one side of the piston, if the cylinder is open as in an atmospheric engine, but only 15 lbs.) This is not thestrainwhich the boiler has to stand, because the atmosphere is pressing upon it and counteracting it up to the 15 lbs., so that this strain tending to burst it is but 15 lbs. The number of pounds, therefore, which is straining the boiler can readily be seen; being always that with which the safety-valve is loaded, and this is also the useful pressure for doing any required work. Unfortunately, however, even in the best constructed engines, a pressure of 15 lbs. upon the boiler by no means represents that in the cylinder. Now it would be inconvenient to place weights upon the safety-valve itself, and therefore a lever is added, as seen in the sketch, with a weight hung at one end of it. This is shown at B, Fig. 68, where a section of the valve is given with its stem passing through a guide to insure the correct motion of the valve. The lever is hinged at one end; and the rule of the pressure or weight which is brought to bear upon the valve is, that it is multiplied by the distance at which the weight hangs from the valve, compared with its distance from the hingeor fulcrum. If a weight of 7 lbs. is hung at 1,i.e., at a distance as far on that side of the valve as the fulcrum is on the other side of it, 7 lbs. will be the actual power exerted; at 2, where it is twice the distance, it will be doubled, and, as shown in the drawing, a pressure of 14 lbs. will be brought to bear upon the valve; while, if the weight is hung at 3, it will exercise a force of 21 lbs. This is very easy to understand and to remember. Sometimes (always in locomotives) the weight is removed and a spring balance is attached at the long end. Upon this is marked the actual pressure exerted; there being a nut to screw down, and thus bring any desired strain upon the spring. Mind, however, in case you should try this in any of your models, that the scale marked on the balance when you buy it must be multiplied, as before, according to the length of your lever. Thus, if I attach such a balance at 3 of the drawing, a real weight of 5 lbs. shown by the balance will be 3 × 5, or 15 lbs. upon the valve, and a balancemade for such enginewould be marked 15 lbs., to prevent the possibility of dangerous error.
Having been led on from the atmospheric engine to that of Watt’s, and to slide-valve engines generally, I am now going backward a little to a class easier to make, because they have no slide-valves, nor even four-way cocks; andthen I shall have done with engines. But I dare say some of my readers will wonder why I have said so little about condensers and condensing engines. I am sure they will wonder at it if they understood what I explained of the advantage of a vacuum under the piston; so that 15 lbs. pressure upon the piston means 15 lbs. ofusefulwork, instead of 30 lbs. being required for that purpose. But condensing engines are utterly beyond a boy’s power. They require not only a vessel into which the steam is injected at each stroke, but there must be a pump to raise and inject cold water to condense the steam, and a pump to extract from the vessel again this water, after it has been used, and a cistern, and cold and hot wells; and all this is difficult to makeso as to act; and I am sure no boy cares for a steam engine that will not work. Moreover, I have given you difficult work as it is—work that many of my readers will no doubt be afraid to try—yet I did it on purpose; because if small boys are unequal to some of it, their big brothers are not, or ought not to be; and mechanical boys must look at difficulties as a trained hunter looks at a hedge—viz., with a strong desire to go over it, or through it, or any how and some how to get to the other side of it. Indeed, you must ride your mechanical hobby very boldly and with great pluck, or you won’t half enjoy the ride. However, I am quite aware that I have led you into several difficulties, and therefore now I propose to set before yousome easy work as a kind of holiday task which will send you with fresh vigour to what isnotso easy.
The engines without slide-valves have also no eccentrics and no connecting-rods. There is just a boiler, a cylinder, piston, piston-rod, and crank, and you have the sum total, save and except the fly-wheel. These are direct-action engines, the cylinders of which oscillate like a pendulum, and the piston-rod itself is connected to the crank, doing away with the necessity for guides.
Fig. 69, A, shows one of these engines, and you see that the cylinder leans to the left when the crank is turned to that side; and if you turn the wheel to the right, the crank will presently cause it to lean the other way; and thus, as it turns on a pin, or “trunnion,” as it is called, it keeps on swinging from side to side as the wheel goes round.
