A tuck stitch is composed of a held loop, one or more tuck loops and knitted loops (Fig. 9.4). It is produced when a needle holding its loop (T) also receives the new loop, which becomes a tuck loop because it is not intermeshed through the old loop but is tucked in behind it on the reverse side of the stitch (Fig. 9.5). Its side limbs are therefore not restricted at their feet by the head of an old loop, so they can open outwards towards the two adjoining needle loops formed in the same course. The tuck loop thus assumes an inverted V or U-shaped configuration. The yarn passes from the sinker loops to the head that is intermeshed with the new loop of a course above it, so that the head of the tuck is on the reverse of the stitch.
The side limbs of tuck loops thus tend to show through onto the face between adjacent wales as they pass in front of sinker loops. Tuck stitch structures show a faint diagonal line effect on their surface.
In analysis, a tuck stitch is identified by the fact that its head is released as a hump shape immediately the needle loop above it is withdrawn. A knitted loop would be required to be separately withdrawn and a miss stitch would always be floating freely on the technical back.
Fig. 9.5 Technical face of tuck stitch fabric.
Fig. 9.5 Technical face of tuck stitch fabric.
The tuck loop configuration can be produced by two different knitting sequences:
By commencing knitting on a previously empty needle (Fig. 9.6). As the needle was previously empty, there will be no loop in the wale to restrict the feet of the first loop to be knitted and, in fact, even the second loop tends to be wider than normal. The effect is clearly visible in the starting course of a welt. By introducing rib needles on a selective basis, an open-work pattern may be produced on a plain knit base.
By holding the old loop and then accumulating one or more new loops in the needle hook. Each new loop becomes a tuck loop as it and the held loop are knocked-over together at a later knitting cycle and a new loop is intermeshed
with them. This is the standard method of producing a tuck stitch in weft knitting (Fig. 9.4).
Successive tucks on the same needle are placed on top of each other at the back of the head of the held loop and each, in turn, assumes a straighter and more horizontal appearance and theoretically requires less yarn. Under normal conditions, up to four successive tucks can be accumulated before tension causes yarn rupture or needle damage. The limit is affected by machine design, needle hook size, yarn count, elasticity and fabric take-down tension (Fig. 9.7).
Each side of the head of a tuck loop is held by a sinker loop (S) from the course above (Fig. 9.9).When tucking occurs across two or more adjacent needles, the head of the tuck loop will float freely across between these two adjacent sinker loops, after which a sloping side limb will occur.
Dependent upon structural fineness, tucking over six adjacent needles is usually the maximum unit before snagging becomes a problem. (NB: Tucking across no more than two adjacent needles is generally the limit because the tuck is not secured at the middle wales when tucking across three or more needles.) For a greater number of adjacent needles, the accordion sequence (Section 10.4.3) where occasional tucks tie-in a floating thread, is preferred.
A tuck loop is notated either as a dot placed in a square or as a semi-circle over a point. A held loop is assumed to extend from the course below, up to the course where the next knitted loop is notated in that wale, as this is where it intermeshes. Selective 'tucking in the hook (Fig. 9.10) is achieved on latch needle weft knit-
ting machines by lifting the needle only half-way towards clearing height to tuck height. The old loop opens the latch but remains on the latch spoon and does not slide off onto the needle stem. It remains as a held loop in the needle hook where it is joined by the new loop, which becomes a tuck loop when the needle descends to knock-over.
The latch needle, because of its loop-controlled knitting action, is capable of being lifted to one of three stitch positions to produce either a miss, a tuck or a knit stitch; this is termed the three step or three way technique (Fig. 9.11).
On V-bed flat machines, raising cams, split into tuck and clearing height cams, are known as cardigan cams. They are not available on older machines so only collective 'tucking on the latch on all needles in one bed can be achieved. The stitch cam is raised so that the needles do not descend low enough to cast-off the held loops from the closed latches (Fig. 9.12). This is not a preferred technique because there
is no individual selection and there is the danger of the held loop slipping off and producing an intermeshed loop with the tuck, converting it into a knitted stitch.
The first tuck presser bearded needle frame was invented in Dublin in 1745. A bearded needle tucks when its beard is miss-pressed so that the old loop is not cast-off and remains as a held loop, inside the beard, with the newly-fed tuck loop.
Tucking for inlay may be achieved by deflecting certain needles during inlay feeding so that the yarn passes across the beards of the selected needles, forming a tuck instead of floating across their backs. Selective tucking requires cut-away pressing edges or individually controlled presser bits.
Tucking may occur accidentally as a result of stiff latches, imperfect pressing, imperfect knocking-over of old loops, or thick places in yarn.
Tuck loops reduce fabric length and length-wise elasticity because the higher yarn tension on the tuck and held loops causes them to rob yarn from adjacent knitted loops, making them smaller and providing greater stability and shape retention. Fabric width is increased because tuck loops pull the held loops downwards, causing them to spread outwards and make extra yarn available for width-wise extensibility. Fabric distortion and three-dimensional relief is caused by tuck stitch accumulation, displacement of wales, and by varying numbers of tuck and knitted stitches per wale.
Tuck stitches are employed in accordion fabrics to tie-in the long floats produced on the back of single-jersey knit/miss jacquard, thus reducing the problems of snagging that occur with filament yarns.The tuck stitch may also be employed to produce open-work effects, improve the surface texture, enable stitch-shaping, reinforce, join double-faced fabrics, improve ladder-resistance and produce mock fashion marks.
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