The principles governing design areas apply to all wheel selections, including sinker-wheels with plush and plain plating sinkers, provided that their set-out remains unchanged during knitting (Fig. 11.10). The wheels are generally of the same size and gauge on the same machine. The needle producing the starting wale of the design is marked and, as the cylinder turns during the first revolution, it will align with the marked starting trick of each wheel in turn, to ensure that their selections commence above each other in the same wale. As the widths will be of the same size and similarly arranged in each wheel, they will be built-up into a pattern depth, each exactly aligned with the previous one, commencing with the first feeder selection. They will therefore be arranged as columns of pattern widths around the fabric tube.
A rectangular design area is developed if the chosen width (W) is the highest common factor (hcf) of the cylinder needles (wales in the fabric tube) (N) and the tricks in one wheel (T).
A non-spiral design area, showing no fall (f) in courses from one pattern width to the next across the fabric, is produced when T is an exact factor of N, so that W = T. In one machine revolution, the wheels will make an exact number of turns and their starting tricks will re-align with the starting needle in the cylinder, thus completing the pattern depth.
The number of pattern width columns around the fabric tube (P) = N/W. The pattern depth (D) in feeder courses = Feeders (F) x depth per feed or number of pattern widths in one wheel (d).
To convert the number of courses to pattern rows, it is necessary to divide them by the number of colours (C) in the design.
D = F x d = 36 Therefore depth in pattem rows = 36/C = 18.
With a design area of 140 wales by 18 pattern rows, it is too wide and too shallow for most designs.
Spirally-developed designs are used because they provide a greater pattern depth but, as a consequence, they also produce a fall between one pattern area and the next one adjacent to it. They are produced when T is not an exact factor of N (i.e. N = nT + RT) where n = a number of whole turns of the wheel and R is a fraction of a turn.
At the second revolution, the starting tricks in the wheels will not re-align with the starting needle in the cylinder, and the continuous selection of the wheels will have 'shifted' or 'moved on' compared to the cylinder needles. Each wheel can be set-out with more than one width (d > 1) and W will be a factor of R, so that a different width selection will be produced in the first column of design and in all the others in turn at the next machine revolution, as a result of the shift of the wheels.
The pattern depth will therefore be increased by a multiple of d and it will be built up during d revolutions of the machine, after which the starting tricks of the wheels will again re-align with the starting needle in the cylinder because, by then, they, as well as the cylinder, will have completed an exact number of turns.
The disadvantage of spirally-developed designs is that each wheel is producing a number of different pattern width selections in adjacent columns along the same feeder course and, as these are for different courses in the pattern depth, the pattern areas will appear to fall from one column to the next.
The fall (f) is expressed by the difference between the two adjacent widths in courses in the direction of knitting, which is towards the right in fabric produced on machines with clockwise revolving cylinders. It must be understood that each wheel has shifted sideways by the same amount, so that its width selections are placed exactly above those of the first wheel and are in the correct sequence for the depth. Therefore, although the areas show a fall or drop, the courses are always correctly placed within the pattern depths.
Half-drop design areas occur when N = nT + 1/2T so that W = 1/2T and d = 2. It will take two machine revolutions to develop the pattern depth in the starting pattern column but the wheels will, as they turn, place the selection for their second width in the adjacent column and thus produce a half-drop of the pattern area. Using the previous machine data as guide, N = 1400 + -T = 1470; W = hcf of N and T = 70; N/T = 10--; P = 21, D = F x 2 = 72. The wheel of the first feeder will make course width 1 and (F + 1). As the two widths will occur in adjacent columns, the fall will be 36 courses in a total depth of 72 courses.
(Calculations for other types of pattern drops are included in previous editions of this book but are no longer in general use.)
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