238 (#310) ############################################ WOOLLEN AND WORSTED SPINNING To ascertain roving required from which to spin any given count of yarn, having given the draft 18.3 Count on Yarn = Dram Roving (40 yd.) Draft decided on Example : A draft of 8 is to be given in spinning a 48's count of cross-bred yarn. What roving should be made from which to spin ? 18.3 18:3 48 = 3:05 dram roving. 6 * } (6 The roving twist will have been decided by the rule already given, and as in both frame and worsted mule spinning there is no drafting-twist other than that already in the roving, it will now only be necessary to decide the "angle of twist” required in the yarn and to insert the turns per inch necessary to give this required angle (as shown in Chapter XII, p. 292). It should be remembered, however, that following a line of research conducted by Mr. Foster Pickles and Mr. Hartley at the University of Leeds, the twist- angle for the greatest strength is that of 22° to 25° given by the rule- D Cotangent of Twist Angle, or D TC X Cot. of Twist Angle T, when reciprocal diameter, ratio of circumference to diameter; and = turns per inch. ' bad spin " it may be necessary to twist up to TE X T D = TT T 1 In a 238
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