DIVIDING ENGINE, or th:I.ING ENGINE. A machine devised to rule tine lines at regular intervals by means of a diamond point or other sharp edge. The most common use of such ma chines is for the purpose of dividing the cir cumference of a circle into degrees and minutes or other divisions as is necessary in the construc tion of surveying and astronomical instruments. micrometer screws, spectrometers, and other physical instruments, as well as in many com mercial machine,: and also for the purpose of dividing a length into aliquot lulls as in the making of meter rods and similar instruments. Another use to which they are put is that of the preparation of diffraction gratings (q.v.), in which it is necessary to have the means of ruling a great number of lines, exactly parallel and at exactly equal small intervals apart. thratings are made with as many as 100,000 lines in a distance of live or six inches.
The first instrument for the ruling of gratings was made by Joseph von Fraunhofer (9.v.) ; others have been made by Nutherfu•d, Rowland, and but all are based on the same general principle. The machine consists of a cylinder on which a s•rew-thread is cut and which carries a large nut, the two together being like an ordinary bolt and nut. The ends of the screw are held in yokes, so that it can turn on its axis, and the nut is held on 'ways' parallel to the screw. Thus, as the screw is turned by a crank or otherwise, the nut advances or re cedes. A cutting edge is set at some point above the screw, in such a manner that it can he made to make a line at right angles to the axis of the screw. The piece of glass or metal on whose surface the rulings are to be made is attached to the nut, and the operation is as follows: A line is made by the cutting edge; the screw is turned through a certain fraction of a complete revolution—e.g. one-thousandth—thus carrying the not and the surface forward a small distance; a second line is ruled; the screw is again turned through the same angle as before; a third line is ruled, etc. Thus, if the pitch of the screw is 20—i.e. if there are 20 threads or spirals on the screw in each inch along its length—there will lie 20.000 lines per inch ruled on the sur face. The nut is split in two. the halves being
hinged at the top and having below two pro jections or 'wings.' When the machine is to be used, these are clamped together. At the end of the ruling the wings are opened. and the nut, hieing thus released from the screw, can he pushed back to the starting-point.
It is evident that the machines must he rigid, the 'ways' exact, the screw of perfectly uniform pitch, the of the screw regular, the cutting of the line exactly straight. All modern machines are automatic; a large toothed wheel is attached to the screw at one end. and this turned by level.•. one tooth at a time; the cutting edge is a diamond point which is al lowed to drop on the ruled surface, is drawn across, then lifted. pushed hack to the original position. vie. There are always periodic er rors in the use of any dividing engine. oc casioned by irregularities in the toothed wheel, the end of the screw butts against some fixed support. and el-ewhere. These may he counteracted by a (let ice due to Rowland lvhmcii 41t prod- upnu the act it•II of a lever resting on a cam attached to the axis of the screw. The end of 11.e l•t•r fastened to a rod Ithich is parallel to the screw. and to which is at ladled, by means of a short crank, a frame work supported under the screw and free to grove horizontally. Part of this framework consists of two steel rods parallel to the screw, between which the two 'wings' of the nut can just move freely, a- the nut is carried forward by the screw. Thus. if the cam raises its lever. the rod will turn, moving the framework holding the wings of the nut. and thus giving the nut a slight turn independent of the action of the screw. It is a matter. therefore. of trial to find a cam of such o and to place it on the axis of the screw in such a position, that by its motion the irregular motion of the nut due to the irregu la•ities of the machine may be made perfectly regular. Fora description of the construction of a 'perfect' screw. reference should be made to the article by Rowland. in the Entrlclo ytudia Brie', on lea. full description of Row land*, dividing engine is given in The Colleetcd l'a rs of llrnry .1. leowla ad I Baltimore, 1902).