The latch needle is one of the indispensable instruments of the knitting industry, as was abundantly proved during the war period when shortage of needles threw large numbers of useful knitting machines into disuse, whilst inferior needles accounted for a great drop in efficiency. There is a great variety in form of the latch needle, but they are similar in essential features. A sketch of a normal type is given in Fig. 8 where the various parts are lettered thus: H = hook at the left extremity of the needle, L = latch, S = stem or shank of the needle, B = needle butt or heel, as it is often termed. The latch moves on a pivot from the dotted position when it shuts the hook to the normal position when the hook is open. The stem or shank varies in proportion of length according to the class of machine in which it is employed, whilst there is also a large diversity of forms of the needle heel or butt usually in the direction of strengthening by adding extra metal to withstand friction for large scale knitting.

Loop Formation with Latch Needles.—The matter of loop formation is of the greatest interest and importance in any study of knitting and is shown in detail by means of a series of sketches, 1 to 5 in Fig. 9, illustrating the operation at the various stages. This will be useful in studying any knitting frame, for an apparently complex piece of machinery may be quickly reduced to intelligible dimensions if the observer has a grasp of the process of loop formation. All machines using the latch needle, and they are many and varied, form their stitch on exactly the same principle, and when this is understood considerable progress has been made towards a thorough comprehension of the whole. Sections 1 to 5 of Fig. 9 represent the successive stages in stitch making, the needles being shown at the angle usually found in the flat knitting machine of the Lamb type. In Diagram 1 of the series the needle is shown in its normal non-operative position with the latch closed and the loop M inside it. In all knitting a division must be maintained between the old loop and the new yarn. In Diagram 2 the needle rises, and in so doing the old stitch M opens the latch L and passes on to the stem and the new yarn marked Y is in the act of being seized by the hook of the needle. In Diagram 3 the needle is noted to have sunk lower in position so that the old loop M closes the latch with the yarn Y inside, and the old loop covers the latch as shown. This stage is termed the "landing of the stitch" and in Diagram 4 the needle is noted to have dropped still farther, so that the old loop is pushed over the needle extremity and the new yarn drawn through the old loop M to form a complete stitch. Precautions have to be taken in the machine mechanism to have the old loop properly discharged over the needle end and the new yarn completely drawn through. When this is complete the needle again rises in its position as in Diagram 5, and in so doing the yarn inside the hook moves downwards and opens the latch preparatory to a new course of stitches.

Diagram 10 illustrates another important form of the latch needle known as the double-headed needle as it has a hook at each extremity. This instrument forms the basis of utility of a series of different machines such as the rib hose frame and the pearl knitter. In these cases the needle moves from one knitting stage into another discharging its loop from the upper or lower hook according to the pattern of the rib or pearl fabric.

The Flat Knitter.—One of the best known machines using the latch needle for its loop formation is the flat knitter which has an extensive use in the knitting industry. The scope of work produced on the flat knitter is truly wonderful and its great versatility of application accounts for its immense popularity. In addition to plain fabric it can make a large variety of fancy and reinforced stitches, which provide great extension to the textural scope of the knitted fabric, allowing it to be employed for a wider diversity of uses. Various colours can be introduced in stripe formation, and with attachments of Jacquard character or by the use of the double-headed needle the range of patterns is further diversified. In regard to making full-fashioned goods almost every form of garment can be made on it-pants, shirts, hose and half-hose, coats, vestings, caps and gloves, are only a few of the garments procurable. These can be fashioned by the worker to the required form and an interpretation can be given to symmetry and style of the human form. It has found an extensive application as a hand machine to the making of seamless gloves being used by the most progressive firms in the trade, and with the application of power it can be adapted with considerable success to the making of goods in the bulk. Hand machines are moderately priced so that to start a knitting factory with such a plant is not a really formidable proposition, quite a respectable equipment being procurable for a few hundred pounds; many a prosperous firm owes its initial successes to the adoption of the flat knitter and from this they have been able to launch larger schemes of development in the knitting business. With new starters in this trade to-day the flat knitting machine nearly always figures prominently when there is lack of capital, and on this basis quite a sound foundation may be laid.

