(166) In fastening the clothing upon the flats several methods are pursued. A reference to Fig. [83] shows two of these. In A, which is 2 inches wide, and B, which is 13⁄8 inches wide, the edges of the flats are drilled with small holes, and the strip of clothing is similarly punched. One side of the strip is then fastened to the flat by means of lead rivets, and it is then drawn tight along its whole length by a special clip. The other edge is, while the strip is held in tension, riveted firmly in a similar manner. A machine for this purpose, made by Messrs. Dronsfield Brothers, is shown in Fig. [84]. Another method is one originated by Messrs. Ashworth Brothers, and is shown in C and D. In this case the strip is attached by means of wire stitching, the flat being sawn at its edge at regular intervals, as is very clearly shown. A third plan is illustrated in Figs. [85] and [86] in partial perspective and transverse section, this being made by Messrs. John Whiteley and Sons. A clip is passed through the clothing and flat, and is then clenched, as shown separately in Fig. [87]. The strip of clothing is then drawn tight, and the second clip fixed in the same way. This method is rapid and effective, and possesses one important advantage. By it the margins of the flat strip are protected from being frayed by the revolving brush used to clean them.
(167) In dealing with the construction of the flats it has been shown that there is a movement towards the use of shorter ones, for the reason that it is felt to be desirable to prevent any deflection by having a stiff flat. Upon this point the consideration of the advantages of various systems of fastening the clothing largely turns. It is quite clear that any removal of metal, either by drilling or sawing, is likely to weaken the flat. It is, however, not so readily seen which is the most weakening, but actual experiments show that wire sewing is so. Mr. B. A. Dobson, of Bolton, has made a series of tests of flats, both drilled and sewn, to ascertain the deflection during working and grinding positions, and the side deflection. These establish very clearly the superior strength of the riveted flat, which is very considerable. For instance, a flat 455⁄8 inches long by 13⁄8 inches wide, with the same thickness in flat and web, gave the following deflections when loaded with a 1lb. and 2lbs. weight respectively. Unclothed, sawn for wire sewing: 1st, when face up, 1⁄380th and 1⁄200th inch; 2nd, when on its side, 1⁄330th and 1⁄166th inch; and, 3rd, when face downwards, 1⁄660th and 1⁄400th inch. Unclothed, drilled for rivets, the deflections in the three positions named were as follows: 1st, 1⁄1000th and 1⁄500th inch; 2nd, 1⁄400th and 1⁄275th inch; and, 3rd, 1⁄875th and 1⁄400th inch. The reason for this is not far to seek. The riveted flat has throughout its length an unbroken metallic surface along its edge, while the sewn flat is broken at intervals to permit the passage of the wire. For the reasons given in paragraph 118, the difference between 1⁄660th and 1⁄875th inch is material, especially when the settings of the flats are supposed to be regulated to the 1⁄1000th inch.
(168) In Fig 88 is illustrated a plan by which the necessity for piercing the flat either with holes or nicks is entirely obviated. This is patented by Mr. Tweedale, manager for Messrs. Howard and Bullough, and consists in the employment of a metallic clip, which grips the clothing at one side, and is bent round and under a small rib on the underside of the flat. The clip is closed by means of a special machine, which runs rapidly along the flat, the two sides being gripped simultaneously, and the fillet stretched by the same machine and at the same time. With this construction the maximum strength of the flat is preserved throughout all its positions and under all working pressures. A similar arrangement is used by Messrs. Ashworth Brothers, but the shape and construction of the clip and the method of fixing slightly varies from that described. It is to be noted, however, that the width of the flat strip must be rather less in each case than that of the flat, and that the strip must in consequence be stretched so as to cover the surface. It is essential that the clips shall be fixed so as to be in contact with the planed edge of the flat throughout its entire length. The edges of the flats ought to be quite straight, especially if they are closely pitched, as otherwise they would come into contact in places. If, therefore, the clips referred to are not pressed closely against the sides of the flats throughout their entire length the danger of touching is increased.
Fig. 84.
Fig. 85.
Fig. 86.