A practical treatise on coach-building historical and descriptive

by James W. Burgess

An axle, or an axletree, for a locomotive wheel vehicle, is that portion of wood or metal, or both combined, which serves as the axis or centre for the wheels to turn round on.

The name axle-tree at once indicates the substance originally employed for it, viz. wood. Axletrees are of two kinds; those which are fixed firmly in the wheels and revolve in gudgeons beneath the wheels, and those in which the wheel moves independently of the axle. The former, as being the rudest, was probably the first kind used. The earliest fixed axletrees were simply pieces of hard timber, with the ends rounded down into a conical form, that form being the easiest to fit to the wheel. Subsequently they were plated with iron to resist wear.

In the earliest iron axles the conical form was still preserved, for the obvious reason of easy adjustment to the wheel. These iron axles were not made in a solid piece, but were merely short ends bedded in and bolted to a wooden centre. Examples of these axles may still be seen in heavy carts and waggons.

The next improvement was to make the axles of a single bar of iron, and this practice has now become common. An axle is technically divided into three parts—the two arms, or extremities, on which the wheel revolves, and the bed, or that portion which connects the two arms together. The commonest axles, which are manufactured for the sake of greater cheapness, are formed of a square bar simply rolled to shape between mill rollers. This iron is uncertain in its quality, as it is liable to have sand cracks, blisters, and other imperfections, which cause axletrees when made from it to break down under strong concussion. To guard against this, the best axletrees are formed of several flat bars or rods of iron welded together in a mass; this is technically called “faggoting.” If you wish to discover whether an axle has been made in this way heat it to a red heat, and if it has been faggoted the grain or lines of the rods of iron running in different directions will be plainly discerned. The size is regulated by the weight it is intended to carry.

For a very heavy coach from 2 to 2¼ inches in diameter and 10 to 11 inches long in the arm is a fair size. For light carriages, both four and two-wheeled, 1½ inches in diameter and 8 inches length in the arm is a common size. Occasionally some are made as small as 1¼ inches in diameter. It should be remarked that a less size of axle would perform the work required of it if it were stationary, as in mill-work; but for locomotive vehicles it is necessary to provide against the greatest concussion they can meet with in ordinary application.

When iron axles were first used it was customary to drive an iron ring or hoop, 2 or 3 inches broad, into either end of the nave, to prevent too rapid wear. This plan is still used occasionally in heavy carts, but otherwise axles are always fitted with iron boxes, adjusted to the arms with more or less accuracy, according to the price and the material used for lubrication. For the prevention of friction in wooden axles soap or black-lead is the best materials; for common, coarse axles, a thick unctuous grease is the best adapted; but for axles that are accurately made and fitted to the boxes there is no lubricating material equal to oil of the purest kind which can be prepared, i.e. freest from mucilage or gelatine, according as it may be of vegetable or animal production.

The commonest axles now used are of a conical form, with a box of plate iron fitted to them. This box is made by welding the two edges of the iron together in a broad projecting seam, which helps to secure it to the nave. The inside of the box is sunk into hollows for the purpose of holding the lubricating grease. At the upper end of the arm the axle is left square, and against this a large iron washer is usually shrunk on hot. Against this washer the box works. To secure the wheel against coming off a small iron collar is placed on the reduced outer end of the arm, and a linch-pin is driven through the arm beyond it.

An improvement on this kind of axle is when the collar at the upper end or shoulder is made solid by welding, and a screw nut with a linch-pin through it is substituted for the collar and linch-pin. These nuts are commonly made six-sided, with a mortise or slot for the linch-pin through each side, in order to afford greater facility for adjustment. In all other particulars this axle is the same as the last, except that it is occasionally case-hardened to prevent wear and friction.

In travelling, these axles require to be fresh greased every two or three days, and the trouble thus caused is very considerable, besides the risk of omission, in which case the axle is likely to be entirely spoiled.

The commonest kind of oil axle is called the “mail,” because the peculiar mode of fastening was first used in the mail coaches. The arm is not conical, but cylindrical, in the improved kind. At the shoulder of this axle a solid disc collar is welded on for the box to work against. Behind this shoulder collar revolves a circular flange-plate of wrought iron, pierced with three holes corresponding with holes in the wheel from front to back, through which long screw-bolts are driven, and their nuts screwed sufficiently tight against the circular flange-plate to allow easy motion. The wheel, when in motion, thus works round the shoulder collar, while the flange-plate secures it against coming off. This is not neat or accurate, but it is simple and secure, and no nut or linch-pin is required to the axle in front, while the front of the nave can be entirely covered in. When screwed up for work, a washer of thick leather is placed between the shoulder collar and the box, and another between the shoulder collar and the circular disc, which extends over the whole surface of the back of the nave. The box of this axle is of cast iron. The front is closed with a plate of metal, between which and the end of the axle-arm a space is left of about 1 inch as a reservoir for oil, which is poured in through a tube passing through the nave of the wheel and closed by a screw pin. At the back of the box there is a circular reservoir for oil, ¾ inch in depth and ½ inch wide. When the wheel is in motion the revolving of the box keeps the lubricating material in circulation between the two reservoirs; any portion getting below the arm at the shoulder gradually works its way out and is wasted. The oil in the back reservoir does not waste by leakage so rapidly as that in the front; but when the leather washer becomes saturated with water the oil is liable, by reason of its lightness, to float on the water in or about the washer, and thus get wasted.