CHAPTER V

THE DOUBLE LOCK FLAT MACHINE—HOW DIFFERENT STITCHES ARE FORMED

Our study of flat machines up to this point has dealt entirely with the class known as the single lock machines, or those that have but one set or pair of locks to do the knitting. There is another very popular type, commonly known as the double-lock machine, which is, it might be said, in a class by itself. This machine, as the name would indicate, has two sets or pairs of locks mounted on the same carriage, and set as closely together as they can be and work properly.

The double-lock machine has many advantages over the single-lock type, the most important being that there can be made upon it a two-faced fabric, that is, a fabric with each side faced with a different yarn, either in color, quality or both. The popular “cotton back” sweater is in this class. In making this class of fabric it is essential that the two different yarns, to show out on the two faces of the fabric, go into the fabric in alternate courses. Therefore, it is obvious that it would not be practical to make this fabric on a single lock machine, for when a course was finished the second yarn would be on the opposite end of the machine from the locks and yarn carrier, and it would be necessary to put on a full round, or two courses, in order to get back to that end to exchange yarn carriers.

The double-lock machine overcomes this difficulty by taking both yarn carriers across, one following the other, each on a pair of locks, each time the carriage moves across the machine. It is evident from this that every time the carriage is moved across the machine there are two courses put on the fabric, instead of one as with the single-lock machine.

Speed and Production

This point leads up to another advantage of the double-lock machine, that is, increased production on account of putting on two courses with each movement of the carriage across, as against one course with the single-lock machine. The production would not be twice as much, as might be supposed at first thought, for comparing two machines of the same size, the single lock could be operated at a greater speed than the double lock, but not approaching twice the speed. The reason for this is that the locks of the double-lock machine must, of course, be practically twice the length of the locks of the single-lock machine, and inasmuch as the locks must move far enough at each end to be clear of or past the needles, it is quite obvious that the double-lock carriage must have a longer travel. Therefore, it takes longer to complete one round of the carriage than the single-lock machine, to maintain the same needle speed.

This brings us to another point that may as well be disposed of here, and that is the speed of latch needle machines. Generally speaking, the maximum speed of a latch needle machine, either flat or circular, is governed by the needle speed; that is, the speed at which the cams raise and lower the needles, and the thread velocity, which is of course dependent on the needle speed.

Speed of Flat Machines

As a general rule, where the machine is in good condition and the yarn of fairly good quality, a flat machine with a crank drive should be operated at from 100 to 125 lineal feet per minute, and a chain drive may be operated at from 125 to 150 lineal feet per minute. The reason for this difference between the chain drive and the crank drive is that with the crank drive the movement of the carriage across the machine is not uniform throughout, its movement being faster in the center than at either end, therefore we must regulate our speed so it will not be too high at this point. On the other hand, the chain drive carries uniformly throughout the movement of the carriage except for two or three inches at the ends.

To explain what is meant by lineal feet per minute, let us assume that we have a 20-inch machine, that is, there are 20 inches of needles. In this case the carriage would have to travel about 30 inches on account of the locks having to clear the needles at both ends, therefore a movement of the carriage across and back, or one complete round, would cover twice 30 inches or 60 inches, or 5 feet. Now if we intend to run this machine at a speed of 120 lineal feet per minute, we would divide 120 feet by 5 feet, which would give us 24 rounds per minute, the speed the machine should run.

I do not wish to be understood as giving this as a hard and fast rule for the speed of machines, for there are many factors which enter into the operation of knitting machinery which might make it desirable to vary this speed. Some of these factors are the condition of the machine, the experience of the operator, the character of the yarn, the class of fabric, and sometimes the skill of the mechanic in charge of the machines.

Going back to the two-faced fabric, this must be made on one of the two cardigans. The “cotton backs” are usually made on the half cardigan, while the fabrics with two different colored faces are made on the full cardigan as a rule.

Fig. 40 shows a type of double lock used in a Dubied machine made in Switzerland. The reader will understand from what has gone before that this illustration shows the locks turned upside down, that is, if they were in operation on a machine they would be turned over with the cams close to the needle plates. It will be noted that the fundamentals are the same as in the Lamb system previously described, but the method used to change from the plain rib to the full or half cardigan, or vice versa, is different.

In making a plain rib fabric the needle butts would follow the camway as in the Lamb system, that is, if the carriage were being moved from left to right the needle butts would follow the course up with cams 1_a_, 1_b_ and 1_c_ below, and 1, 1_s_, 8_s_ and 8 above. This explanation would of course apply to all four sets of cams. The cams 1_b_, 2_b_, 3_b_ and 4_b_ have studs which project through the cam plate and there are means provided to draw any one or all of these cams back through the cam plate by these studs far enough so that the faces of the cams are flush with the cam plate, and entirely out of operation.

The cams 1_c_, 2_c_, 3_c_ and 4_c_ are made to swing on the pivots, _aa_, and are held down on cams, 1_a_ to 4_a_, in the position shown, by springs. It should be particularly noticed that the cams just mentioned, 1_b_ to 4_b_, and 1_c_ to 4_c_, are exactly alike in the four sets of locks, but their positions are reversed in the sets opposite. They are placed in this way in order to facilitate the making of the cardigan stitches.

Making Half Cardigan Stitch

In the study of what follows it should be remembered that the illustration at Fig. 40 shows the locks bottom up, therefore in actual operation the lower set in the illustrations would be the back ones, and the upper set the front ones.

