Part 22

Many makers have realised this and have devised very ingenious implements, some of which we reproduce, though we are obliged to limit ourselves to certain types, for they can be varied in countless ways according to the needs of particular cases. The same workman, as we have already said, may have several appliances which he uses in turn as he needs them in the course of his work.

These appliances are constructed in two ways; some are fixed to the end of the forearm and are immobile, some are attached by means of a joint or joints and are capable of rotation in various directions.

(a) Fixed Appliances.--We illustrate here an appliance derived from the simple hook, the vine-dresser's claw, devised some time ago by Gripouilleau; branches of varying size can be held while the other hand saws them or cuts them with the pruning shears (Figs. 163 and 164).

This appliance of Gripouilleau, with a series of hooks, forms the basis of almost all the "pincer hands" constructed by M. Boureau and characterised by--

(1) The closure of the upper hook which is thus transformed into a ring, the two appliances being combined in one;

(2) The spring fixed to the straight side of the hook providing the grip necessary for holding articles. If the free end of the spring is turned up like the pointed toe of a mediæval shoe a sufficiently large opening is left between it and the straight edge of the hook to enable an object which is fixed mechanically or held by the other hand to be pushed into and gripped by the spring.

The simplest type of this mechanism is the postman's hand (Figs. 165 and 166).

The left hand of the postman who sorts letters has for its work to keep in the proper order the envelopes which are arranged in little packets; the right hand has only to push the letter into place between a flat spring, fixed to the wrist, and the back of the hook. If two or three springs are supplied the postman can arrange two or three packets of letters at the same time. He can also bind the packet with string.

The vine-dresser's hand is provided with this spring to hold small flat objects, but the second spring is wavy in outline, so that semilunar spaces are left between it and the first. Into these branches slip when the spring is pressed against them, and they are thus held more firmly, whilst being sawn or pruned, than by the twisting action of the old pattern hook of Gripouilleau (Figs. 167 and 168).

This thrust to seize the branch is somewhat rough, and is only possible in holding hard wood which there is no fear of bruising. For more delicate shoots (grafting vines indoors, preparation of cuttings), a grip is necessary which can be opened before seizing hold of the object. This is accomplished by prolonging the spring towards the forearm as a handle, pressure upon which against the chest (when standing), or against the knee (when sitting), opens the grip, in which the graft, for example, is then placed in the opening of the correct size.

The packer's hand is very ingenious (Fig. 169). It has the hook pierced by an eye enabling a thread to be passed through a basket as with a curved needle. The jaws of the pincers are smooth at the tips, but further back they have a series of graduated notches in which tacks of different sizes can be held whilst they are driven in with the hammer. But of course a workman can only work quickly if he can hold a number of tacks of the same size in the palm of his hand, placing one under the hammer, relaxing his hold of it after the first gentle blow has fixed it, and getting the next ready while he drives it home.

The plumber's hand (Fig. 170) is made in the shape of a pair of gas pliers, and ends in cutting edges with which wires can be cut. With them a bolt can be held whilst the other hand screws on the nut.

The leather-cutter's hand (Figs. 171 and 172) should be able to hold the skin which the other hand cuts: it consists of a plate with a rough surface fixed to a ball and socket joint which allows it to turn in any direction, so that the other hand can follow the line to be cut which is often sinuous. This appliance may also be used to hold a drawing paper, a rule for cutting cardboard, or sheets of paper for binding.

The examples that we have chosen amongst Boureau's appliances for craftsmen will, we believe, be sufficient to explain the principles of their construction. These consist in studying the movements which are normally carried out by the passive hand (usually the left hand, but the right in left-handed people) and to devise an appliance accordingly, the sound hand always becoming the active hand.

We could have described many more examples, but we shall only say a few words about the mechanic's hand, which is simply an adjustable spanner which can be automatically closed, terminating in toothed pliers to hold circular objects without the necessity for being screwed up. As a matter of fact, in all the work of a mechanic (sawing, filing, drilling, tightening screws, hammering, forging, and grinding) the left hand is only used for picking up and steadying the article to be manipulated. M. Boureau rightly considers that it is better to entrust this rôle to the artificial hand rather than to contrive to make the latter capable of sawing or of filing by means of the devices which we shall describe further on (p. 121 and following), ingenious and interesting though these may be.

