The Plane and Spokeshave.
I have already made mention of the Plane in connection with the Chisel, and shown that, like that tool, it is formed on the same principle as the Rodent tooth.
The use of this important instrument in carpentering cannot be overrated, as is shown by the numberless varieties which are used by carpenters, and the different uses to which they are put, sometimes merely smoothing a level surface, and sometimes forming a “moulding” where ornament is required.
In principle, a Plane is a cutting edge or chisel, pushed along the object to be worked, and, the edge being guarded, taking off a very thin shaving from the surface.
On the right hand of the accompanying illustration is shown the Plane in action, with the thin shavings falling from it in curled masses. Perhaps some of my readers may have visited some of the great iron-works, and been struck with the use of the Plane as applied to metal instead of wood, long iron shavings being taken off as easily as if they were deal, and curling in just the same manner.
There is an instrument very familiar to carpenters, called the Spokeshave, on account of its use in trimming the spokes of wheels. Different as it may be in appearance, it is identical in principle with the plane, having an edge guarded by a piece of wood, so that the blade cannot cut too deeply into the object on which it is employed. The chief distinction, indeed, is, that the workman, instead of pushing the blade from him, draws it to him.
When shaving was more in fashion than it is in these more sensible days, there were many inventions to lessen the trouble, not to say the perils, of shaving. To use the razor in a hurry was anything but an agreeable occupation, especially if the weather were frosty, and the fingers so chilled that they hardly knew whether or not they had the razor between them.
In order to render this very unpleasant task less disagreeable, some ingenious individual invented the Guard Razor. The principal part of the invention consisted in a plate of metal sufficiently thin not to add materially to the weight of the razor, and sufficiently strong to resist a moderate amount of pressure. This was fixed along the blade of the razor in such a way that it just allowed the edge to show itself, and, in fact, converted the razor into a plane or spokeshave. The exact amount of edge which might be shown was regulated by screws, and the guard itself could be removed at pleasure, so as to allow of the razor being sharpened.
Now let us see if we can find any examples of the Plane or Spokeshave in Nature.
I trace at least one example of the Plane in the insect world. More than a hundred years ago, that very observant naturalist, Gilbert White, noticed a bee performing a curious task. She was running up the stem of the garden campion, holding her jaws extended, and stripping off the down with all the dexterity of a hoop-shaver. She collected a bundle nearly as large as herself, and then flew away with it. What she did with her burden he knew not, but the history of the insect has been told fully, though briefly, by Mr. F. Smith, in his “Catalogue of British Hymenoptera:”—
“Although the species belonging to this genus are numerous, and are found both in the Old and New World, there is only one found in this country, Anthidium manicatum; this is truly a summer bee, not making its appearance before the latter part of June or beginning of July.
“This insect, so far as my own observation has enabled me to ascertain, does not construct its own burrow, but makes use of any hole which is adapted to its purpose. I once detected a bee entering the hole above the wheel of the sash-line in a summer-house; but its nests are most commonly formed in the holes bored in old willow stumps by Cossus ligniperda (the Goat-moth): formerly they were easily obtained in Battersea Fields, where the willows abounded.
“It is probable that when the parent insect has selected one of these ready-formed tunnels, she enlarges the end used as the depository of the nest, and this is easily effected, as the stumps in question, at the depth of a couple of inches, consist of soft decayed wood.
“The chamber being formed, the bee collects a quantity of down from woolly-stemmed plants, with which she forms an outer coating. She then constructs a number of cells for the reception of the pollen, or food of the larva; they consist of a woolly material, mixed with some glutinous matter which resists the moisture of the food they contain, and in which the larva, being full fed, spins a brown silken cocoon. These bees pass the winter in a larva state, and do not appear until midsummer.
“In one respect, the sexes of this genus differ from most other bees, the males being much larger than the females.”
The reader will see from this account how exact is the analogy between the carpenter’s plane and the jaws of the bee. In consequence of the simile employed by Mr. White, the insect has been popularly known by the title of the Hoop-shaver Bee. It is a tolerably common insect, and abounds in the South of England.
TOOLS.
CHAPTER II.
THE SAW AND ITS VARIETIES.
Cutting Tools and their working.—Structure of the Edge.—The Kris.—Edge of a Razor.—The Sword and the Apple.—Australian Saw.—Fretwork Saw.—Various Saw-flies.—The Pioneer’s Saw.—Cutting Tools of Trichiosoma.—Side Teeth of the Saws.—The Cordon Saw, or Band Saw.—Tooth-ribbon of Whelks, Slugs, and other Molluscs.—The Dog-whelk, or Purpura.—The Circular Saw.—Sawyer-beetles and their Mode of Work.
