As previously remarked the vehicle is divided into two parts—the carriage and the body. After the drawing or draught is carefully worked out to full-size on the black-board in the shop, with all the curves and sweeps developed, and shown in elevation and plan, patterns or templates are made from the draught, and from these the construction of the body proceeds.
In commencing the construction of a vehicle there are several things to be borne in mind; such as the purpose to which the vehicle is to be applied, the size of horses to draw it, and other considerations arising from these two. It is popularly believed that the shorter the carriage the lighter it will run; in ascending an incline this may be true, but on ordinary level ground a long carriage and short one must be alike in friction, provided the total amount of weight and other circumstances be equally balanced.
Another consideration is the height of the wheels. On level ground, draught is easiest when the centre of the wheel is a little lower than the point of draught, viz. the point where the traces are affixed to the collar; but this in practice would be found rather inconvenient, as very high wheels would be required, and consequently the height of the whole vehicle would have to be increased, causing great trouble and annoyance in getting in and out of the vehicle, and the driver’s seat would have to be raised to a corresponding height. Under equal circumstances a high wheel is more efficient than a low one, and requires less power to draw it; though it may be mentioned that a low wheel on a good and level road will do its work far better than a very much higher wheel on a rougher road. The sizes of the wheels of two-wheeled vehicles vary from 3 feet to 4 feet 6 inches.
It would be a very good thing if four-wheeled vehicles were to have the wheels of equal size, in order that the friction and power might be equal. But with the present mode of construction this is an impossibility, as we have only one mode of making the lock or turn. Therefore the height of the fore wheels must be regulated by the height at which the body hangs, so that the wheels may pass beneath it without striking, when the springs play. In practice this height varies from 2 feet to 3 feet 8 inches, according to the kind of carriage the wheels are intended for. The hind wheels vary from 3 feet to 4 feet 8 inches.
The next point is the dishing of the wheel, which is necessary for strength to take the strain off the nuts, to throw off the mud and prevent it clogging either the wheel or the body, and to give greater room for the body between the wheels without increasing the track on the ground. Whatever be the amount of dishing or coning, which varies from 1½ to 2½ inches, one rule should always be observed, viz. so to form the wheel that when running the lower spokes should maintain a true vertical position both in the fore and hind wheels. This is mainly accomplished by the dip of the axle, but if the fore and hind wheels have the same dish, they will take the same track along the ground. The dish of a wheel will be understood by referring to Fig. 10, in which it will be seen that the extremities of the spokes are not in the same plane, thus forming a dish or hollow in the surface of the wheel.
Some ingenious persons have deduced from the foregoing that a wheel runs best on an axle having a conical arm (the arm is the extremity of the axle which fits into an axle-box in the nave or stock of the wheel), in which case the axle would not dip, but the wheel would be put on to a perfectly horizontal axle. The motion of a wheel thus placed would be anything but artistic, though there would not be so much friction on an arm of this sort as on an arm of the dipped axle. Dipping the axle is shown at Fig. 10. It merely consists in bending it so far out of the horizontal as to give the lower spokes a vertical position. But in practice this theory of the conical arm will not answer, inasmuch as curving the arm will reduce the front bearing surface so much that the oil would be squeezed out, and it would run dry, and the total amount of friction would be greatly increased. Long practice has shown that a cylindrical or slightly conical arm is the best that can be used.
We have now to settle the form, combination, and proportion of the springs. Springs which are laid on the axle at right angles have to carry the whole of the weight of the carriage, save only the wheels and axles. Where other springs are used in addition it is not necessary that the axle-springs should have much play. It will be sufficient to give them just so much play as will intercept the concussion caused by moving over a road. The strength of the springs must of course be adjusted to the weight they have to carry, for it is evident that if they be made sufficiently elastic to carry the weight of six persons, they will be found hard if only three enter the carriage. This is a disadvantage all carriages must labour under, for it is ridiculous to suppose that if a carriage is constructed to hold six that number will always want to use it at the same time. There would seem to be room for some improvement in the way of introducing springs adjustable to any weight, though, to give spring-makers their due, they do turn out really a first-class article in this respect; this is more noticeable because it is so recent. Light carriages are never so easy to ride as heavy ones, even when the springs are well adjusted, because on meeting with an obstacle there is not a sufficient resistance to the bound or jerk upwards of the spring, which makes riding in a light carriage over a rough road rather unpleasant.
The position of the front wheels next demands attention. As these have to turn under the body it requires some skill to fix them, and the play of the springs, the height of the axletree, and the height of the arch (the portion of the body under which they turn) have all to be considered. This will be more particularly described when dealing with wheel-plates.
