Spot or knop effects require the use of both a plain presser and a cut presser (Fig. 27.11). The front and back guide bars might be full-threaded and knit a locknit or reverse locknit in co-operation with the plain presser. At various selected points in the production of the fabric, these two bars stop overlapping and the plain presser is withdrawn so that the cut presser operates in conjunction with a partly-threaded middle guide bar to make the knop overlaps.
Adjacent needles hold their ground loops until fabric knitting recommences, when the excess knop loops will be thrown upwards in a relief effect on the technical face. When not knitting, the back bar must evade the middle bar and the middle bar must evade the front bar, otherwise their vertically-floating miss-laps will protrude between the wales on the technical face.
Selective miss-pressing of all needle beards is achieved on modern machines by turning an eccentric disc through 180 degrees inside the circular opening of the presser bar. In one position of the disc, the presser advances sufficiently to close the beards. In the other position, the presser does not advance to contact the beards.
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