191 (#253) ############################################ PRINCIPLES IN WORSTED DRAWING It should here be noted that while for open drawing a maximum amount of twist may be necessary--although from the point of view of rollers, power consumed, etc., a minimum amount would obviously be desirable-in the case of cone drawing the only twist absolutely necessary is that to ensure the sliver being satisfactorily drawn off the bobbin when being fed in to the succeeding box, although frequently more twist than this will give better drafting fibre-contact. Thus twist will be a function of fibre friction on fibre ; bobbin friction on bearings (type of creel) ; thickness of sliver ; speed of draw-off of sliver ; maximum and minimum diameters of bobbin. These points being decided experimentally would no doubt lead to a method or rule superior to the present almost pure empiricism. Selection of Sets of Gill- and Drawing-boxes. The first principles involved in the selection of gill-boxes as against drawing-boxes or in designing suitable com- binations of gill-boxes and drawing-boxes will be best considered when dealing with drawing and spinning for the coloured trade. It should here be noted, how- ever, that if several qualities of white (undyed) tops are to be mixed together-and this is the best method employed in Yorkshire to maintain a standard quality year in and year out--then perfect mixing is just as important as in mixing black and white tops : imperfect mixing will eventually result in defective streaky pieces. That the streakiness does not appear until the pieces are piece-dyed does not exonerate the spinner from responsibility in causing the defect. 191
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