The rule for the height of the splinter-bar, to which the traces or shafts are fixed, is that it should fall on a line drawn from the horse’s shoulder to the centre of the hind wheel. This, however, is not always convenient in practice, as the fore wheels regulate the height of the framing of the under carriage, to which the splinter-bar is fixed. The distance of the splinter-bar from the central pin, on which the wheel-plate and fore carriage turn, is regulated by the size of the wheels and the projection of the driving seat footboard.
All the above particulars are considered when setting out the full-sized draught, and all points capable of delineation are put on the board in some convenient part. In Fig. 9 the outline is simply given, as to show everything would only confuse the reader. Such other details as are required are filled in after the draught has reached the stage shown in the figure.
It is most necessary for the safe conduct of a coach and carriage builder’s business that there should be a goodly stack of well-seasoned timber of the various kinds required, otherwise great trouble and vexation will arise in the course of business from a good piece of timber being perhaps spoilt in working, and there not being another piece in the factory to replace it.
Where there is sufficient accommodation it is usual for makers to season their own timber in specially constructed sheds, which are kept from bad weather, but at the same time thoroughly well ventilated. In these the timber is stacked, with small fillets between each plank or board, to insure a free current of air circulating all round. One year should be allowed for seasoning for every inch of thickness in the timber, and none should be used in which this rule has not been observed.
Thin portions of timber, such as panel stuff and the like, should be treated in the same way, and in addition the ends should be secured to prevent splitting. The panel stuff undergoes another process of seasoning after it is planed up; in fact, all the thin timber required for roofs, sides, &c., does. And about the first thing done in commencing to build a carriage is for the body-maker to get his thin stuff ready, as far as planing it up goes, and then to put it aside in some moderately dry place, with slips of wood between each board to allow a circulation of air round them. The other stuff that is likely to be required should also be selected and put aside. If all these things be strictly attended to, there is not likely to be much trouble about bad joints; and it will be to the employer’s interest to look after such workmen who have not enough scientific knowledge to see the reason of things themselves, and put them in the right direction. But an intelligent workman will soon appreciate the advantage of getting his stuff ready at the commencement, instead of waiting till he wants to use it.
The parts composing the body may be thus enumerated:—
The frame or case.
The doors.
The glasses, which are fixed in thin frames of wainscot, covered with cloth or velvet. It is a very good thing to have india-rubber for these to fall on, and little india-rubber buffers would prevent them from rattling.
The blinds, which are sometimes panel, but more generally Venetian, so adjusted with springs that the bars may stand open at any required angle.
The curtains, of silk, which slide up and down on spring rollers.
The lining and cushions, of cloth, silk, or morocco, as the case may be, ornamented with lace, &c. The cushions are sometimes made elastic with small spiral springs.
The steps, which are made to fold up and fit into recesses in the doors, or in the bottom, when they are not in use.
The lamps, which are fixed to the fore part of the body by means of iron stays.
The boot, on which is carried the coachman’s seat.
In carriages suspended from C springs we have in addition:—
The check-brace rings, to which are attached leather braces from the spring heads, to prevent the body from swinging too much backwards and forwards.
The collar-brace rings, to which are attached leather braces from the perch, to prevent the body swinging too much upwards or sideways.
The curve or rounding given to the side of the body from end to end is called the side-cant, and the rounding from the top to the bottom the turn-under. Some makers arrive at this curve by framing the skeleton of the body together with square timber, and then round these off to the required curve after they are put together. It must be evident to any one that this proceeding will greatly strain the joints, and under any circumstances will never give thorough satisfaction or good results, and the waste of time and material must be very considerable.
The proper way is to set the curve out beforehand on a board called the “cant” board, and the method of doing this is as follows:—
Take a clean pine board, plane it up to a smooth surface. Shoot one edge perfectly true with a trying-plane. This straight edge may be taken to represent the side of the carriage if it were a straight line. Apply this edge to the full-sized draught, and mark along it the various parts of the body (see Fig. 8, in which the numbered points are those required to form the side-cant). By means of these points the required sweep can be set up or drawn, as shown by the dotted line C in the figure. Now, if you choose, you can cut away the portion between A and B, and a template will be formed to which the constructional timbers can be cut; and it possesses the advantage of being easily applied to the carriage as it proceeds, to see that the curve is true and uniform. As this template forms the pattern to which the timber, &c., is cut, great care is requisite in forming it, so that it shall be perfectly true.
In order to get the turn-under, the same process is gone through on another board. This gives what is called the “standing” pillar pattern, the standing pillar being the upright timber to which the door is hinged.