Now, when it is in its first position, the piston is at the bottom of the cylinder, and it then needs to have the steam admitted below it to drive up the piston; but when this has passed its highest position, and the cylinder is turned a little to theright, the piston must be allowed to descend, and, therefore, we must let out the steam below it. Weought, at the same time, to admit steam above the piston to force it down; but, in the simplest models, which are called single-action engines, this is not done. The fly-wheel, having been set in motion, keeps on revolving, and, by its impetus, sends down the piston quite powerfullyenough to overcome the slight resistance which is offered by the friction of the parts.
Now, you can, I daresay, easily understand that it is possible to make this to-and-fro motion of the oscillating cylinder open first a steam-port to allow steam to raise the piston, and then an exhaust-port to let it blow off into the air. This is exactly what is done in practice, and it is managed in the following manner:—
Fig. 69.
Fig. 69.
B, of Fig. 69, shows the bottom of the cylinder, which is a solid piece of brass filed quite flat on one side, and turned out to receive the end of the brass tube, which, generally speaking, is screwed into it to form the cylinder, this being the easiest way to make it. In the middle of the upper part of the flat side you see a white steam-port, and below it a round white spot, which is the position of the pin, ortrunnion, on which it oscillates. Fig. 69, C, is a similar piece of brass, which is fixed to the top of the boiler. In this, on theleftof the upper part, is also a port, which is connected with the boiler by a hole drilled below it to admit steam. On the right is also a port, which is merely cut like a notch, or it may go a little way into the boss, and then be met by a hole drilled to meet it, so as to form the escape or exhaust port. Between and below these is the hole for the trunnion.
Now, you can, I think, see that if the cylinder stands upright against this block, as it does when the crank is vertical (or upright) and on its dead points, the port at the bottom of the cylinder would fall between the two on this block of brass, and, as they are both flat and fit closely, no steam from the boiler can enter the cylinder. Nor do we want it to do so, because, if the crank is on a dead point, no amount of steam can make the piston rise so as to move it. But now, if we move the cylinder to the left, which we can do by turning the wheel, we shall presently get the crank at right angles to its former position, and, also, we shall bring the steam-ports in the cylinder and block together, so that steam will enter below the piston. But, practically to get as long a stroke as possible, steam is not allowed to enter fully until the crank is further on than in a horizontal position, that is,approachingits lower dead point; and this is the position in which to put it to startthe engine. By altering the shape or the position of the port a little, we can so arrange matters as to let steam enter at any required moment.
Steam having entered, the piston will rise rapidly, forcing up the piston, and presently, by the consequent revolution of the fly-wheel, the cylinder will be found leaning to the left, and at this moment the piston must evidently begin to descend. At this very time the steam-ports will have ceased to correspond, but the port in thecylinderwill come opposite the exhaust-port in the brass block, and this port is made of such size and shape that the two shall continue to be together all the time the piston is descending; but, the moment it has reached the end of its downward stroke, they cease to correspond in position, and the steam-port begins again to admit a fresh supply of steam.
The pillar attached to the brass boss has nothing to do with it, but is one of the supports of the axle of the fly-wheel, as you will understand by inspection of A of this same drawing.
Such is the single-action model engine,of no power, but a very interesting toy and realsteamengine.
The double-action engine is very superior to the foregoing, which, I may remark, has no stuffing-box, and of which the piston is never packed. I may also add, that the crank is formed generally by merely bending the wire that forms the axle of the wheel, and putting the bent end through the holeof a little boss or knob of brass, screwed to the end of the piston-rod. Here you have no boring of cylinders to accomplish, but the cylinder cover, piston, and wheel (often of lead or tin) require the lathe to make them neatly. Many an engine, however, has been made without a lathe, and I have seen one with a bit of gun-barrel for a cylinder, and a four-way cock of very rough construction, that was used to turn a coffee-mill, and did its work very well too.
