Fig. 2080.
Referring to the dividing mechanism, e, [Fig. 2077], is an index-wheel operated by a worm. e1 is an arm with a locking tongue. Motion from e is conveyed to the shaft g through a swing-frame, shown in dotted lines in [Fig. 2077], and a train of gears g2, g3, g4, g5, g6. On shaft g, [Fig. 2078], is a pair of angular-toothed beveled pinions, h1 h2, and on shaft h, [Fig. 2080], is a pinion h3, driving a pinion h4, which in turn drives pinions i i1. The latter drive the worm h′ which operates the wheel h. The two shafts carrying i i1 are supported by a piece f, the arm of which appears in section. This is fixed on the large toothed wheel g, indicated by the dotted lines in the same figure. The piece f above referred to is not fully shown in the engraving, portions of it having been omitted in order to show the mechanism previously mentioned. The wheel h is mounted on shaft d′′, and is used to revolve the face plate d′, all as shown in [Fig. 2078]. The wheels g2 g3 are change wheels, whose relative diameters determine the number of turns the wheel e must make for a given pitch. The arm e1, [Fig. 2077], is provided with a spring to hold the index pin into the notch of the index wheel. From this description it is obvious that when the number of the teeth of the wheel to be cut is a multiple of that of the wheel h, the number of turns to be given to the tangent screw h′, [Fig. 2080], is exactly determined by the ratio existing between these two numbers. On the other hand, where the number of teeth required is not a multiple of the teeth in the wheel h, the number of turns to be given to the screw will be equal to n plus a fraction. In the first case, if all the intermediate gears between the dividing apparatus and the tangent screw are arranged to transmit to the former a number of definite turns, it will suffice to make the crank describe the number of turns indicated by the ratio the wheel e bears to the worm-wheel. In the second case, in order to give the tangent screw n turns plus a fraction by giving the crank n + turns, it is necessary to employ several wheels, for which the ratio must be calculated. If the division so obtained is not an exact divisor of the number of teeth of the wheel h, it is necessary that one of the wheels forming the combination shall have a number of teeth which is a multiple of the division mentioned.
Another consideration with reference to the number of turns to be given to the crank of the dividing apparatus is mentioned in the inventor’s description of this machine. The smaller the number the greater will be the chance of error in the result; for example, if it be supposed that a division corresponding to one turn of the tangent screw is to be made, if only one turn of the crank is made, the play unavoidable where easy movement is secured will be repeated and multiplied in the same way that an error is produced after a certain number of divisions. If, on the contrary, the mechanism be arranged so that the number of turns of the crank is multiplied in obtaining one turn of the tangent screw, the error will be appreciably reduced. It is therefore recommended by the designer of this machine to arrange the train of gears so as to give a certain number of full turns to the crank in all cases. If, after having cut the teeth in the blank, it is desirable to go over them again, it is simply necessary to turn the screw j which engages with the gear-wheel j1.
Fig. 2081.
The next feature to be described is the adjustment of the cutter. In some cases it is necessary to incline the cutter in such a way that the axis of the shaft carrying it forms a certain angle with the vertical. This is the case in cutting angle teeth, as shown in [Fig. 2076]. In order to produce the necessary angle for such teeth, it is only necessary to turn the worm k that engages with the worm-wheel k1, [Fig. 2077]. This wheel is fast on to the piece m, and the latter, when set to the desired inclination, is kept in place by means of bolts o, [Figs. 2077] and [2081]. In some cases it is necessary to incline the cutter in such a way that the axis of the shaft that carries it does not cease to be in a vertical plane perpendicular to the shaft d, this being the case as illustrated in [Fig. 2082]. In order to obtain this obliquity the small shaft m is turned, and the movement so obtained is transmitted by means of two small pinions m2 m3 to the shaft carrying at its extremity the screw n′. This screw gears with the segment n′′. The latter is fixed to a piece j, furnished with bearings for the reception of the shaft that drives the cutter spindle, which is adjusted endways by means of the nuts shown.