zontal plate which carries the quadrant pieces and the arbor, and a movement of the "roll cone," Fig. 172. The latter completes the rolling movement imparted to the blank, and is the fundamental idea embodied in the machine. It coerces the movement of the upper end of the arbor, and so imparts a rolling motion to the wheel blank. For each bevel wheel there is a separate cone,-exact, or approximate, twenty-two being supplied. Each forms a portion of a conic frustum corresponding with the cone angle of a bevel wheel, and each has its angle marked upon it. The cones are coerced by steel bands attached to roll boxes on opposite sides of the machine,

H

Fig. 176.-Diagram of Link Motion.

seen in Plate IX., and in Fig. 172. The machine is set by a pointer, and zero line for right and left hand cutting on opposite sides of the teeth. Dividing apparatus is fitted, being either index plates or change gears as desired. All the flanks on one side are cut, and then all those on the other.

There are many details relating to feeds, and opera

tions, which we cannot give space to describe, contenting ourselves with the essential elements, and leaving the photos to explain themselves.

The Robey-Smith bevel gear. generatorplaner, Fig. 174, Plate IX., has two tool arms adjustable for angle, and these operate simultaneously on opposite sides of a tooth, and lift also on the return stroke. Necessarily the angle varies constantly between each cut. Hence the mechanism is so arranged that after each cutting stroke the blank is revolved through a distance equal to the pitch, so that at any given angle each tooth receives a single cut on each flank, after which the angle is changed auto

matically. The generating mechanism employed comprises a series of links as follows:

In Fig. 175, showing the machine in elevation and plan, the cutting tools are seen at A, A carried in their tool boxes, and having their reciprocating arms coerced by the slide B, the details of which are shown in the crosssection. The slides are hinged at the centre a, hence the tool always moves radially towards that centre. The tool boxes receive their motion from the connecting rods c, c pivoted on the crosshead D, and actuated by the adjustable crank E. The slides B, B are extended, and terminate in quadrants F, F. To these are bolted two pieces which terminate in pins G G entering blocks fitted into two slides H H. These last are connected by a series of links which form a parallel motion, as shown separately by Fig. 176. The three points, K, L, M are fixed on the centre line of the machine, and if therefore the lever R, L, T is moved, the two slides H H must move also, approaching to or receding from the centre line by the same amount, and parallel. As their distance apart increases, they open the slides B B, thus increasing the distance between the cutting edges of the tools. The mechanism by which this is accomplished automatically is as follows:

An extension of the lever R, L, T receives a pin s terminating a connecting rod T. The farther end of T can be locked in a slotted link u, which swings round a centre b, and the link is keyed to one of a pair of bevel wheels, one of which actuates the quadrant v. The teeth of the latter engage with teeth cut on a quadrant bar w, and the latter is locked to the carriage which receives the arbor and blank, and the dividing head.

The carriage pivots round the centre c, and is actuated by a worm, engaging in a curved rack. It follows that the motion of the carriage imparts a rocking motion to the lever R, L, T pushing the slides H H apart and increasing the distance between the edges of the tools. The blank thus moves laterally towards the tools simultaneously with the widening of the distance between them. The object of the slotted arm U, is to permit of sliding the connecting rod T to different positions, to suit differences in length of radius of involute tooth curves.

In Fig. 175 a plan of the machine framing in section, is shown with the carriage removed.

The machine of M. Monneret, Fig. 177, Plate X., and Fig. 178, made by H. Ernault, of Paris, is unique in its method of operation, inasmuch as it pitches without a division plate, and also cuts a tooth slightly helicoidal in form. The blank is being constantly rotated, so that only one cut is taken on each tooth at a time, the next being taken on the tooth adjacent, and so on. The helicoidal form is produced by imparting a slow intermittent rolling feed independently of the main movement of rotation, which is continuous. The

A, and the apex of the pitch cone. B is the arbor, and c a quadrant rack, with graduations into degrees, and driven by bevel wheels and a crank, so that one turn of the crank equals one degree, and fractional parts are obtained by other graduations. The headstock cones D, back geared, both actuate the arbor and blank, and tool holder. The first named is effected through change gears E, through a vertical shaft the axis of which lies in that of the pivot a. Hence the motion of the tool slide and that of the wheel blank synchronise by reason of their connection through gears. Detail drawings would be necessary to trace out these connec

movements are wholly automatic during the cutting of one of the sides of all the teeth. The section of the cutting tool is that of the tooth of a crown wheel, and of a semicircular shape when looked at from the face. The blank is carried with its arbor horizontally on a carriage which moves round a pivot, with its axis vertical, and is carried on a horizontal bed, on which it is clamped to impart the sectional angle. But the lateral or flank angles are produced by the movements of the headstock, which impart feed to a tool slide seen in front of the headstock.