But I must go at once to the double-action oscillating cylinder, in which, although a similar mode of admitting steam is used, it is arranged to admit it alternately above and below the piston, the exhaust also acting in a similar manner.
After the explanation I have given you, however, of the single-action engine, you will, some of you, I think, jump at a conclusion almost directly, and perhaps be able to plan for yourselves a very easy arrangement to accomplish the desired end. All boys, however, are not “wax to receive, and adamant to retain” an impression; for I have known some who need an idea to be driven into their brains with a good deal of hard hammering. Stupid?—No. Dull?—No, only slow ingetting hold, and none the worse for that generally, if the master will but have a little patience; for when theydoget hold, they are very like bulldogs, they won’t let go in a hurry, but store up in most retentive minds what they learned with such deliberation.
The cylinder of the double-action engine is of necessity made with ports very similar to those of the horizontal engine already described. There is a solid piece attached to the cylinder as before, which is drilled down to the upper and lower part respectively of a central boss, turned very flat upon the face, and which has to work against a similar flat surface as in the last engine. But the ports in the latter are four instead of two, and in an engine with upright cylinder would be cut as follows, and as shown in Fig. 70, C.
Fig. 70.
Fig. 70.
Those on the right markedstare steam-ports, which, being drilled into one behind, are connected with the boiler. The other two markedex, are similarly exhaust-ports opening into the air. The spaces betweena bandc dof fig. C must be wide enough to close the steam-ports in the cylinder, when the latter is perpendicular and the engine at rest. When the cylinder leans to the left, oscillating on the central pin between the ports in the middle of the circle, the lower port of it will evidently be in connection with the steam-port in C, while the upper port of the cylinder will be opposite to the exhaust. As the cylinder is carried over towards the right, the upper steam-ports will come into action in a similar way, while the lower exhaust-port is also carrying off in turn the waste steam. The impetus, therefore, of thefly-wheel has here only to carry the ports over the spacesa b,c d, and to prevent the crank stopping on the two dead points. This, therefore, is a genuine double-action engine, and will answer, even on a large scale, very satisfactorily. If you do not quite understand the action of these ports, cut out two pieces of card, E F. Let E represent the cylinder. Draw circles, and cut two ports. Cut another piece of cardto represent the brass block, with ports,c d; pin them together through the centres of the circles, and they will easily turn on the pin. Mark the ports, so that you will see at a glance which are steam and which exhaust. Now cut out the ports with a penknife, and as you work the two cards together, swaying that which represents the cylinder to and fro upon the other, you will see when the ports in each card agree with one another, and which are opposite to which. This will teach you far better than any further written explanation. You will also see that, instead of making the steam and exhaust ports respectively with a division between, the two steam-ports may be in one curve united, and likewise the two exhausts; but take care not to unite the exhaust with the steam-ports. There is no way so easy as this of reversing the action of the steam; it is, in fact, a circular slide-valve, but wonderfully easy to make, because you have no steam-case to make, nor any attachments whatever.
The faces of the valve are kept in close contact in one of two ways—either the centre-pin is fixed into the cylinder face, and after passing through the brass boss with the ports, is screwed up with a nut at the back; or else there is fixed a small pillar or upright on the opposite side of the cylinder, and a little pointed screw passing through this presses against the cylinder, and makes a point of resistance, against which it centres, and on which it turns. Thisis shown at fig. A. A small indentation is made where the point comes in contact with the cylinder.
In a locomotive engine there are two such cylinders, working against opposite faces of the same brass block containing the ports. The cranks are also two, on the shaft of the driving-wheels, and are at right angles to each other; so that when one piston is at the middle of its stroke, the other is nearly or quite at the end of it. Thus, between the two there is always some force being exerted by the steam; and the dead points of one crank agree with the greatest leverage of the other. In locomotives, too, the cylinders generally are made as in the present drawing, viz., to oscillate on a point at the middle of their length; but it is just as easy to have the two ports meet at the bottom instead, so that the point of oscillation may be low down, like the single-acting cylinders of the last sketch, and this is generally done when the cylinder is to stand upright.
