Lapping diagrams are drawn around horizontal rows of points that represent needles in plan view, usually assuming the pattern mechanism to be on the right. As the guides position themselves in the spaces between needles, the positions between the vertical columns of points can be given chain link numbers commencing with the '0' position, which is to the right of the right-hand column of points.
Provided the direction and extent of the overlaps are correctly indicated in the lapping diagram and chain notation, the underlaps will always be correctly positioned as each extends from the end of one overlap to the start of the next.
Figure 23.4A represents a diagrammatic plan view of a two-course repeat sequence. S1 and S2 represent the swinging motions and O and U represent the overlap and underlap shogs at each course.
In the lapping diagram (Fig. 23.4C), the first overlap will be drawn in a curve over a point from space '1' to space '0' and the second from space '2' to space '3'. The lapping diagram is completed by joining the overlaps to each other with underlaps and the chain is notated as 1-0/2-3/ where-represents an overlap and / an underlap.
The shogging movements are produced by the transition from one link to the next, whereas the swinging motions occur whilst the push-rod roller of the guide bar is in the centre, so that no shog is produced.
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