In Fig. 178 a is the pivot of the carriage

tions, for which our space is insufficient. But they are briefly as follows:

The change gears E rotate a shaft that passes horizontally below the headstock, driving through bevel gears the vertical spindle concentric with the central pivot a. Thence bevel gears actuate a short horizontal sleeve enclosing a spindle with two sets of wheels, one of which drives a horizontal shaft in the same vertical plane as the gear F. Another spindle parallel with this, and beneath gear G, is driven from the other in a rather roundabout fashion. The motion of the spindle beneath F is communicated to the worm shaft H, which in turn operates the blank

arbor B, through worm gear J. This worm gear is made to fulfil the double function of rotating the blank, and imparting the feed. The worm slides in a key groove in its shaft н, being confined in a box fitted to the screw K. It is therefore fed lengthwise by the rotation of the screw, so fulfilling the function of a rack to the worm wheel as well as its own proper work of rotating the wheel. This feed movement is transmitted from the arbor B, that carries the blank and the worm wheel J, through equal spur wheels to a slotted crank disc м, that in turn actuates a ratchet wheel N with a pawl acting either way. Thence the feed movement is transmitted through the mitre wheels o, to the screw K, which imparts the longitudinal movement to the worm. Thus the helicoidal cutting is done, and the pitching of the teeth.

As already remarked the movement of the tool slide on the front of the headstock synchronises with that of the blank. A slotted disc crank at the front of the headstock spindle, and having an adjustable block and screw, drives the tool box through a connecting rod, and it has also a swivelling movement.

On the spindle of the ratchet wheel N, there is a gear G, which transmits motion through a train of spur wheels to the spindle already mentioned, as lying beneath it, thence through mitre gears to a spindle passing down through the centre of the pivot a. This rotates a horizontal screw working in a pivoted nut below the carriage c, so that whatever the angular position of the latter the screw is parallel with the feed screw K, and this operates the slide p, at a rate that is governed by the angle at which the screw lies, and which in turn is produced automatically by the setting of the carriage. The slide P has a rack on its lower face which imparts motion through a train of spur gears to the tool plate Q through a vertical rack R, engaging with a wheel s, at the rear of the plate. In this way the oscillatory feed is imparted to the tool slide, being one of intermittent rotation about its own axis, and taking place at the termination of each revolution of the blank, which corresponds with a single cut taken off each tooth. A cord b, lifts the tool on the return stroke.

We now come to a small group of generating machines in which rotary cutters are employed. But the same principle underlies their action as that of the reciprocating or planer cutters. That is, they represent the crown or rack tool, and the rolling of the blank past them produces the single curve teeth correctly in all sizes of wheels of the same pitch. There are two good machines in this group, the Warren and the Beale. They each have individualities which render them unique.

is a

The Warren machine, Fig. 179, Plate X., result of the endeavour to produce bevel wheels for chainless cycles. It employs rotary cutters, the cutting face of each of which is identical in angle with the crown gear tooth already noted. Two cutters are used to operate on the opposite sides of adjacent teeth, or those which face each other. They act with reciprocating strokes, while the gear blank and the cutters are rolled past each other. They are rotated in slides which are fed along at the required bevel. A loose connection is required to permit of the double motion, and this is effected through telescopic shafts with gimbal joints, driving equal gears on the spindles. The cutters are fed along the teeth by slides, and rotated at the same time, while the gear blank is oscillated through a distance equal to the length of the arc of contact of the teeth.

A

A recent generator, the Beale, Fig. 180, Plate X., embodies rotary cutters producing opposed faces of adjacent teeth simultaneously. roughing cut is taken in the forward motion of the gear, and a finishing cut on its return, the tooth spaces being roughed out previously. The cutters are carried in slides with angular adjustments, telescopic shafts, and gimbal joints.

The cutters represent the tooth of a crown gear, and the teeth are staggered and interlocked in order to act simultaneously. The inclination of the cutter arbors can be altered to suit gears of different obliquities. Their axes are inclined slightly in a position perpendicular to the tooth angle, in order to impart the flank bevel to the teeth, and this angle is adjustable to suit wheels of different cone angles. They can also be adjusted lengthwise to suit different pitches, though this is rather limited due to the interlocking of the teeth, the operation of which