There is no rule in particular for determining the amount of side-cant or turn-under to be given to a vehicle, 2½ or 3 inches on each side making the outside width of the body; 5 or 6 inches less at the bottom than at the elbow line is a usual allowance, but this is entirely dependent on the will or taste of the workman.
The cant-board described above is one having a “concave” surface; but it quite as often has a convex surface, and it is just as well to have one of each, and use the convex for cutting the timbers to, and the concave for trying them when in place, though, if this be done, it is imperative that the curves on the two boards should be one and the same. The same remarks apply to the standing pillar pattern.
The body is a species of box, fitted with doors and windows, and lined and wadded for the purpose of comfort. As the greatest amount of strain is put upon the bottom part, and the forces acting on the other parts are transmitted to the bottom, it is necessary that it should be very strongly put together. The two side bottom timbers are bonded, or tied together, by two cross timbers called bottom bars, which are firmly framed into them. To give depth to the floor, without destroying the symmetry of the side, deep pieces of elm plank are fixed to the inside of the side bottom pieces, and to these the flooring-boards are nailed, being additionally secured by iron strap plates, nailed or screwed beneath them. In the central portion of the bottom sides are framed the door-posts, called standing pillars. At the angles of the bottom framework are scarfed the corner pillars. The cross framing pieces, which connect the pillars, are called rails. Two of these rails stretch across the body inside, on which the seats are formed; these are called seat rails. The doors are framed double, to contain a hollow space for the glasses and blinds, and they are fastened by means of a wedge lock, forced into a groove by a lever handle. There is a window in each door and one in front of an ordinary carriage, say a brougham. The doors are hinged with secret or flush hinges.
Before cutting the timber to the various sizes required, patterns or templates of all the parts are made in thin wood from the full-sized draught; also of the various curves likely to be given to the different parts of the body.
Before a workman could be trusted with the making of a body, he must of course have considerably advanced in the knowledge of his craft beyond the mere use of his tools, because the success of a carriage depends very largely upon the individual skill of the workman, more so than perhaps in any other trade.
The stuff is marked out from the thin patterns before mentioned by means of chalk, and in doing so care should be taken to lay the patterns on the timber so that the grain may run as nearly as possible in a line with it, and thus obtaining the greatest possible strength in the wood, which lies in the direction of the grain. Thus if the pattern be straight, lay it down on a piece of straight-grained timber; if the pattern sweep round, then get a piece of timber the grain of which will follow, or nearly follow, the line of pattern.
The strongest timber that can be obtained is necessary for the construction of the hind and front bottom sides; for the weight is directly transmitted to these, more particularly the hind bottom sides, where the pump-handles are fixed.
The body-maker, having marked and cut out the various pieces of timber he will require, planes a flat side to each of them, from which all the other sides, whether plain or curved, are formed and finished. They are then framed and scarfed together, after which the various grooves are formed for the panels and rebates, for the floor-boards to fit on to. Then, if there is to be any carved or beaded work, it is performed by the carver. Previous to being fitted in, some of the panels have strong canvas glued firmly on their backs, and when fitted in blocks are glued round the internal angles to give greater security to the joints, and to fix the panels firmly in their places. Before the upper panels are put in, the roof is nailed on, and all the joints stuck over with glued blocks inside. The upper panels are then put on, united at the corners, and blocked inside.
If the foreman who superintends all this be a thoroughly skilful artisan, and the men under him possess equal intelligence and skill, the work might be distributed amongst almost as many men as there are parts in the framework of the body. These parts will be worked up, the mortises and tenons, the rabbets and tongues, being all cut to specified gauges; and when they are all ready it will be found that they go together like a Chinese puzzle.
The woodwork being completed, the currier now takes the body in hand, and a hide of undressed leather, specially prepared for it, is strained over the roof, the back, and the top quarters of the body whilst in a soft pulpy state, and carefully sleeked or flattened down till it is perfectly flat. This sleeking down is a rather tedious process, and takes a long time and a great amount of care to bring it to a successful issue; when it is flattened down satisfactorily, it is nailed round the edges and left to dry, which will take several days.
Such panels as require bending may be brought to the required sweep by wetting one side and subjecting the other to heat, as of a small furnace.
The doors are now made and hinged, and the hollow spaces intended to hold the glasses and blinds are covered in with thin boards, to prevent any foreign matter from getting down into the space, and being a source of trouble to dislodge.