There is no occasion for me to draw an engine with double-acting oscillating cylinders, because in appearance it would be like the single-acting one; but whereas the latter is of absolutely no use, seeing that the greater part of its motion depends on the impetus of the fly-wheel, the former can be made to do real work, and is the form to be used for marine and locomotive engines. For the former, oscillating cylinders with slide-valves are used in practice;but for real locomotives fixed cylinders are always used. Of course either will answer in models, and it will be good practice to try both.
I have now given sufficient explanation of how engines work, and how they may be made, to enable my young mechanic to try his hand at such work. The double-action oscillating engines especially are well worthy of his attention, as he may with these fit up working models of steam-boats and railway trains, which are far more difficult to construct with fixed cylinders and slide-valves. I shall therefore close this part of my work with a description of one or two useful appliances to help him in the manipulative portion of his labour,—for here, as in most other matters, head and hand and heart must work together. The heart desires, the head plans, the hands execute. I think, indeed, I might without irreverence bring forward a quotation, written a very long time ago by a very clever and scientific man, in a very Holy Book: “Whatsoever thy hand findeth to do, do it with all thy might.” Depend upon it, success in life depends mainly upon carrying into practice this excellent advice. If you take up one piece of work, and carelessly and listlessly play at doing it, and then lay it down to begin with equal indifference something else, you will never become either a good mechanic or a useful man. If you read of those who have beengreatmen—lights in their generation—you will find generally thatthey became such simply by their observance of that ancient precept of the wise man. They were not so marvellously clever—they seldom had any unusual worldly advantages; but they worked “with all their might,” and success crowned their efforts, as it will crown yours if you do the same.
I promised in a previous page to describe a little stove for heating soldering-irons, and doing other light work. It is made as follows, and will be found very useful.
Fig. 71, A, is a tube of sheet-iron, which forms the body of the little stove. Four light iron rods stand out from it, which form handles, but these are forked at the ends, and thus become rests for the handles of soldering-irons, or any light bars that are to be heated at the ends. Below is a tray, also of sheet-iron, upon short legs to keep it off the table—for this is a little table-stove. C is the cast-iron grate. You can buy this for a few pence first of all, and then you fit your sheet-metal to it. It will rest on three or four little studs or projections riveted to the stove inside; or you can cut three or four little places like D, not cutting them at the bottom line,a b, but only on three sides, and then bend in the little piece so as to make ashelf. If the stove is about 4 inches high above the grate, and 2 or 3 inches below it, and 6 inches diameter, it will be sufficiently large for many small operations; but that the fuel may keep falling downwards as it burns, the lower part should be larger than the upper, and, to admit plenty of air, should be cut into legs as shown. Round the top are cut semicircular hollows, in which the irons rest. To increase the heat, a chimney or blower, B, is fitted, which has also openings cut out to match those of the lower part, so that the soldering-irons can be inserted when this chimney is put on. If, however, this is not required, but only a strong draught, by turning the chimney a little, all the openings will be closed. A still longer chimney can be added at pleasure. A hole should be made at the level of the grate to admit the nozzle of an ordinary pair of bellows. This stove you would find of great service, and it may be fed with coke and charcoal in small lumps. Now youmaymake the above far more useful. It will make a regular little furnace, and not burn through, if you can line it with fireclay. In London and large towns you can obtain this; and it only needs to be mixed up with water, like mortar, when you can plaster your stove inside an inch thick or more, making it so much larger on purpose. There is no need to do this below the level of the grate; but if you cannot get fireclay, you may do almost as well by getting a blacklead-meltingpot from any ironfoundry,and boring a few holes round the bottom for air, and fitting it inside your little iron stove. In this you can obtain heat enough to melt brass, and it will last a great deal longer than the iron alone, which will burn through if you blow the fire much; but for general soldering, tempering small tools, and so forth, you need not blow the fire, as the hood and chimney will sufficiently increase the heat. There is no danger in the use of this little fireplace, but of course you would not stand it near a heap of shavings, unless you are yourself a very careless young “shaver.”
