Page:Encyclopædia Britannica, Ninth Edition, v. 11.djvu/461

Rh tap, which bears on its surface the counterpart of the required thread, so that by successive cuts it produces a helical groove of the correct form and depth. Such a tap (S) is represented in the en graving, together with a diagram of its cross section, showing the three cutting edges by which the screw thread is formed. Three such taps constitute a set for any one size of screw, the first being known as a taper, the second as an intermediate, and the third

Fig. 6. as a plug-tap, this last being almost parallel throughout. By a reverse process with dies fixed in a stock (T, fig. 6) external screws are cut, the particular form shown being the improved pattern of Sir J. Whitworth, who has done much to correct the faults of the earlier screwing tools. Screw plates, however, some of which can not be regarded as cutting tools at all, are still much used for small and fine screw threads. Cutting pliers and cutting nippers (U) have a pair of knife edges so arranged as to work exactly opposite to one another, the handles, on being tightly grasped, affording sufficient leverage for these edges to be forced to a short distance into the two opposite sides of a nail or wire, which, if of small diameter or of soft metal, can thus be cut asunder. Tube-cutters are an ingenious device which the extensive use of wrought-iron tubing for gasfitting has rendered necessary. They effect their object by cutting a groove round the tube to a sufficient depth to enable it to be fractured at the desired point. 3. Stone and hard materials cannot in general be treated by cutting tools simply with hand pressure, though some of the softer kinds of stone are carved with chisels used almost or altogether without im pact, and are sawn with toothed saws resembling the cross-cut saws ised for wood. Glaziers diamonds were till recently the only tools for producing the peculiar &quot;cut&quot; requisite for starting the clean- fracture by which sheet glass is divided, theirs, however, being a case of fissure rather than of true cutting. But of late years steel glass cutters have been introduced which act as long as the sharp ness of their edges is maintained in a manner precisely similar. In one form of these glass cutters (V) a cast-iron handle carries at its extremity a small freely revolving wheel of carefully hardened steel, round the circumference of which is the cutting edge, which can be sharpened on an oilstone when necessary. The so-called cut is produced by simply running this with a light pressure over the sur face of the glass. Diamonds, however, are used for cutting glass, stone, &c., by actually detaching their particles ; writing diamonds and diamond drills have this kind of action. II. Hand-tools without cutting action. With the exception of hammers and a few tools which are dependent on impact, such as cleaving wedges amongst wood tools, and embossing and similar punches amongst those for metal, tools of this class play in general only a subsidiary part to some cutting or other process. Amongst those used with pressure which cannot be considered as auxiliary may be instanced draw-plates, with which wire is made by drawing it through holes of conical form and of successively smaller diameters till the required size or &quot;gauge&quot; is reached; and burnishers, which reproduce on metals softer than themselves their own highly polished surfaces. Both of these act by inducing a flow of the metal under treatment for which, when it is not effected by impact, great force is required in proportion to the extent of the action. Metal shears and cutting punches of all kinds have been omitted till now, as their mode of operating cannot be regarded as true cutting from our point of view. It may be more correctly described as tearing, more or less completely localized accordin&quot;
 * o circumstances. The ordinary sheet-metal shears (W) merely

semble very powerful scissors, and, their action being quite local, they serve well for dividing the plates or other thin sheets for which alone they are suitable. Block shears (X) act with additional leverage, and can consequently be used for rather thicker metal the upper bow being replaced by a long straight handle, and the lower one by a stake which can be firmly fixed in a block of wood or otherwise. _With these the tearing action begins to be apparent, though its imperfection is of no great importance with the thick nesses of metal capable of being treated by any hand shears (for some tools ol this class, which by hydraulic or other means accumulate the power of one man to a sufficient extent to operate on bars or plates of comparatively great substance, are machines rather than hand tools, and in their case the mere slowness of the operation produces better results than would otherwise be obtained). Tho same may be said of the various punches used in combination with dies or bolsters, as in the punching bear (Z), of which the action exactly resembles that of shears, the punch taking the place of the upper blade, and the bolster that of the lower one. Of subsidiary tools (figs. 7) the vice is an absolute essential for the generality of metal workers. The ordinary tail-vice (a) used by mechanics has not yet been largely superseded, though many ingenious arrangements have been devised for remedying its main defect, viz., the want of parallelism in the movement of the jaws. The English parallel vice (/3) has not this objection, but its construction is not good mechanically, and it is but little used except for small work. In some patterns of vice, jaws are provided with a horizontal adjustment so as to grip tapering or other irregu lar forms, and in others the whole body of the vice can be swivelled

Fig. 7. cither vertically or horizontally. Hand-vices are used in the manner implied by their name, without being attached to a bench like the foregoing. An ingenious form of hand-vice (y) is shown in fig. 7. The screw wrench (5), which is used for turning nuts, &c., of various sizes has of late been deservedly the subject of various improvements in which weight is sought to be saved without sacrifice of strength ; and the shifting spanner, of which the duty is the same, has led to the exercise of much ingenuity without any perfectly satisfactory solution of the problem how it may best be constructed. The merit and simplicity of the ordinary screw driver, on the other hand, are well known. Instances of tools which afford a powerful grip by simple means are the blacksmith s tongs (e), the vice-chop tongs (f), the pliers (77), and the pincers (3-). A very powerful modification of the last-mentioned tool has lately been introduced into use under the name of the nail-puller (j). With this ingenious instrument very largely increased leverage is obtained, and the pull is given in a direction much more advantageous to the attainment of the de sired object. (C. P. B. S.)  HANG-CHOW-FOO, a of, in the  of , about 2 s north-west of the , at the southern terminus of the , by which it  with. It lies about 100s south-west of, in 30° 20′ 20″N. and 120° 7′ 27″E. Towards the west is the Si-hu or &ldquo;Western Lake,&rdquo; a beautiful sheet of, with its and s studded with s, s, and s, and its surface traversed by gaily- pleasure s. To the  it is a very. Exclusive of extensive and flourishing, the has a circuit of 12s; its s are well- and clean; and it possesses a large number of es, public s, s, s, and s. It has long ranked as one of the great centres of   and. In the   alone were said 