In constructing the body the aid of the smith is called in. His services are required to strengthen the parts subjected to great strain, more particularly the timbers forming the construction of the lower portion. All along each side of the body should be plated with iron; this should be of the best brand and toughest quality. It is several inches wide, and varies from ¼ to ¾ of an inch in thickness. This is called the “edge plate,” and is really the backbone of the body, for everything depends on its stability. It should run from one extremity to the other, commencing at the hind bottom bar, on to which it should be cranked, and ending at the front part of the front boot, bottom side. This plate should take a perfectly flat bearing at every point. Great care must be taken in fitting it, for although the plate may be of the requisite strength the absence of this perfect fitting will render it comparatively weak, the result of which will be found, when the carriage is completed and mounted on the wheels, by the springing of the sides, which will cause the pillars of the body to press on the doors, and it will be a matter of great difficulty to open them.
In the application of smith’s work to coach-building, it is often necessary to fit the iron to intricate parts while it is red hot, and if due precaution be not taken the wood becomes charred and useless, and in cases where there are glued joints it may cause the loosening or breaking of these joints and other material defects. It is an easy matter to have the means at hand to get over the difficulty. All that is necessary is to have handy some heat neutraliser. One of the commonest things that can be used is chalk, and no smith’s shop should ever be without it. If chalk is rubbed over the surface to which the hot iron is to be applied it will not char or burn. Plaster of Paris is a still more powerful heat neutraliser, and it is freer from grit. A small quantity of the plaster mixed with water, and worked up to the proper consistency, will be ready for use in about two hours. Many smiths will say that they never have any accidents in applying heated iron, but on inquiry the reason is apparent, for it will generally be found that such men use chalk, in order to see that the iron plate takes its proper bearings, thus inadvertently using a proper heat neutraliser. If it were more generally known that the difficulty could be met by such simple means, there would be less material spoilt in the smith’s shop.
It has been very common of late years for body-makers to use glue instead of screws and nails for panel work, &c.; but it requires a great deal of experience for a man to use glue with successful results. It is useless for the tyro to try it; he will only spoil the work. So, unless the artisan be well experienced in the treatment and application of glue, he had better leave it alone. To render the operation successful two considerations must be taken into account. First: To do good gluing requires that the timber should be well seasoned and the work well fitted. Second: In preparing for gluing use a scratch plane or rasp to form a rough surface of the pieces to be joined together, for the same purpose that a plasterer scores over his first coat of plaster-work, in order to give a key or hold. The shop in which the gluing is done should be at a pretty good temperature, and so should the material, so that the glue may flow freely. Having the glue properly prepared, spread it upon the parts, so as to fill up the pores and grain of the wood, and put the pieces together; then keep the joints tight by means of iron cramps where it is possible, and if this cannot be done the joints must be pushed tightly up, and held till the glue is a little set and there is no fear of its giving way. All superfluous glue will be forced out by this pressure and can be cleaned off.
A great cause of bad gluing is using inferior glue and laying it on too thick. Before using a new quality of glue, the body-maker should always test it by taking, say a piece of poplar and a piece of ash, and glue them together, and if when dry the joints give way under leverage caused by the insertion of the chisel, the glue is not fit for the purposes of carriage-building and should be rejected. With good glue, like good cement, the material should rather give way than the substance promoting adhesion. This is a very severe test, but in putting it into practice you will be repaid by the stability of your work.
It is often found that joints glued together will allow water to dissolve the glue, and thereby destroy its adhesive power. It may have been well painted and every care taken to make it impervious to water, but owing to its exposed position water has managed to get in. Often where screws are put in the glue around them will be dissolved, caused by the screws sweating; and it is very often found, where the screws are inserted in a panel, that the glue loses its strength and allows the joint to open, and there is little or no appearance of glue on the wood, which shows that it has been absorbed by the moisture.
To render ordinary glue insoluble, the water with which it is mixed should have a little bichromate of potash dissolved in it. Chromic acid has the property of rendering glue or gelatine insoluble. And, as the operation of heating the glue pot is conducted in the light, no special exposure of the pieces joined is necessary.
Glue prepared in this manner is preferable in gluing the panels on bodies, which are liable to the action of water or damp. The strength of the glue is not affected by the addition of the potash.
In plugging screw holes glue the edge of the plug; put no glue into the hole. By this means the surplus glue is left on the surface, and if the plug does not hit the screw it will seldom show.
Where brads are used the heads should be well set in; then pass a sponge well saturated with hot water over them, filling the holes with water. This brings the wood more to its natural position, and it closes by degrees over the brad heads. The brad must have a chance to expand, when exposed to the heat of the sun, without hitting the putty stopping; if it does it will force the putty out so as to show, by disturbing the surface, after the work is finished.