In making the half cardigan stitch it is customary to have the tuck or holdover stitch on the back plate; on the double-lock machine, where we have two feeds, it is on the back feed, and the plain course is on the locks that are leading. Therefore, to make a half cardigan stitch with these locks we would simply raise cams 2_b_ and 3_b_ up through the cam plate out of working position.

Now remembering that the cams 2_c_ and 3_c_ are free to swing up and down on the pivots, _aa_, and are held down in their present position by a small spring, it should be readily understood that in moving the carriage from, let us say, left to right, the butts of the needles would follow up the right side of cam 2_a_, and on up over 2_c_, therefore would knit out on this course. But when these butts came to the second set of locks they would move up the right side of cam 3_a_ until they came to the upper right hand corner of this cam, and at this point, on account of cam 3_b_ being up out of operation, they would move across and raise up cam 3_c_ and pass under it. Cam 3_a_ not being high enough to raise the needles to the point where the stitch would drop off the latches, obviously the needles must hold the two stitches on this side of these locks.

On the return of the carriage from right to left the operation of the needles would be reversed, that is, they would pass up over cam 3_c_ and knit out on the locks in the lead and pass under cam 2_c_.

To sum up the whole operation in a few words, to make a half cardigan stitch we must alternate with the plain rib course and a course that tucks or holds the previous stitch, as well as the new one on one side. This half cardigan is the stitch used in making what is known as the “cotton back” sweater and other such fabrics.

By having one yarn carrier threaded with cotton and one threaded with wool or worsted, as the case may be, and changing these carriers at the end of every course so as to keep the cotton always knitting at the cams that are leading or making the plain stitch, the cotton alone will draw through on the back of the fabric while the worsted or wool will practically cover the face stitch of the cotton. This exchange of the yarn carriers at the end of each course is done automatically by the machine, therefore requires no attention by the operator.

Full Cardigan Stitch

To make the full cardigan stitch the procedure would be practically the same as explained on the single-lock machine, as both pairs of these locks would be tucking or holding on one side (opposite sides) on one course, and each would reverse itself on the return course. The cams 1_b_, 2_b_, 3_b_ and 4_b_ would be lifted up out of operation. When this is done the cams 1_c_, 2_c_, 3_c_ and 4_c_ would operate automatically to give us this result. This is the stitch used as a rule to make the two-faced fabrics, that is, to make the two sides of different colors.

In connection with this explanation the question may arise as to why the half cardigan stitch is used in making a fabric with one side cotton and the other side wool or worsted, and the full cardigan stitch used when making the two sides of different colors. The answer to this is that the half cardigan stitch makes the better fabric of the two for most purposes on account of the face stitch being full and round, thereby filling up the space between the wales. Inasmuch as the cotton stitch on the face is very short, and the wool or worsted quite long, and both are the same color, the cotton will show but very little, if any. On the other hand, if two widely divergent colors were used, the face would not show a solid color but would have more of a salt and pepper effect.

To go back to Fig. 40 it will be noted, as stated before, that while the principle of these locks is the same as the Lamb system previously explained, the construction is somewhat different. The stitch cams, 1, 8, 7, 6, 3 and 4 are shaped along the lines of a parallelogram, while all the stitch cams in the Lamb system were triangular. Cams 3 and 4 are made this shape to allow placing the triangular cam, 1_d_, in position to act as a guard cam to prevent the butts of the needles from flying up between after dropping off the ends of the stitch cams 3 and 4. Yet it allows these stitch cams to be moved freely up and down through the angular slot in the cam plate, which shows at the ends, in order to make the stitch longer or shorter as the need may be. Cams 1 and 6 are made this shape to allow placing back of them the triangular cams 9 and 10, but these are for another purpose.

It sometimes happens that it is desirable to make a fabric with the stitch so short that it would not cast the old stitch off over the end of the needles with all the cams set high enough to make this short stitch. When this is the case, cams 1 and 6 only would be moved up to a point where they would not draw the new stitch through the previous one on their respective courses, therefore would not use any yarn, while the opposite cams 2 and 5 would draw a full stitch.

After the needles had passed these cams (2 and 5) the cams 9 and 10 on their respective courses, having been set down to the proper position, would draw the needles in this plate down to the point where the old stitch would cast off, thereby completing that stitch without undue strain on the yarn on account of the needles on the opposite side being free to raise far enough to prevent it. Cam 11 acts as a guard cam for 7 and 8 and also is used on a short stitch to cast off for these two cams, the same as 9 and 10 cast off for 1 and 6.

Yarn Carrier for Plating

Fig. 41 shows a yarn carrier used for plating on a flat machine. By plating is meant where two threads of different quality, say worsted and cotton, are used in the same course, and the worsted is laid in the fabric so as to show on the outside and the cotton is in the middle. To do this the worsted yarn, _d_, _d_, would pass through the center hole, _b_, and the yarn _c_, _c_, passing through the crescent-shaped hole, _a_, would be the cotton. It will be noted that the angular draw of the yarn from the bottom of the guide into the needles will always keep the yarns in the positions shown. When the end of the course is reached, and the movement of the carriage is reversed, the cotton yarn _c_, _c_, will swing around to the opposite end of the crescent-shaped hole, _a_, and in this way will always be in the same relative position to the worsted yarn _d_.