A practical treatise on coach-building historical and descriptive

by James W. Burgess

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.

Waterproof Glue.

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.