Page:Encyclopædia Britannica, Ninth Edition, v. 11.djvu/459

Rh It should be observed that the term &amp;lt;f cutting &quot; is applied to processes which have but little in common, the great differences of structure in the materials operated upon demanding equally great differences in the modes of effect ing the desired end, which is in almost all cases the forcible separation of their partMes in some regular and definite manner. If we regard, for example, the action of a sharp knife upon a piece of chalk as one of true cutting, i.e., the separation of its particles by the forcible insertion of a wedge-like blade of superior hardness to itself, we shall find that in by far the larger proportion of instances this simple action is rendered complicated, either through the substance under treatment being insufficiently compact to afford in itself the necessary resistance, or through its want of homogeneity causing a tendency in it to part more readily in some directions than in others. Thus all kinds of wood and the generality of both vegetable and animal substances, being cellular or fibrous in their structure, offer so much less resistance in a direction parallel to their fibres than in one transverse to them that in the former case many of them may be parted by fissure without any true cutting at all. So also with crystalline materials as is beautifully exemplified by the diamond, which lends itself to cleavage in certain planes in the most perfect manner, though the steel chisel which is employed for the process is very much inferior in hardness to itself. Metals also are frequently not homogeneous ; indeed they are sometimes said to be fibrous in structure, but it is only to a very limited extent, if at all, that they are so, and their great natural tenacity even then prevents the separation of their particles except by a true cutting process. Lastly, some stones and minerals, such as sandstones, are said to be cut, though they are formed of material consider ably harder than the tools which nre used upon them, the fact being that their hard particles are not cut at all, but are merely separated from one another when the cementing material which holds them together is compelled to give way. I. Cutting or Edge Tools. These, the term &quot;cutting&quot; being thus qualified, are mainly of two classes (i.) cutting tools used with impact, and (ii. ) cutting tools used mainly with pressure. These again may be subdivided into tools used (1) for wood and soft materials, (2) for metal, and (3) for stone and hard substances. i- 1. Wood-tools cutting by impact comprise all the varieties of axes and adzes, such as the ordinary English pattern of carpenter s a FIG. 1. Axes. axe_(a, fig. 1), the woodman s felling axe (b), the wedge axe (c) (which was one of the first American improvements in edge tools introduced into Europe), and the shipwright s adze (d), which last FIG. 2. Chisels. is a particularly rapid and efficient tool in skilful hands. All these when used in the direction of the grain of the wood act by cleaving rather than by cutting, except when the thickness of the chip 437 removed is so small that its tranverse strength is inferior to the lateral tenacity of the fibres. So also do chisels and gouges when driven by blows from a hammer or mallet. The ordinary mortice chisel (e, fig. 2) and the socket chisel (/) are specially adapted for being used in this way. 2. In the case of metals their hardness in general almost precludes the possibility of employing upon them any tools corresponding to the above. If we except a few special tools such as plumbers knives, &c., chisels will be found to be almost the sole representatives of this class. A blacksmith s chisel (g) held in a hazel withe, and used for hot iron, and some common forms of chisel for chipping it cold are shown in fig. 2, these being known as a chipping chisel (h), a cross-cut (j), a diamond point (Jc), and a round-nose (I). 3. Tools of this class for stone also consist chiefly of chisels, the mason s chisel (m) varying greatly in width of edge according to the variety of stone and the depth of the cut to be taken. Frequently they are brought quite to a point like the mason s pick, when they cease to be cutting tools from our point of view. The jumper (M), employed for rock drilling, with which the hole is produced by means of successive cuts radiating in all directions from its centre, which are delivered with the impact due either to its own weight or to the blows of a hammer on its outer end, is also a form of chisel. ii. Edge tools operating by pressure. Of this class the ordinary clasp-knife is perhaps the best known example. A sharp knife serves well for showing the different kinds of treatment by cutting or by fissure to which any particular wood or other moderately soft material is capable of submitting itself. The &quot;thickness&quot; of the cutting edge, or in other words, the angle which the inter secting planes which include it form with one another, the degree of smoothness or roughness of edge which best effects the clean division or separation of the fibres, and the possibility or other wise of producing a smooth surface by &quot;scraping,&quot; can all to a great extent be judged of with the aid of a knife. And the sub ject is by no means an unimportant one. Consideration of the action which takes place at the edge of a cutting-tool, and the strain which this action produces on particular portions of it are frequently of service in enabling us successfully to meet the special c-ses which arise in practice, and may sometimes guide us towards remedying the defective action of the hand-tools in use for ordinary work. America has long taken the lead in originating thoughtful improve ments of this kind, and the result is apparent in the rapid manner in which the use of edge tools and appliances of American patterns is now everywhere extending. 1. In fig. 3 are shown a few of the ordinary English wood-tools. They include the firmer chisel (o) used by carpenters, and a carver s chisel (p) and gouge (q}. A wood-engraver s scooper (?) and knife (s) are examples of special tools, being intended only for cutting hard wood in a direction transverse to the grain, cross-cut blocks of box wood being alone used for the finer kinds of wood-engravings. The spoke-shave (t) affords a good example of what has just been said as to the result obtainable by a well-directed effort towards the improvement of an old established hand tool. In the form figured (t), which is the ordinary one in use in England, the blade or &quot; iron&quot; is rather complicated in shape and is not very easy to sharpen; FIG. 3. Chisels, planes, and saws. each successive sharpening moreover impairs the efficiency of tie tool by widening the &quot;mouth,&quot; the unequal wear of the wood&amp;lt; n sole, which very speedily takes place, having also a similar effect. Thus three essential conditions of a good cutting-tool, viz., constant maintenance of its proper action, durability of the parts exposed to wear, and facility in sharpening are all unfulfilled. On the other hand those manufactured in America fulfil them admirably ; iron is substituted for wood as the material for the sole and handle, and the blade, which is merely a piece of flat steel, is firmly held in its place by a set screw, half a turn of which at once releases it. Planes are to be met with in great variety, the most usual for ordinary carpentry being the jack plane (u), the trying plane, and the smoothing plane (v). Of these the first is used for tak ing oif the rough, or for reducing the thickness of a board ; the second, which resembles it, except in being of much greater length, for correcting inequalities of the surface ; nnd the third, as its name implies, for the final smoothing. Planing bring