Fig. 71.
Fig. 71.
There is no reason why the young mechanic should notbe told how to make his own tools, and how to harden and temper them, because he ought to be a sort of jack-of-all-trades; and perhaps he may break a drill or other small tool just in the middle of some special bit of work, or his drill may be just a little too small or too large, and there he will be stuck fast as a pig in a gate, and unable to set himself right again any more than the noisy squeaker aforesaid. But to a workman a broken drill means just five minutes’ delay, and all goes on again as merrily as before; and as we wish to make our young readers workmen and not bunglers, we will teach them this useful art at once.
Drills are made of steel wire or rods of various sizes. In old times they were made square at one end, to fit lathe-chucks or braces, but now, for lathe-work, they are generally made of round steel, and fastened into the chuck with a set screw on one side. In this way they can be more easily made to run true. But there are so many kinds of drills that I suppose I had better go into the matter a little—only I have not room to say much more.
Fig. 72.
Fig. 72.
Look at Fig. 72, and you will see some of the more usual forms of drills used, but these are by no means all. You will not indeed require such a collection; and yet, if you should grow from a young mechanic into an old one, I daresay you will find yourself in possession of several of them. The first, labelled 1, is the little watchmaker’s drill, ofwhich, nevertheless, this would be considered a very large size. It is merely a bit of steel wire, with a brass pulley upon it, formed into a point at the largest end, and into a drill at the other. The way it is worked is this: At the side of the table-vice—that is, at the end of its jaws or chops or chaps—are drilled a few little shallow holes, in which the watchmaker places the point at the thickest end; the drill-point rests against the work, which he holds in his left hand. A bow of whalebone,a, has a string of fine gut such as is used for fishing, or, if the drill is very small, a horse-hair; and this is given one turn round thebrass pulley before the drill is placed in position. The bow is then moved to and fro, causing the drill to revolve first in one direction and then in the other. The general work is in thin brass, and therefore these little tools are sufficiently strong for the purpose. Some of the drills and broaches (four or five, or even six sided wires of steel) are so fine that they will bend about like a hair, and yet are so beautifully made and tempered as to cut steel.
No. 2 is a larger drill, even now much used. In principle it is exactly similar to the last, but the pulley is replaced by a bobbin or reel of wood, made to revolve by a steel bow with a gut string, or a strong wooden bow. The drills, too, are separate, and fit into a socket at the bottom of the drill-stock. The large end is pointed, as in the last, and is made to rest in one of the holes in a steel breast-plate,b, which is tied to the chest of the operator, who, by leaning against it, keeps the drill to its work, while both hands are free to hold the latter steady. There is a modification of this tool, invented by a Mr Freeman, intended to do away with the bow. The bobbin or reel is turned without raised ends, and is worked by a flat strip of wood covered with india-rubber, and turned at one end to form a convenient handle. The having to twist the bow-string round the drill, which is always a bother, is thus done away with.
No. 4 is a drill-stock similar to the last, but in place ofthe breast-plate a revolving head or handle is put to the top, in which the point works. This is held in one hand, while the drill-bow is worked by the other. This is also generally held against the chest, as the hand alone does not give sufficient pressure. Heavy work, however, cannot well be done by these breast-drills, and they are liable to cause spitting of blood from the constant pressure in the region of the heart and lungs.
No. 3 is the Archimedean drill-stock, now very common, but originally invented by a workman of Messrs Holtzappffel’s, the eminent lathemakers of London. It now comes to us as an American drill-stock. It is a long screw of two or more threads, with a ferule or nut working upon it. The upper end revolves within the head, which is of wood; the lower end is formed into a socket to receive the drills, which revolve by sliding the ferule up and down. Some are 14 inches long, and others not more than 5. The first are used with the pressure of the chest, the latter with that of the left hand. For light work these are very useful, and you will seldom need any other in the models of small engines, &c.
