Sol 



SCREW MANUFACTURE. 



SCRIBES. 



used together) out of the mould, so as to leave the impreasion of the 

 thread uninjured. 



Screw-bolts and other screws for working in metal are manufactured 

 in a similar manner to those for working in wood, when the number 

 required is sufficient to justify the expense of adjusting the machinery. 

 When this is not the case, they are, if small, often cut by hand, without 

 the aid of a lathe. The die, or instrument for cutting an external screw, 

 resembles a common nut, but is usually divided into two parts, which 

 are fitted into an iron stock or die-frame, with long handles. Notches 

 are cut in the die, across the direction of the threads, in order to pro- 

 duce cutting angles, and to afford room for the escape of the portions 

 of metal removed in cutting the worm. The die, which is formed of 

 steel, and well tempered, is inserted in the die-stock, with its two 

 halves a little distance apart, but capable of being brought together by 

 regulating screws fixed in the die-stock. The bolt to be made into a 

 screw is fastened in a vice, while its end is placed in the die. The 

 operator then proceeds to turn the die-stock, so as to worm the die on 

 to the bolt ; not by a continuous motion in one direction, but by a 

 series of turns backwards and forwards. When the die has proceeded 

 as far as the worm is required to extend, it is taken off, screwed up a 

 little closer, and again applied in the same manner ; the process is 

 repeated, closing the die a little after each operation, until the worm is 

 cut to the required depth. In working a similar apparatus by 

 machinery, the dies are sometimes made in four pieces, the die-frame is 

 stationary, and the bolt or screw-pin itself revolves. In this case the 

 rotation is continuous, but in other respects the operation resembles 

 that described. In cutting large screws, especially with a square 

 thread, a steel cutter is sometimes used with the die, whether turned 

 by hand or fixed in a Lithe. Very small metal screws are cut by a 

 steel tap-plate, wormed and notched in a similar manner to the dies 

 above described, but having several holes varying slightly in size ; the 

 worm being formed progressively, by using at each operation a smaller 

 hole than at the preceding one. 



Hollow or interior screws are commonly cut by means of a steel tap, 

 which is simply a screw of which great part of the worm is removed 

 by filing Hat faces along its whole length, the angles left 4>y this 

 operation forming a series of obtuse cutters. The head of the tap is 

 squared, to fit into the middle of a long handle, by which it can be 

 turned with considerable purchase. The tape for cutting screws in 

 wood are commonly fluted on the sides, to make them cut the more 

 readily, and to afford more room for the escape of the cuttings. The 

 top invented by Mr. Jones answers the purpose of a tapering tap for 

 commencing the screw, and a cylindrical one for completing it : the 

 )>art being tapered, while the upper is left cylindrical. The tap 

 is shown at c, more adapted for cutting than either a or b, which are 





the more usual forma. In large taps of this kind a steel cutter may 

 be inserted, as shown in the section d, at the commencement of the 

 cylindrical portion of the tap ; the cutter being made to project a little, 

 so that the tap follows it without difficulty. An ingenious kind of tap 

 (or cutting a square-threaded screw consists of a hollow screw of steel, 

 having a hole drilled obliquely from the front end of the thread to the 

 hole in the centre of the tap. The edges of this oblique hole, being 

 made sharp, cut their way through the wood when the tap is turned 

 round : while the hole itself forms a channel by which the cuttings 

 escape into the cavity in the centre. For cutting internal screws in 

 wood, where great accuracy is not required, the tap invented by Mr. 

 Siebe, represented in the following cut, is useful. Though the wooden 

 [art is cylindrical, the steel plate topers towards the end that enters 

 the hole, in order that, by the first teeth projecting but little, the 



instrument may cut gradually. A groove is cut on each side of the 

 top, where the plate is inserted, to afford room for the escape of the 

 cutting* ; and the upper end of the cylinder is made flat or square for 

 the purpose of fitting the lever by which it is turned. 



The large iron screws used in vices, presses, waggon-jacks, &c., are 

 formed by means of dies, turned with immense power by very long 

 levers; the thread being made without cutting, by indenting and 

 squeezing up the metal. In the ordinary method of cutting screws in 

 a lathe, the size of the worm, or the distance between the threads, is 

 regulated by a pattern screw, and cannot be varied from it. An 

 ingenious machine is used in the Woolwich dock-yard for cutting a 

 great variety of different screws from one pattern. 



In making screws for mathematical or astronomical instruments, 

 where the greatest accuracy is essentially necessary, it is especially 



362 



desirable to avoid the risk of error arising from irregularities in the 

 pattern screw, or in any part of the machinery used. The late Mr 

 Holtzapffel was highly skilled in this art; but Mr. Whitworth has 

 recently carried it to a degree of refinement never before atUined 



SCREW-PILE. [PILE ENGINE.] 



