116 (#170) ############################################ WOOLLEN AND WORSTED SPINNING 3rd Example : I L = 2.0 turns per i in. ; 5 1 4th Example : I I == I turns per in. L I 3 These last particulars are designed to give one com- plete turn round the thread of the longest fibres. It does not follow that one turn is sufficient or that it may not be too much. For slippery silk it is quite conceivable that three or four turns round the thread may be necessary to hold the sliver together during spindle- drafting ; for a very rough and hairy material less than one turn round might be desirable. There is an inter- esting research based upon the frictional co-efficients of the fibres under test, possibly along with certain other minor factors. If the basis of three turns round the thread be taken, then the formula stands ỉ = drafting turns per in. required (see Fig. 38). . . Having decided upon the angle of drafting-twist, the second point-how to maintain this throughout the spindle-drafting of the slivers—must now be faced. The conditions are- 1. The rim-shaft of the mule is usually putting in twist at a constant rate during the outward run of the carriage ; 2. The sliver is being drafted finer and finer as the carriage recedes and consequently requires twist for the additional length plus more and more twist as the thread becomes finer, to maintain the twist angle decided upon. This 116
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