No. 5 is another watchmaker’s drill, but serves also as a pin-vice to hold small pieces of wire while being turned or filed in the little lathes which are used in that trade, and which are worked by a bow with one hand, while the tool is held in the other. This is by no means a useless tool,even without the pulley. It is made by taking a round (or better, an octagon, or five or six sided) piece of steel, drilling the end a little distance, and then sawing the whole up the middle. The slit thus made is then filed away to widen it, and leave two jaws at the end, which grasp the pin or drill; a ring slips over, and keeps the jaws together.
We now come to fig. 6, which represents the best of all drills for metal. It isreallyAmerican this time, and does our Transatlantic cousins great credit, as does the machinery generally invented or made by them (the Wheeler and Wilson sewing-machines for instance). The steel of which this drill is made is accurately turned in a lathe, and the spiral groove is cut by machinery. This groove acts in two ways—first, as allowing theshavings(not powdery chips) to escape as the tool penetrates, but as forming the cutting edges where they (for there are two) meet at the point. These, however, require a lathe with a self-centring chuck made on purpose. They are sold in sets upon a stand, chuck and all complete, and each is one-thirty-second of an inch larger than the other. Some are as small as a darning-needle, or less, and they run up to an inch or so in diameter. There are large and small sets.
We now pass to the old-fashioned smith’s brace, fig. 7, shown in position, drilling the piecee. Pressure is kept up either by a weighted lever, or by a screw, as shownhere. The brace is moved round by the hand of the workman. Very often this tool is arranged on the vice-bench, so that the work can be retained in the jaws of the vice while being drilled. Sometimes it is mounted on a separate stand, having a stool below, and a special kind of vice or clamp is added. Well made, this is not so bad a tool as it looks, but those used ordinarily in smiths’ shops are very clumsy, and do not even run true, and the drills are badly made, although by sheer force they are driven through the work.
Whatever form of drill-stock is used, the main thing is to have the drills properly formed. You will recognisekandnas common forms, than whichmis considerably better. For cast-ironnwould not be a bad point, because the angle is great, much greater, you see, thank; and the bevels which form the cutting edges of a drill should also not be too sharp, as they are generally made, for, as they only scrape away the metal, their edges go directly.
The common way to make a drill is this: A piece of steel wire of the required size is heated until red hot (never to awhiteheat, or it would be spoiled). The end is then flattened out with a hammer, and the point trimmed with a file. It is then again heated red hot, and dipped into cold water for a second. Then held where the changes of colour, which ensue as it cools, can be seen plainly; and as soon as a deep yellow or first tinge of purple becomesvisible, it is entirely cooled in water. It is then finished, except as regards fitting it to the drill-stock, which may be done before or after it is hardened, because care is taken only to dip the extreme point. To get proper cutting edges the drill is taken to the grindstone, and each side of the point is slightly bevelled, but in opposite directions, so as to make it cut both ways. It is not, however, left of equal width, likeo, but the flattened sides are ground away, so as to make more of a point, likepandn.
Now, this is all right enough as regards forging and hardening, and tempering, and for thesmallestdrills this is the only way to make them. (Only watchmakers heat them in the candle till red, and then cool and temper by running them into the tallow.) But if you want a good drill that will cut well and truly, you should file away the sides of a round bar likem, only spreading the point very slightly indeed, just to prevent the drill sticking fast in the work. Another drill, indeed, is spoken of very highly, which is also carefully made likem, but the places which are here flat are hollowed out or grooved lengthwise, the section of the point—i.e., the appearance of theendof the drill—becomes rather curious, liker. I am assured by those who have used them, that these cut quite as well as the twist drills which I have described already. These which I am now speaking of are also American; and I don’t know how it is, that somehow America is a far better place forimprovements in tools and machines than our own Old England. And if I had a wonderful invention—a new birch-rod-making and flogging-machine for very troublesome boys, for instance—I am afraid I should go to America to patent it; but I daresay English boys would not object to that.