Knitting machines are divided into two classes according as they produce fabric in flat portions or in circular shape. In the methods of stitch formation already described the courses of loops are constructed in a flat piece, whilst the circular machine makes its fabric in circular form. This system of fabric production has many advantages over the plain width fabric and is indispensable for various branches of the hosiery trade. In seamless articles such as hose and half-hose it is an advantage to have them worked circular as this fits the shape of the body part where they have to be worn. Also large quantities of fabric are expeditiously worked on the circular frame with big diameter head, these lengths being often suitable for making into articles such as nightdresses where the circle of fabric may be used for the body part. The great bulk of fabrics made on large diameter circulars are intended for the cut-up trade, and they are so made because of the great advantages possessed by such frames in point of speed. In flat rotary frames where the work is made by an alternating motion of the thread-carrier from side to side a principle of motion is utilized which has a certain jerkiness as characteristic. With the circular principle of motion there is an entire absence of jars and jerks in working, the movement being steady and accurate, whilst the addition of eight or more feeds to a machine makes an enormous production possible. One of the most easily understood forms of this type of motion is incorporated in the well-known Griswold type of circular knitting machine used still in considerable numbers in one or other of its modifications for the footwear trade. An illustration of this class of knitting machine is shown in section in Fig. 50, which is so arranged as to give a side view of the cylinder which makes the plain work and the dial as used for rib work. The machine is constructed in a circle which for men's half-hose is about 4¼ in. in diameter for a normal size, and the upright cylinder marked C is fitted with grooves cut according to the set of the article as it is fine or coarse. An average set of machine is 84 needles in the 4¼ in. diameter, but there are as few as 64 in the cylinder for the coarse varieties, and up to 144 for fine gauges of footwear. A section of the dial or ribber, as it is often called, is shown crosswise at D with the cams at CB1. The cylinder needles are indicated by CN whilst the dial or ribber needles are marked DN. The thread-carrier is shown on the right by TC, whilst the thread is recognized by the letter T.

Movement of the Parts.—The upright cylinder receives its rotatory movement by means of a handle at the side which operates the bevel gearing to drive the thread-carrier and the set of cams. The action of the cams is to give the needles their up-and-down motion in loop formation, they move round to work on the needle butts in succession, pushing them up so that the hooks receive the thread from the carrier, and drawing them down again so as to discharge and knock over the loops. The thread-carrier and the cams are made to revolve together by the turning of the machine handle, or in the case of power machines this motion proceeds from the drive of the frame. The machine may be worked without the dial, using the cylinder needles only for knitting, in which case plain stitch fabric is produced as would be required for a plain hose article. When ribbed work is needed the dial or ribber needles are set in connection with the upright cylinder needles and are made to rotate with the cylinder so that the dial needles share the thread with the cylinder needles. The process of feeding the thread to both sets of needles is clearly illustrated at the right-hand corner of Fig. 50, where the thread T is seen to be proceeding through the eye of the thread-carrier TC, when part of the thread is taken by the cross needle issuing from the dial and part taken by the upright needles working in the cylinder. The dial needles discharge their stitches towards the right, whilst the cylinder needles throw their stitches over to the left, and this alternation in direction of the stitch discharge is responsible for the ribbed effect in the fabric. The ribber needles radiate from the centre of the dial outwards, whilst the cylinder needles all stand parallel to each other in an upright circle. The fabric F proceeds down the centre of the machine, as shown, and is maintained at the correct tension by suspension of weights in the hand machine, whilst for the power frame we have an automatic motion for winding up the fabric as it is produced.

Stitch Formation.—The principle of stitch formation may be understood from an examination of Fig. 51, which gives a view of the type of cams found inside the cam box of the hand machine. Except where it is required to knit the needle rests on what may be termed the normal ledge, and it is only moved from this position when the cams reach it to make it knit. The normal ledge is indicated by L and L1, and whilst the needle is resting on this part of the platform no motion can result. To form the stitch the first stage is to have the needle knocked above the general level of the needle hooks to catch its share of the thread as it is being fed into the needles, and this push-up is given by the small triangular-shaped cam marked PC which raises the needles just sufficiently above the normal height to receive their share of the thread from the carrier. This done, the needle is at once operated upon by the knitting cam KC, which is of the shape shown so as to draw down the needle for the discharge of the loop. The butts of the needles N are depressed by the knitting cam KC, and when they have reached their lowest extremity N they have discharged their loops completely. The part M of the cam causes the needles to rise once more into their normal inoperative position, where they remain until the cams swing round to them again to resume the knitting operation. On the right of Fig. 51 will be noted a push-up cam in a dotted position PC1, and it should be explained that this is for the case of reciprocal knitting such as is required in making the heel or the toe of an article of hose. In this we operate only one-half of the needles in the cylinder, and in so doing cause the cams to move from side to side in an oscillatory fashion. When the cams are rotating in one direction push-up cam PC1 operates the needles, and when the direction of knitting is reversed PC gives the needles their upward thrust to receive the yarn. From Fig. 51 it will be clear that the depth of stitch drawn by the needle depends on the adjustment of the knitting cam KC, and the lower this is set the longer will be the loop drawn through. If the loop is required shorter so as to accommodate a larger number of courses per inch, the knitting cam is raised in its adjustment so that a shorter stitch is the result. The dial needles have a corresponding arrangement by which the needles are drawn farther in to make a longer loop and for a shorter loop are not pulled inwards to the same degree.

