Fig. 106.J.N.
(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.
(182) In Fig. [107] is shown a side elevation of Edge’s grinding apparatus, which is made by Mr. Samuel Brooks. Its essential feature consists of a curved plate B, which is fixed either to the grinding bracket A, or to a fixing attached to it. Over this the flats C traverse, and when they reach the centre the snugs at the back are drawn upon the raised portion B1, which is sufficiently long to permit of each flat being in contact with it the whole of the time it is passing under the grinding roller. A plate D is maintained in a position above the flats, and the method of forming it and regulating its position constitutes one of the chief features of this arrangement. The grinding roller G is sustained by a bracket or bearing, in which its axis F rotates. The bracket rests upon a cylindrical stem E1, fitting inside a cup, and also in a similar recess or barrel E. The latter has a long boss which forms part of, or is attached to, the plate D, and E1 is screwed and fitted with two cylindrical nuts. Thus, by adjusting the nuts, the distance of the centre of F from the under surface of D can be varied at will, and the pressure of the grinding roller upon the wires fixed. The action of this mechanism is as follows: As the flats C traverse they ride upon the projection B1, and their working surfaces are forced against the under side of the plate D. The latter is shaped so that the traverse of the flat causes one side of it to become depressed and the other to be elevated. The peculiarity of this arrangement lies in the fact that the change of position of the plane of the flat faces is sufficient to ensure all the wire points being presented to the action of the grinding roller in their correct plane. In other words, the effect is nearly identical with that obtained when flats are held separately in a stationary frame, and the grinding roller passed over them. Not less important is the ease with which the position of the setting plate D can be adjusted relatively to that of the grinding roller. This power of adjustment is the chief feature of this mechanism, and as, when it is once made it is constantly maintained, each of the series of flats will be so ground that the distance of its wire points from its working face will be identical with that of each of its fellows. Thus a set of thoroughly good flats is obtained, each of which is in the best condition to do its work. A further point which it will, perhaps, be well to mention is, that the power of adjustment, existing by reason of the two nuts shown, permits of the flat ends being subject to the required pressure during grinding, which is afterwards constantly maintained.
Fig. 107.J.N.
Fig. 108.J.N.
(183) Fig. [108] represents in partial section Higginson and Mc.Connell’s patent, which has been adopted by Messrs. Dobson and Barlow. It consists of a bracket A fixed as usual to the machine framing, and having at its upper portion C a slot in which the small slide D is fitted. This slide has its underside shaped to the extent necessary to give the flats the required amount of inclination during grinding, and at the end of this surface is formed with a lip as shown. A spiral spring E is fitted in the slot, and presses against the end of the slide when the latter is in its normal position. The flats G, of which there are only two shown, travel in the direction of the arrow, and when turned face up the chain lugs mount upon the nose of the short lever H. A bell-cranked lever F is fixed on the same shaft as H, its vertical limb having a set screw I fitted, by which its range of movement is limited, while its horizontal arm carries a balance weight. As the flats traverse they alternately mount upon the higher part of H, and are thus pressed into contact with the inclined part of the slide D. Immediately afterwards the flat comes in contact with the lip, which prevents its further forward movement. At this time it is in such a position that the wire surface is horizontal, and while in that position it is passed under the grinding roller B. As it traverses it carries the slide D along with it, gradually compressing the spring E until the wire has been entirely ground. When this has happened the slide makes a little further forward movement—its entire traverse being shown by the two vertical dotted lines—when the chain lugs pass off the nose of H, and the flat falls clear of the slide D. Immediately this occurs the spring E pushes the slide back, and it is ready to receive another flat. The chief feature of this motion is the employment of the sliding wedge. When the flat is pressed on to this it is held as though it was on a stationary bed, and is, by reason of the horizontal position of the slot, maintained in a constant plane. Thus the wire surface is presented to the action of the roller in a plane parallel to that of the slot, so that, whatever the variation in the flat end caused by wear, it is not affected. There is another point which is somewhat important. The tension upon the chain links caused by the friction of the flats upon the bend is very considerable, and results in a gradual lengthening of the pitch of the chain. If, in addition to this, the extra friction set up by the pressure of the lever H on the flat, thus causing the latter to be forced against the surface of a plate, be taken into account, this tendency to lengthen will be increased. The extent to which this is to be considered varies naturally with the pressure exerted. Although it is not perhaps great it is appreciable, and it is a matter to be considered. In Higginson and Mc.Connell’s motion this friction is slight, as the slide D is arranged to move without much power, although the compression of the spring towards the end increases the amount required. As the wedge springs back into position it has to slide over the face of the next of the series of flats, which by this time has passed upon the end of the lever H. Thus, although the flat travels forward without friction, there is a certain amount to be considered as the wedge is passing into position on each flat, the pressure being then exerted as in the case of a fixed plate until the flat presses against the lip, and the wedge begins again to slide.
Fig. 109.J.N.