A diagrammatic side view of the Lamb flat knitting machine is shown in Fig. 11 where the foundation of the machine consists of two needle beds or stages marked NB which are cut with tricks or grooves into which the needles are placed as shown, each side being a duplicate of the other. The needle is marked N and on it will be recognized such essentials as the latch L, the hook H, the butt or heel B working inside the cam-box CB. The thread T passes from its bobbin through the eye of the thread-carrier TC and the needle is pushed into its position in the cam-box by the spring marked S shown at the extremity of the needle beds. The fabric is marked F and is noted to pass down through the centre of the machine whilst at its extremity is attached a set of weights which act as a means of drawing the fabric from the needle ends as they are formed and if the needles are not being sufficiently well cleared the amount of weight is increased. The weights have to be raised from time to time to a higher position in contact with the fabric as it is being worked.

Interior of Cam-box.—In this machine the principal functional part is the cam-box CB, and from this the knitting action is imparted to the needles. On this account a full view is given in Fig. 12 of the set of cams used in the knitting machine made by Messrs. W. and J. Foster of Preston. This set of cams is placed on each bed right and left and the constituent parts are indicated as follows. Parts A and B are termed the knitting cams, whilst the parts C, D and E combine to form what is known as the knock-up cam. The part E is a fixture, whilst the needle path is indicated curved, and through this the needle butts N are seen to be passing. From the previously-given description of the making of loops on the latch needle it should not be difficult to note that the cams working on the needle butts in the needle path combine to raise the needles to secure the yarn from the thread-carrier and, having received the yarn, the needles are pulled down again to complete the loop by drawing the new yarn through the old loop. The cams have a side-to-side motion and pass over the needle bed from right to left and again from left to right. In so doing they operate as follows: when the cam-box is passing from right to left the needle heels are made to ascend the left side of C and D and are drawn down again by the inside of cam B; when the action is reversed and the cam-box is drawn from left to right, the needle heels pass up the right side of cam D and are drawn down again by passing along the inside of cam A, this alternate action being repeated during the process of making plain work on the flat knitting machine.

The Rib Stitch.—One of the outstanding advantages of the flat knitter is the facility with which all kinds of rib stitches can be made, and this is due to the arrangement of the needle beds, where the needles of one side make their stitches in a direction contrary to those in the opposite side. In making rib work both sets of needles in back and front beds are in action at the same time; when the thread is supplied to the needles those on the back rise equally with those on the front and receive their share of yarn to form their own loops. Now it is clear that the knitting action on the right-hand needle is opposite in effect to that of a left-hand needle, this being expressed by the form of the knock-over of the stitch; the right-hand needles discharge their stitches to the left, whilst the left-hand needles discharge their stitches towards the right. It is this combination of stitches discharged in opposite directions which gives rise to the rib stitch which is such a valued adjunct to all forms of knitted texture. This difference in the direction of loop discharge causes one set of needles to form back-fabric stitches whilst the opposite needles knit right-side fabric stitches. The normal flat knitter has its two needle beds cut one-and-one, as shown in Fig. 13, each bed has accommodation for the same number of needles, these being set so as to pass up the centre between the opposite series. This is termed a one-and-one arrangement and the resulting fabric is known as the 1-and-1 rib stitch, one row of loops in a vertical direction appears as wrong-side fabric stitches, whilst the alternate rows work out as right-side fabric loops. This explains the great increase of elasticity found in rib texture as compared with plain because back-fabric stitches are always seeking the back. In their normal position they virtually pass to the back, only being visible on the face when stretch is applied in the width. The yarn in crossing from face to back and vice vers undergoes a greatly increased amount of intersection which contracts the whole fabric in the width. This property is of the greatest practical value in garment manufacture, because the extremities are usually finished with a few inches of rib which enables the article to secure a firmer hold on the limb or part of the body and thus serves to keep it in position. The rib stitch is also an indispensable foundation of a number of textures which weigh much heavier than the plain, as it enables a greater weight of yarn to be inserted and the fabric is thereby increased greatly in bulk.

Tension and Weight.—The texture of a fabric on any given knitting machine can be varied according to a number of factors and of these quite an important one is the length of loop drawn by the needle. An examination of Fig. 11 will show that the needle beds on the flat knitting machine are stationary and that the needles during stitch formation draw the yarn over the top ends of the beds and obviously the length of the loop will depend on the distance which the needle is drawn below the edge of the needle bed, this distance being determined by the adjustment of the knitting cams A and B shown in Fig. 12.

