(181) In Fig. 106 an arrangement made by Messrs. John Hetherington and Sons is illustrated. The ordinary grinding bracket is replaced by another one, fixed in the same position, which carries at its upper end a slide =K=. This moves in a bed prepared for it in the bracket, and has the necessary bearings formed for the roller =M=. Attached to the slide =K= and the bracket is a spiral spring =T=, which always tends to draw =K= against a stop. The vertical lever =L= extends upward, and its upper end presses against the inner side of the horn of the slide =K=, so that when =L= is oscillated the slide is moved forward. On the same spindle, forming a centre for =L=, a lever =Q= is fixed, which has a vertical tail-piece =P=. A rib is formed on =L= through which a screw is threaded, the point of which presses against the edge of the tail =P=, and is, when adjusted, locked by means of a nut. The flats pass beneath a plane surface fixed to the inside of the grinding bracket, and their working faces are pressed against it by means of the weighted lever =P=. The line of the flat traverse while so pressed is shown by the dotted line =U V=. When a flat enters upon the surface on the bracket it is pressed upwards, as described, and, while so held, the grinding bracket is moved forward over the teeth by the action of the cam =R= fixed on the chain roller shaft. The rotation of =R= depresses the lever =Q=, and gives the required movement to the lever =L= and to the slide =K=. It will be noticed that the slide =K= is placed at such an angle that it traverses to meet the flat, the object of this being to establish such a line of motion of the grinding roller as corresponds to the inclination of the flat relatively to the cylinder during work. The roller traverses in the opposite direction to that in which the flat moves for a certain distance, when it returns and again passes over the wire surface as that is moving forward. During the reverse movement it moves vertically to the same extent as previously made, so that in both cases it grinds the wire points in the desired plane, and thus maintains the true relative distance of both sets of teeth. By the time the reverse movement has taken place, the flat being ground has moved forward sufficiently to pass beyond the range of the roller, and the latter is then ready to grind the next of the series. In this device the principle of grinding by the movement through an angular plane of the roller axis is the central idea, and there can be no question that this is a very likely method of getting a true result. For it is obvious that if the flats were held stationary, and the roller traversed in an inclined plane, the necessary regularity would be given to the wire surface with great exactitude. A similar result is obtainable by similar means although the flats may be slowly moving, and this is demonstrated by the motion just described, which has been used with great success.