K. J. Adcock

When it is considered that the construction of machinery for the leather trade had barely started thirty years ago, the wonderful variety and utility of modern machines are remarkable, and it is a moot point whether engineering science has not played as great a part as, or even greater than, applied chemistry.

Excepting the bark mill, various kinds of tumblers, the fulling stocks, glazing and rolling machines, there were practically no efficient mechanical aids to lighten the exceedingly laborious operations incidental to leather manufacture two decades ago; but so many improvements have lately been made in the construction of machinery for practically every operation in the trade that most of the machines require very little skill to work them, and can be operated by intelligent youths after a few weeks' experience.

The change has been of great benefit to the health of the workers, for the continual stooping over beams and sloping tables, combined with the arduous nature of the work, was very injurious. The reputation that tanning had as a healthy occupation was due more to the work of the labourers than that of the skin workers. (The old-fashioned lime-yards and tan-yards were generally in the open, whereas modern tanneries are roofed.)

Leather trades machinery was not a success at first, probably because it was very difficult to get the necessary information from leather manufacturers. However, as the engineers gained more experience of the methods of leather-making, the defects were gradually remedied until it may be truly said that the machines now reach a high state of perfection. It was no uncommon thing for workmen to lose a finger or two in a machine, but such accidents are now rare, owing to improvements in the construction of the machines.

Most of the machines used in the leather trade are of the cylinder type, the raw skins or leather passing between two rollers, of which the upper one performs the operation while the lower one helps to draw the material through the machine. To prevent accidents and control the working of machines, a third roller is often used, which serves to "feed" the leather or skins to the working cylinders. Of this type of safety roller, the Seymour-Jones attachment to the shaving and buffing machine is of great importance.

Fig. 5

SHAVING CYLINDER

The operations of the tannery, which are performed by cylindrical machines, are dehairing, fleshing, scudding, samming, shaving, scouring, striking-out, setting, boarding, buffing, graining, printing, embossing, and blacking or colouring. The working cylinders usually vary according to the character of the operation, although one or two types may be used for at least three different operations.

Where cutting or paring is done, the working cylinder is fitted with brass blades, or steel blades backed with iron. The blades are spiral in some machines, and are so arranged that half of them converge to the left, and half to the right (Fig. 5). When in work, this type of cylinder not only performs the operation for which it is specially intended, but also stretches the leather outward, by reason of the arrangement of the blades or knives. The blades overlap one another to obviate marking, for if the blades met exactly at the centre they would make a line on the leather. Figure 6 shows another arrangement of knives for the process of buffing.

The most important machines outside the working cylinder type are the splitter, and the glazer. There are several kinds of splitting machines, but the band-knife machine (Fig. 7) is the most largely used. This is a veritable triumph of the engineer's art, for it is possible to make five or six layers, all about the same size, out of one hide, although leather is only split once or twice as a rule. Of course, sole, belting, and other thick leathers are not usually split. The invention of the belt-knife splitting machine revolutionised the leather trade, and there would undoubtedly have been a great shortage of leather without it. Formerly, all the levelling and reducing of substance was done by paring off quite small pieces with the shaving knife (Fig. 8), a difficult and laborious work. These parings were only suitable for pulping and compressing into leather board; but now the flesh splits removed by the machine can be curried, enamelled, printed, or rolled to make serviceable leathers, although, of course, not nearly so good in quality as the top or grain split. The main working part of the splitting machine is an endless steel knife which passes round two wheels placed at opposite ends of the machine. The leather is drawn to the knife through two rollers, of which the lower one is in sections to allow very thick parts of the hide to pass through the machine. It would need a large volume to describe in detail all the different machines used in the leather trade; the constructional details of only one machine can be given, and, in view of its importance, the shaver is selected. Reproductions of other machines will appear in succeeding chapters.

Nearly every leather trades' engineer constructs shaving machines, but the Howard-Smith is described here, not because it is the most popular (unfortunately there is a decided preference for low-priced machines), but because it is one of the best from an engineering point of view, and because several improvements are embodied in its construction.

This machine consists of nearly one hundred parts and each is made of the best material available. The advantage of this is obvious when the question of repairs is fully considered. The first Howard-Smith machine made has been running more than four years, and has not cost the owner a penny for repairs, beyond, of course, the expense of replacing the blades of the working cylinders; whereas it is no uncommon occurrence for a cheap machine to be thrown on the scrap heap after a few years' wear. It is always advisable, therefore, to buy machinery of the best grade.

Figure 10 represents a drawing of the shaving machine, A being the side view, and B the front. The work of the draughtsman generally appears to the uninitiated to border on the miraculous; he is often the designer and architect of the machine, and his work is certainly interesting and skilful.