From these appliances, adapted to certain particular grips, others have been devised for chair caning, soldering, and for enabling factory hands to work starting levers and brakes.

Thus each case must be studied separately and the workman furnished with one or several appliances according to his needs, making the necessary modifications from the existing patterns.

Several of these appliances are attached by a ball-and-socket joint like that described for the leather cutter: this is an intermediate form between the fixed appliance and the jointed appliances which will be described later.

Boureau recommends that the length of the forearm should be such that the artificial appliance reaches only as far as the level of the sound wrist. The work will then gain in precision. We believe that this principle holds good even for the true artificial hand, which should be made 3 to 4 centimetres shorter than the sound hand. But it must be realised that we shall be met with a difficulty, which we have already experienced. Comments are made upon the appearance of the arm and the wearer may sometimes be made to believe that this is due to faulty construction.

For certain special crafts the subject may be studied from another standpoint and an actual tool constructed which carries out the necessary actions like a machine worked by the forearm, so that in these special cases the artificial hand is the active hand.

At the Valentin Hauy Institute for the blind, where there has long been a brushmaking workshop, we have seen in use a very ingenious tool of this description with a combined action for carrying out the entire manipulation of the thread which fixed the little bundles of bristles into the holes perforating the back of the brush. Results are so good that a blind and maimed worker using this apparatus works more quickly than his comrades who have the use of both hands. It consists of a two-pronged claw surmounted by a small thimble-shaped projection and with a small hook, like a crochet hook projecting in front (Fig. 173). The hook first passes through one of the holes in the back of the brush, catches up the thread and draws it through the hole (Figs. 174 and 175). The thread is then looped around the thimble, whilst the sound hand binds the little bundle of bristles into a twist of the loop (Fig. 176), and finally the bundle is fixed into the hole, the claw being used to draw the brush towards the worker (Fig. 177).

(3) In place of an actual tool the detachable part may consist of a clamp on the principle of a ring into which the tool is inserted by the handle. The two principal methods are the screw and the American chuck. A glance at figures 178 and 179 will explain how the large handle of a tool intended for heavy work is controlled by means of a screw and rings.

At Rouen we have seen the disabled Belgians who had been re-educated wearing an ingenious T-shaped clamp by means of which the handle of a tool may be held either in the line of the axis of the forearm or at right angles to this. This method is specially useful for manipulating a file which is worked with one hand while the other, in this case the sound hand, presses upon the free end. Usually the filing is done backwards and forwards, working from base to tip of the file, but sometimes, specially for final polishing, the file is held with both hands and worked from side to side.

The American chuck consists of a pair of metal jaws fixed at their base into a cylinder and appearing somewhat like the petals of a long corolla. Another cylinder is screwed over the first to control the opening and shutting of the jaws. When this cylinder is unscrewed the jaws open and the handle of the tool can be inserted, when it is screwed up it closes the jaws and makes them grip the handle.

The pincers are composed of two jaws with vertical cylindrical grooves (to fit upon a handle), joined above by a ring (Fig. 185) and coupled by a spring C which keeps them apart. The pincers fit into a piece B (Fig. 182) cut on the outer side with a screw thread (Figs. 182 and 183) upon which the piece A is screwed up or down (Figs. 180 and 181). When screwed towards the point of the pincers it presses on the two jaws and closes them. When screwed in the opposite direction the pincers open automatically.]

If the jaws open widely, the wooden handle of a tool can be held, but if the opening is small the unmounted tool must be fitted into them (Figs. 186 and 187). This method is specially useful for files, as it frequently happens that several files are required for the same piece of work and they can be changed rapidly.

It must, however, be insisted upon that the principle of giving a passive rôle to the artificial hand is to be preferred.

(b) Appliances with Mobile Joints.--In the course of work the direction of the wrist is changing at every instant, flexion, extension, pronation, and supination occurring, sometimes in order to move around the object, sometimes in order to maintain a suitable position when the movements of the shoulder and elbow vary the direction of the forearm.