STILL keeping to the Cutting Tools and their varieties, we come to the Saw, i.e. the cutting tool set with teeth upon its edge. Now, in plain fact, there is no cutting instrument that does not more or less partake of the character of the Saw; for, in the first place, it is absolutely impossible for man to grind an edge so fine that, when magnified, it will not appear to be deeply notched, and, in the next place, its cutting powers are greatly due to the notches and teeth, and the direction of their points.
We will take both these subjects in turn.
First, as to the notches, or serrated edge. I have now before me two instruments, each the best of their kind, and in both of which the serrations are essential to efficacy. The first is a Malayan dagger, or “kris,” and the second is a surgeon’s lancet, made by Ferguson, of London.
In the kris the edge is intentionally serrated, having been eaten away by means of acids until the required effect was produced. The Malayans know by experience that such an edge is most deadly in a weapon, and that it will cut certain vital parts which a smoother edge might pass without doing any damage.
Now we will take the lancet, and put it under the microscope, when it assumes the most curious resemblance to the kris. Its mirror-like surface looks as if it had been very roughly treated with a coarse file, while its thin and delicate edge, which is perfectly smooth to the eye, and which will pass through a piece of stretched wash-leather without any apparent opposition, becomes as rough and jagged as that of the Malayan weapon.
Take even, for example, the common butcher’s knife, which is perpetually being sharpened on the “steel” that hangs at his belt. The reader may observe that the butcher does not rub the blade of his knife backwards and forwards on the steel, as unskilful persons do. Rapid as is the movement gained by constant practice, any one may see that the blade is always moved in one direction, so as to force the microscopical teeth to point one way, and so to act as a saw when the knife is drawn across the meat.
The power of these teeth or notches may be inferred from a well-known fact. If a razor, no matter how sharp, be pressed upon the human skin without any “draw,” it will indent the skin, but not cut it, while the slightest drawing movement will cause a deep wound. It is the knowledge of this fact that enables an expert swordsman to sever an apple placed on the palm of the bare hand, without even scratching the skin. I have witnessed this feat, and at once saw that it was due to the absence of any “draw” to the cut. The apple was laid on the palm of the hand, which was opened as widely as possible, so as to flatten it. The sword was then brought down on the apple with a sort of chopping movement, so that, although it indented the skin, it did not even inflict a scratch.
By the use of the “drawing” movement, the same sword severed a gauze veil laid across it, the two halves floating in opposite directions. By the same cut, I have seen some astonishing feats performed with an Indian sword now in my collection, the objects of attack falling asunder as if by magic, without any apparent force being used.
Having now glanced at the principle of the Saw, we will proceed to some of its details.
The simplest form of Saw in existence is that which is in use among the Australian natives, and consists of obsidian flakes set along one side of a stick. It looks a rude and inefficient affair enough, but it can cut better than might have been thought, as I can testify from experiments on such a saw in my collection.
Many as are the varieties of the Saw, the principle is the same in all, and the chief distinction lies in the shape and arrangement of the teeth, according to the work which they have to do. Watch-spring Saws, for example, which have to cut metal, have their teeth so slight as to be hardly perceptible, and arranged nearly in a line with each other. The Fretwork Saws, which have to cut delicate patterns in wood, with the slightest possible waste of material, are of the same character. Then we have the long curved teeth of the Circular Saws, which tear their way savagely through great tree-trunks, and fill the air with clouds of sawdust. There are also the Tenon Saw, with its thin blade and broad back; the pioneer’s saw for cutting green wood, with its double array of teeth, so as to make a wide “kerf” in which it shall not be clogged; together with many others that we cannot enumerate here.
We will now examine some Saws as found in Nature.
I need scarcely say that some of the best examples of natural saws are furnished by those insects which are known to entomologists as Tenthredinidæ, and to the general world as Saw-flies. These insects are supplied by Nature with a pair of most remarkable saws, which aid them in depositing their eggs. Indeed, without these instruments, the whole race of Saw-flies would long ago have become extinct.