Many of the heavy parts, such as main castings, pedestals, etc., are made in the foundry, which may be part of the leather trades' engineer's works if he is in a large way of business. The finer parts, those which might be termed the fittings, are made in the turnery department; while the machine is assembled in the fitters' shop.

Figure 10 A shows the side, and 10 B the front construction of the shaving machine. The figures indicate, by following the arrows, the principal parts of the machine, which are shown in detail in sectional tracings. For example, T. 65, of which no working parts are shown in the diagram of the complete machine, is reproduced in detail in a separate drawing shown in Figure 11. Each part of the machine is numbered and entered in a stock-book.

In describing the principal parts indicated in Figure 10, it will give an idea of the assembling of the machine if a beginning be made with the main iron castings. These comprise the main bed (64), two side frames (62), and the front frame (58). The side frames are strengthened by the ribs which form the edge, and which are about three times as thick as the body of the casting. The object of the front frame is to support the foot lever (59), the rocking frame (57) carrying the rubber roll (79), and the wooden roof (75) over which the leather is passed. The spring (76) pulls back the rocking frame (57) when relieved by the operator removing his foot from the lever (59). The long spring (77) lifts up the foot lever (59) when the latter is released.

The pullies (73) are connected with the knife cylinder which shaves the leather. The cylinder is obscured by the wheel-guard (65) and is, therefore, shown separately. This cylinder is comprised of a shaped piece of steel (turned out of solid metal bars of 4-3/4 in. diameter) into which spiral steel blades are caulked with copper or brass. When turned, the body of the cylinder is 4-5/8 in. in diameter, but the parts forming the bearings are reduced to 1-1/2 in. The number of blades is twelve, fourteen, or sixteen, according to the kind of leather shaved, and to the choice of the operator.

It is interesting to note that these blades are now being made in Sheffield, although, before the war, they had to be imported. The knife guard (65), shown in detail in Figure 11, is an ingenious contrivance which prevents the operator's hands being drawn into the machine. It consists of an automatic shutter worked by a steel chain from the foot lever. Figure 11 a represents the shutter closed down on the knife with the rubber roll, on which the leather is carried to the knife, at a safe distance from the shutters. Fig. 11 b shows the position when the machine is shaving the leather, the guard being clear and the rubber roll engaged with the knife.

In order to sharpen the blades of the cylinder, a carborundum wheel is fixed in close proximity, its position being indicated in the drawing by the wheel cover (67). A bracket for feeding the wheel to the blades when grinding them is shown at 66. When grinding the blades, the saddle (68) carries the wheel backwards and forwards across them. A special feature of the saddle in this particular machine is the double-thread screw, one a right hand, and the other a left hand. The saddle (68) is actuated by a "swimmer," as the makers term it, which engages, say, first the right-hand thread; when the saddle has travelled to the end of its movement the "swimmer" automatically enters the left-hand thread, and the saddle is rotated in the opposite direction. The "swimmer" can be disengaged instantaneously. A brush (55) is fixed near the cylinder to remove any leather shavings adhering to the blades. It also acts to some extent as a fan, and, by creating a current of air, carries the leather dust away from the operator. A trough is filled with water to catch the dust from the carborundum wheel, while the knives are being ground. The trough should be cleared out and refilled with clean water from time to time. It is essential that no dust from the grinding wheel comes into contact with vegetable tanned leather required in a natural or colour finish, otherwise it will cause iron stains, which are difficult to remove without damaging the leather. For this reason, the knives should not be ground while this class of leather is being shaved.

An important detail of the machine under description is a trueing device. Knives are often roughened owing to the carborundum wheel wearing irregularly. The trueing device keeps the wheel perfectly true by means of a diamond held in the end of a screw (78). Another ingenious arrangement (patented) is a spring (79a) placed at the back of the rubber roll (79), which enables the roll to spring back when the leather, or any part of it, is too thick for the cutting cylinder.

A unique advantage of the Howard-Smith machine is that it is ball-bearing throughout. The main driving shaft revolves on four massive ball-bearings in case (71). The pullies are firmly fixed to the driving shaft with keys or feathers. Afterwards the pullies are machined, so that the whole shaft with its pullies is perfectly balanced, and the machine runs smoothly without vibration.

The bladed cylinder is likewise mounted on four ball-bearings. The intermediate driving shaft (70), which is mounted on two ball-bearings, is connected with a large drum shaft (70a) which, in its turn, sets the carborundum wheel in motion.

Fig. 12 represents another make of shaving machine.