Cam B is shown in a dotted position raised so as to draw a shorter loop and the length of the loop can be varied according to the height of either knitting cams A or B within certain limits. If the loop is drawn too long, that is, if the knitting cam is set too deep, the yarn may not stand the strain and breakage will result; on the other hand, if the loop is too short the fabric will appear stodgy in character.

Patterns Produced.—This type of knitting machine has an extensive range of patterns and textures which can be obtained and amongst the first variations possible are those which result from an alteration of the needle arrangement. The normal setting is to have one needle in the front stage for one in the back stage, and these being arranged alternately give the ordinary 1-and-1 rib stitch. This is shown in Fig. 13, where the upper row of small circles represents the needles in the back bed or stage whilst the lower row gives those in the front stage. The next, Fig. 14, shows the needles in exactly the same sett except that the needles have been arranged to give the 2-and-2 rib pattern, this being shown in diagrammatic enlargement in Fig. 16 at the side. The third sett of needles given in Fig. 15 represents the arrangement for a 3-and-1 rib pattern where every third needle only is allowed to remain in the front stage whilst the back stage retains its full complement. From these examples it will be clear that by altering needles in this way to any scheme a large variety of rib effects may be produced, nor need the arrangement be uniform throughout the width, for the borders may be in one pattern and the ground or interior in another. Novel effects in imitation of lace work may also be produced by leaving a needle out of one or other of the beds which makes an opening in the fabric which can be manipulated to give an effect of a lace-like character.

Manipulation of Knitting Cams.—Figs. 17 to 20 have been prepared to illustrate the manner in which the cams are altered to give certain well-known stitches in the flat knitting machine, and the construction is the same as Diagram 12, with corresponding letters for the various parts. On the left of the plate are arranged the cams as in the front bed whilst the right-hand arrangement gives the set of the cams in the back. In Fig. 17 the two beds are shown arranged for plain rib work where both back and front needles are in action at the same time. Fig. 18 shows the cam setting in front and back beds for making the well-known half-cardigan or royal rib which has played such an important part as the stitch for cardigan jackets supplied to the troops during the war period. It will be seen that on the front bed cam A is raised into what is termed a tucking position, that is, the needles are pushed up by D to receive the thread but are not drawn down far enough to have their loops discharged over the needle ends. At the same time the cams in the back bed are set for plain work and the needles there knit as usual at every course. The real stitch, however, does not appear until the direction of knitting is reversed, because the needles on the front bed are again pushed up to receive a second thread and on this occasion are drawn down the full distance by B to knock off the stitches. This means that on the front bed stitches are formed in double threads after every two courses whilst the back discharges its loops at every course, which enables a much greater weight of yarn to be inserted into the texture, making it more rigid and stable. The cams in Fig. 19 are arranged in front and back beds to produce the polka or full cardigan stitch, where double courses are worked on both front and back. This may be clear if we consider the cam arrangements as illustrated moving first to the right when the stitches on the front bed are "tucked" whilst those on the back bed knit to the position of cam A. In reversing the knitting to proceed to left, two yarns are drawn through in the front needles whilst no discharge takes place on the back. In this way the knitting occurs on the cardigan rib plan on both front and back needle beds and the resulting fabric is much heavier in weight than half-cardigan and when taken from the machine shows a strong tendency to expand in width owing to the yarn seeking to take up a more expanded position. The full cardigan stitch tends to be loose in character, the weight of material is greatly increased over plain 1-and-1 rib, but there is a lack of structural firmness and cohesion. In Fig. 20 the part C of the cam comes into the picture as being necessary to give circular work on the flat knitting machine. This can be drawn up out of action in both front and back beds by a small finger lever, and an examination of this arrangement will show that in going to the right the needles of the front bed will knit as usual, but in reversing, as shown on the right of Fig. 20, the needles pass completely under part D owing to the absence of part C and knitting is not performed; the cam portion D is raised by a spring to allow the needles to pass over the dotted position. It will thus be seen that to make circular work we arrange the cams on the front bed so that they will knit in going to right but miss in going to left, whilst in the opposite bed the reverse holds good. Thus a course of loops is made on the front with the back not knitting, alternated by a course made on the back with the front not knitting. The fabric's being worked from one yarn causes the loops to be joined at the edges and so a continuous length of circular webbing is produced.