They haunt almost every kind of tree and many plants, and one valuable plant, the Turnip, is so devastated by them, that whole crops are sometimes swept away. As, therefore, the knowledge of the life-history of any insect will tell us whether to protect or destroy it, and the best method of adopting either course, we will cast a hasty glance at some of our commonest Saw-flies, the instruments which they employ, the mode in which they use them, and the analogies between them and the saws made by the hand of man.
In the first place, it must be observed that the use of these saws is to cut grooves in young bark, these grooves being the depositories of their eggs. It follows, therefore, that as a tolerably wide groove is needed, the saw-blade is a tolerably thick one, and the teeth set on the same principle as that which is employed in the saw-sword of the pioneer. When the microscope is applied to the cutting instrument of the Saw-fly, it reveals the fact that there are two horny saws, which work alternately in their grooves, and that they are strengthened by a thick plate of horn on their backs.
The system of toothing is very complicated. Not only are the sides as well as the edges of the saws toothed, but each tooth is furnished with smaller teeth, after the fashion of the shark’s wonderfully effective cutting apparatus. These subsidiary teeth vary greatly in shape and size according to the species, and in some cases each tooth is quite a complicated structure. In Trichiosoma lucorum, for example, a bee-like insect, very common upon hawthorn, the teeth are extremely beautiful. It is difficult to describe them without diagrams, but I will try to give the reader an idea of them.
Each tooth is somewhat of a lancet shape, but is not terminated by a single point. At the tip comes the secondary tooth, which is conical and stands on a footstalk. The cone, however, is not simple, but is made of some seven or eight cutting plates, each smaller than its predecessor, and the last being a sharp conical point. The reader may imagine how effective such a saw would be in cutting green wood, the toothed sides and the subsidiary teeth alike preventing the blades from clogging, while the alternate movement of the saws enables them to do double work in the same time.
Mr. Westwood, who examined these insects very closely, throws out, in his “Modern Classification of Insects,” the idea which forms the subject of this book. Writing of the cutting weapon of the Saw-flies, he remarks that “from its admirable construction it cannot be doubted that a careful examination of its various modifications might furnish ideas for improved mechanical instruments.”
Mr. Gosse, in his “Evenings at the Microscope,” points out that, beautiful and elaborate as these instruments are, they are but the sheaths of a still finer and more delicate pair of saws. These secondary saws have only a few teeth on the edge, and these near the point, whereas the sides are furnished with a number of sharp blades, set on their edges, slightly overlapping each other, and directed backwards. There is a similar structure on the ovipositor of the Sirex, as we shall see when we come to treat of Boring Instruments.
Although the saws are made expressly so that they shall not stick in the wood, there are many instances known where female Saw-flies have been found dead on the branches, their saws still in the last groove which they have cut. I am inclined to think that these must be females which have deposited all their eggs, and which have died, as do nearly all insects under similar circumstances. This opinion is strengthened by some observations made by Mr. J. K. Lord on the Cicada, the female of which is furnished with a similar ovipositor:—
“I was curious to watch the female depositing her eggs.
“She first clasps the branch on both sides with her legs, and with the ends of the file very carefully slits up the bark. Then, placing the instrument longitudinally, she files away until she has obtained sufficient length and breadth. The small teeth of the files are now used crosswise of this fissure, until a trench is made in the soft pith.
“When large enough, slowly down the groove in the centre of the instrument glides a small pearly egg, pointed at both ends, and so transparent that the little grub within is clearly discernible. Gently she lays it within its bed, and then drops a thin gummy material on it, to secure it from moisture. This finished, she proceeds to deposit another, and so on, until a sufficient number are produced to fill the fissure; then over all she drags the everted bark. It is easy to perceive where the Cicada has been concealing her brood, by the elevation on the branch.
“In this manner she deposits about seven hundred eggs, going from branch to branch, her marvellous instinct teaching her to select the most suitable wood for the purpose. The time occupied in constructing each nest was from fifteen to twenty minutes. Her earthly mission finished, she drops, fainting and exhausted, from the branch, and dies.
“The male, who is always trilling his refrain, goes on, indifferent, or unconscious, that the task of his faithful spouse is finished, singing even, until his time comes—then he too drops beside her. Thus the songs one by one cease,—not only the Cicada’s, but all the forest choir, and give place to blasts that sigh in mournful music through the leafless trees.”
The Sirex and several of the larger Ichneumon-flies are often found dead in like manner, and I have no doubt from the same cause. An elaborate description of the beautiful double saws of the Cicada is given by Mr. Westwood in the work already quoted, together with illustrations.