Fig. 103.
(178) In grinding the cylinder the cover above the doffer is removed, and the wire surface bared. The cylinder is then stripped in a way which will be afterwards described, and the roller is fixed in brackets R, Fig. [44], placed to receive it. The construction of these brackets is a matter of importance. They are accurately planed, and fitted so as to move to and from the cylinder centre in radial lines. They must be so fixed to the bend or framing that they are quite level and parallel with the surface of the cylinder or doffer, as otherwise they would grind more off the wire at one side than the other. This is an essential feature, and it is also required that they should be set so as to grind lightly, otherwise there is a danger of producing hooked teeth, which are very detrimental to good work. Generally, the remarks just made apply also to the grinding of the doffer, which is effected by means of the brackets S, the doffer cover being removed, and the doffer stripped.
(179) The grinding of the flats in revolving flat engines is usually performed by a roller sustained by the brackets T, which are fitted on the side nearest the cylinder, with a surface against which the flat end is pressed by the weighted levers shown. The accurate grinding of the flats involves a nice problem which is worth a special explanation. As was stated in the last chapter, paragraph 117, the flats are formed with a heel which throws up the edge nearest the licker-in, and thus prevents any rolling up of the fibre. In Fig. [104] a diagrammatic representation of the relative position of the flat end and wire surface is given. The flat end is shown by the letters A B C D, and the wire by C D E F. It will be noticed that the line E F is not parallel with A B, which represents the surfaces on the top of the flat ends, but is parallel with C D, which represents the surface on which the flat travels. It is obvious that if during grinding the flat is held against a prepared surface, by means of its face A B, and traversed thereon, there will be a corresponding formation of the face E F of the wire, which would become parallel with A B. If this happened, the whole object of reducing one of the faces on the surface C D would be destroyed, as while the heel would be in that surface it would be removed from the wire face. But if, on the other hand, the flat is sustained on the face C D during its passage under the grinding roller, the parallel relation of C D and E F is not altered, and therefore the flat is as fit for its work as before grinding. How to sustain the flat when being ground so as to maintain this parallel position is the problem, which is, however, in a fair way towards solution. The steady, forward movement of the flats during grinding somewhat increases the difficulty, but as it is one of the necessary elements of the case it must be duly taken into account.
Fig. 104.
Fig. 105.J.N.
(180) In Fig. [105] an illustration is given of an arrangement patented by Messrs. Knowles and Tatham. The grinding bracket carries a pivot on which the weighted lever F oscillates. The unweighted end of F presses against the top side of the flats as they are successively brought within the sphere of its influence, being of course turned upside down at this point. A plate B is fixed in the position indicated, being of sufficient width to engage with the flat end without touching the wire. B is, as shown, formed with a shoulder, the difference in the height of the two planed surfaces, D and E, thus obtained being equal to the heel of the flat. The grinding roller is indicated by the dotted line, as is also the bearing. The position of the shoulder on B is such that the whole of the wire has been ground before the flat end passes over the shoulder, and the flat is thus kept approximately in correct position for maintaining the parallel relation of the wire and working faces. Before the wire on the succeeding flat begins to be ground, one of the ridges on it passes on to the lower surface E, so that the wire face is brought into a horizontal position.