Making of a Ribbed Sock.—Fig. 52 gives a view of an ordinary type of sock where the various sections are marked as they are produced on the machine. A start is made with the rib top marked R which in this case is 1 and 1 rib, that is, one upright needle in the cylinder for every needle in the dial or ribber, and when all these are in operation at the same time 1 and 1 rib work is formed on the power stocking-knitter. Before beginning the rib top proper it is usual to make what is termed a welt which consists in working a number of courses in the upright needles only and letting the ribbed stitches draw round so as to give a finished appearance to the edge. On reaching the end of the rib top it is necessary to change the needle arrangement for making 3 and 1 rib, and in the case of the power-rib stocking-knitter every second needle in the upper ribber cylinder which is in the same plane as the lower one is made to slide into the lower cylinder, that is, we have three needles in the lower cylinder for every needle in the upper one. The 3 and 1 rib continues for the leg portion, as shown by Fig. 52, when arrangements require to be made for the heel-which has to be in the plain stitch and continued for the sole of the foot and round the toe. To effect the plain stitch for the heel, the front half of the dial needles are made to slide into the lower cylinder and fashioning for the heel is soon commenced. This is brought about by reducing the needles in work at each side one at a time until only about twelve needles are left in operation, when the process is reversed and the needles again brought into knitting position at each successive course until the full complement is available. This action gives a nicely-rounded pocket for the accommodation of the heel, and at the same time it is usual to introduce some form of reinforcing thread known as splicing, which has the effect of considerably increasing the period of wear of such articles. The plain stitch introduced for the heel is continued for the sole, where the top of the foot A is worked in rib stitch and the under portion B plain, as indicated in the diagram. When the foot has been worked in this manner to its full length, the reciprocating motion is repeated for the making of the toe exactly as for the heel, and several extra courses are inserted so that one article may be kept separate from another, and the next sock is worked exactly as the last. On the modern automatic rib sock machine about seven dozen pairs of men's socks can be produced by a single machine in a working day of eight hours, and as one girl can mind a set of half a dozen machines, it will be seen that the cost of production is infinitesimal when compared with hand-driven machines or with the hand stocking-knitter. One heavier item in the upkeep is the outlay required for a skilled mechanic, who is most essential if the machines are to be maintained in thorough working order, and this expense is proportionately the greater if the manufacturer has only a few machines in this department. It is essential to instal a series of machines of adequate scope of gauge and fineness to warrant the employment of a skilled mechanic who can repair and keep them in constant working order.

Full-fashioned Hosiery.—In addition to the large and important branch of the footwear trade which is devoted to the making of plain and ribbed articles devoid of seams and which comprise a large and important section of the knitting industry, we have other systems such as the full-fashioned hosiery trade which produce varied types of footwear. For full hose the length is greater, and as it has to cover the leg of the wearer right over the knee, it requires to be shaped to the fit of the individual. In the cheaper classes of hosiery an effort is made to introduce a diminution in the width of the leg towards the ankle by means of boarding, that is, the stockings are made uniform in width till nearly the ankle except for any small contraction which it is possible to effect by tightening the tensions. The woollen articles are stretched on boards carved to the shape of the leg and when dried in a heated chamber the natural plasticity of the wool enables the articles to take up the shape they have been stretched into, the wide portion of the leg stretches, whilst at the narrow portion the width contracts. Obviously this device cannot long stand the exigencies of wear, and after a short period of service the lower leg portion begins to widen and the result is most untidy. When one comes to consider the great trouble involved in making an article true to shape, it will be realized that such stratagems of quick manufacture mean a considerable saving of time.

As the name implies, full-fashioned hosiery is worked on the knitting frame in flat pieces which are afterwards seamed or joined together to form the article as required. For a full-fashioned hose in plain stitch, a rotary frame of the Cotton's Patent type is employed, and they are made with two articles in one normal division of the frame, that is, in a 12-at-once machine, for garment size we should be able to make twenty-four articles of hose at one and the same time. The leg is made uniform in width right down to the calf when narrowings are performed according to the rate of diminution required, but it is when the heel is reached that greatest labour is expended. It is necessary to work the heel in two sections at each side, and the foot sole is worked on to these pieces for the lower portion, the upper part of the foot being a continuation of the leg and the whole is secured by a seam along each side of the foot. By this system of manufacture it becomes possible to make a much more roomy and capacious heel than is general on the automatic seamless machine, for it can be made square-shaped and of any convenient size by enlarging or contracting the heel portions.

This method of manufacture is termed the English heel, but there is another system known as the French heel which is also largely adopted for certain classes of goods. The real test of these articles is to note the seam, which in the English foot always occurs along each side of the foot and down the back of the heel. In the case of the French foot the seam occurs along the centre of the sole of the foot which is obviously an awkward arrangement from point of view of comfort. The French style of foot is often employed for articles which have clocking or embroidered patterns on them, whilst there is also a saving of time in the process of making. The upper and lower portions of the foot are made in one width and afterwards folded over with only one seam along the middle of the sole of the foot, whilst in the case of the English foot the seam is double and occurs along each side of the foot. It is interesting to be able to distinguish between these various methods of making hosiery; for the article in which no effort is made to fashion the leg on the frame the marking indicative of narrowings for the leg will be entirely absent, and in their place will be the temporary local thickening of the fabric due to the increase in the number of stitches at that point. In the case of the full-fashioned article, the shape will be gradual and symmetrical, for the French foot only one seam will be found along the centre of the foot, whilst in the English variety a seam will occur at each side.