The angle of twill weave is determined by the amount of shift in the points of interlacing.A one pick one end shift twill weaveis called 45 degree twill.A twill weave which has more than one pick shift and one end shift is called steep twill; if the shift is more than one end and one pick it is called reclining twill.
Factors affecting angles of twill weave
The angle of a twill is affected: (1) by the manner in which the ends and picks interlace;
(2) by the relative number of ends and picks per inch.
Fig. 11 illustrates the method of running up twill lines on design paper so as to form different angles.In the first twill line at the bottom, the twill moves four squares filling way, or across the design, and then one square up; by this means an angle of 14° is formed. In the next case the twill moves three squares filling way and then one square warp way, forming an angle of 18°. In the next case the twill moves two squares Filling way and then one warp way, which gives an angle of 27°. By carefully noting each twill line, the method of forming different angles will be readily understood. Twills are spoken of as being such a degree twill, the 45° twill being the most common, as it is the angle formed by all regular twills. A twill that forms a certain angle on regular 8 X 8 design paper will not form Fun · that same angle in the cloth unless the number of ends and picks per inch and the counts of the warp and filling yarns are the same. For example, the 45° twill shown in Fig. 12 is shown on 8 X 8 design paper; that is, the design paper has eight vertical rows of squares and eight horizontal rows in the same distance, warp or Filling way. Since a row of squares across the paper represents a pick and a row of squares vertically represents a warp end, a twill or any design on this kind of design paper shows the weave as it would appear in the cloth if the same number of picks per inch as ends per inch is inserted.Suppose that twice as many picks are placed in 1 inch of the cloth as there mmm are ends per inch; then in order to give a correct representation of this on design paper, a paper should be used that contains twice as many horizontal rows of squares in a given space as it has vertical rows of squares. Fig. 13 shows the twill in Fig. 12 on design paper of this kind; it will be noticed that an angle of 27° is formed. On the other hand, if there are twice as many ends per inch in the cloth as there are picks, an angle of 63° will be formed with this same twill; Fig. 14 illustrates this point.
Angles of teill weave(Contd...)
It will be noticed that in both Figs. 13 and 14 two repeats of the weave are shown. Ordinarily, however, 8 X 8 ' design paper is used in constructing designs even if the fabric is to be woven with more picks than ends per inch or vice versa. It is only in jacquard designing and for some special fabrics where it is desired to preserve the symmetry of a figure, or pattern, that a design paper is used corresponding to the relative number of ends and picks per inch in the fabric.
When working out twill weaves on design paper it should be understood that whatever kind of twill the weave may be, the marks or blanks for one repeat should not be extended beyond the number of ends and picks that has been decided on.
For instance, if one repeat of the weave occupies 4 ends and 4 picks, the fifth end would be like the first, and so on; also the fifth pick would be like the first pick. and so on. Consequently, to show one repeat only 4 ends and 4 picks are necessary. All regular 45° twills repeat on the same number of picks as ends, so that if the base of such a twill occupies 12 ends, it repeats on 12 ends and 12 picks. Twills that (Q) form an angle of more than 45° are known as upright twills, while those that form an angle of less than 45° are called oblique, or reclining twills. By carefully studying the following regular 45° twills and the explanations previously given, a good understanding of the method of working out the twills may be obtained.
Fig. 15 is a regular 45° twill 5/3 2/3twilled to the right; Fig. 16 is a regular ¤¤¤l 45° twill 4/2 1/2 2/3 twilled to the right; Fig. 17 is a regular 45° twill with the base 1/5 6/4 twilled to the left. Several twills that are constantly used in the construction of the more common fabrics are known by definite names. Among them are the filling- flush prunelle, Fig. .18 (a); the warp (g) prunelle, Fig. 18 (b); the cassimere, Fig. 18 (c); the filling-flush crow, Fig. 18 (d); the warp-flush crow, Fig. 18 (e); the filling-twill, Fig. 18 (f); the warp-Flush Albert twill, Fig. 18 (g); the filling-broken crow, Fig. 19 (oz); the warp-flush broken crow, Fig. 19 (b); the Venelion (I) twill, Fig. 19 (c); and the Mayo, or mam Campbell, twill, Fig. 19 The weaves shown in Fig. 19 are not regular twill weaves but are weaves that are well known. Show two repeats in both ends and picks of a regular 45° twill having the first pick arranged 3/3 1/1.
A steep twill will have twill angles more than 45 degree nd reclining twill will have angles less than 45 degrees.The angle of twill line in fabric depends on the pick and end densities in the fabric.A 45 degree twill woven with the same yarn in warp and filling, but with the ends/inch different from the picks/inch will not have an actual twill angle in the fabric of 45 degree.