SCREW-PRESS. This machine offers great facilities for the appli- 

 cation of power ; as the force applied may be almost infinitely multi- 

 plied by increasing the length of the lever by which it is turned, and 

 diminishing the distance between the threads. It is also very convenient 

 in cases where a continued pressure is required ; because, in ordinary 

 cases, the friction of the screw is too great to allow it to run back on 

 the removal of the power by which it is turned. In the common 

 screw-press the articles to be pressed are laid upon a stationary bed, 

 forming the base of a strong frame, in the upper cross-bar or head of 

 which a nut is firmly secured. The screw works up and down in this 

 nut, and to its lower end is attached the folhaer, or moving piece which 

 presses on the substance operated upon. The connection between the 

 screw and this piece is such that the follower rises and falls, but does 

 not turn round with the point of the screw ; and the steady motion of 

 the follower is provided for by making it fit closely to the side-pieces 

 or cheeks of the press, which therefore act as guides. At the lower 

 end of the screw there is usually a massive globular head, pierced with 

 two holes at right-angles with each other, which receive the end of 

 long iron lever, by which the screw is turned. The best screw-presses 

 are made of iron. 



The great space required for turning a long lever is a serious incon- 

 venience in some cases, and has led to the contrivance of several 

 methods for turning the screw with great power by a more compact 

 apparatus. In a press invented and patented by Mr. Dunn, the screw 

 is turned by means of a short bent lever acting upon a ratchet-wheel 

 fixed on the lower part of the screw. In another ingenious modification 

 of the common screw-press, invented by Mr. Pouche'e, a large cogged- 

 wheel is fixed horizontally on the screw, just below the common head 

 for receiving the end of the lever. A small pinion, having a square 

 axis to receive a lever handle, is fixed on the plat ten or follower of the 

 press, and works into the large cogged-wheel. This press is worked in 

 the ordinary way until the screw is turned as far as the lever will con- 

 veniently move it. The bar is then removed, and the handle of the 

 pinion put on, and by turning it the screw may be further depressed. 

 In one form of screw-press for hot-pressing, the plates do not, as in 

 those of the usual construction, need to be removed for heating; 

 they being kept at the necessary temperature by hot air introduced 

 into four hollow columns, which serve the purpose of cheeks to the 

 prat 



While the diminution of the size of the thread affords the means of 

 increasing the power of a screw-press, it is attended by the serious 

 disadvantage of diminishing its strength. This difficulty may be 

 avoided by the use of a double or differential screw. The press may 

 be made of the usual form, excepting that the lower end of the screw 

 is cut with a finer thread than the upper part. This smaller screw is; 

 received into a nut resting on the follower, and capable of turning on 

 it. The head for receiving the lever by which the screw is turned is 

 in this case placed above the head or top beam of the press. When iit 

 use the nut is keyed fast to the screw, so that it turns with it; and 

 the action is exactly the same as that of the common press. When 

 the screw has been turned as far as it will go in this way, the key that 

 I connected the nut with the screw is removed, and the nut is keyed 

 fast to the presser. The screw being again turned, the lower thread 

 enters the nut, so that the presser is depressed only through a space 

 equal to the difference between the width of the upper and lower 

 threads of the screw. By making the two parts of the screw very 

 nearly alike in fineness, the distance traversed by the platten may be 

 diminished, and the pressure increased almost to infinity. 



Screw-presses are occasionally made with more than one screw. In 

 one arrangement of this kind the screws are stationary ; and the nuts, 

 which are fitted into the follower, are turned by means of cogged 

 wheels driven by an endless screw laid horizontally on one side of the 

 follower, and terminating at each end in a winch-handle. Mr. Brindley's 

 press has several screws instead of one, each having a cogged wheel 

 working into another fixed on a plain central shaft, which is moved by 

 a winch and bevil gear. 



SCREW PROPELLER. [PBOPELLKH.] 



SCRIBES. In the article MOSES, in BIOG. Div., this word has 

 been used as a translation of the Hebrew word D^"1tO"iU7, which in 

 the authorised version is translated " officers." The word which is 

 translated " scribe " in the English Bible is "ISO, or in the Chaldee 

 1DD, meaning " a writer." It was applied to an officer of the king, or, 

 as we should say, a "secretary of state" (2 Sam. viii. 17; xx. 25; 

 2 Kings xxii. 3) ; also to a " secretary-at-war," who had the enrolment 

 of the soldiers \uider his care. (Jerem. lii. 25.) It was also used to 

 signify men learned in the Jewish Scriptures. (Ezra vii. G, 11.) The 

 last was the meaning which the word came to have in the later ages of 

 the Jewish state, or rather, as the Jews regarded all learning as con- 

 tamed in a knowledge of their sacred books, the word scribe was used 

 to designate all men of learning. In this sense we find it in the 

 Apocrypha and the New Testament, as the translation of the words 

 i/s, yo/xmij, rojuoZiScurxoAos, for the lawyers (as our version 



