SEWING MACHINE 801 FIG. 2. Four-motion Feed. which the cloth is fed, in the direction of the four sides of a parallelogram. The teeth carry the cloth forward while moving horizontally a short space above the surface of the plate ; the bar then drops (the second motion), then passes backward horizontally beneath the plate (the third motion), and rising brings the teeth through the slot and above the surf ace (the fourth motion). The I ' - ^ - 1 1 directions of these motions are indi- Cated in fig. 2. The motion which carries the cloth forward is so timed by cams upon a wheel, or by eccentrics or other devices, as to take place while the needle is raised above the cloth, and never to interfere with its pas- sage. The four motions are obtained in the Willcox and Gibbs machine by a single eccen- tric, and the number of stitches to the inch may be determined by a device which em- ploys a dial with numbers upon it, showing through an opening in the cloth plate. Most of the sewing machines now in use are lock- stitch machines, the stitch being precisely the same in all, and the principle upon which it is formed being nearly the same also. It is al- ways made by passing loops of thread through FIG. 8. Lock Stitch. the fabric, by means of an eye-pointed needle, and then passing another thread through these loops, this latter part of the process being usu- ally produced by means of a shuttle which is made to pass through the loops. "When the shuttle thread is pulled back half way through the fabric, the stitch has the construction shown in fig. 3, where the threads are raised from the cloth to give a better view. It will be seen that the position of either thread is the same in relation to either side of the cloth ; but when the loops formed by the needle are not drawn into the body of the fabric, the shuttle thread will lie straight on the under side of the cloth, as shown in fig. 4. The manner of making FIG. 4 Lock Stitch. the stitch with the shuttle is shown in fig. 5. In most machines the needle vibrates in a right line, being carried by a vertically mov- ing needle bar which slides in grooves. A shuttle bar carrying a shuttle underneath the cloth plate is made to pass through the loop, which opens to receive it when the needle be- gins to retract. The two bars, the needle bar and the shuttle bar, being actuated by the same motor, are so adjusted that their times of motion exactly correspond to each other. The shuttle, passing backward with its bobbin while the loop is drawn up into the cloth, only carries its thread through the loops in one direction, and unwinds just as much thread at each passage as corresponds to the curved FIG. 5. Shuttle. length of the thread necessary to form a stitch. It is prevented from unwinding more than this by haying the thread held by a device called a tension. The thread which is delivered by the needle is also held in the same way, in con- sequence of which the loop is retracted when the needle is drawn upward, the degree of retraction depending upon the tension, or the tightness with which the thread is held. The celebrated Singer and Howe machines are of this class, as also the well known Weed, Do- mestic, Florence, Remington, Wilson, Ameri- can, Secor, and others. The Florence machine differs from the other lock-stitch machines in having a curved needle attached to the end of a vibrating arm, instead of being carried by a needle bar moving vertically in guides ; and there are various ways of actuating the needle bars in all of them. Another form of lock- stitch machine, instead of causing a shuttle or movable bobbin to pass through the loop FIG. 0. FIG. 7. formed by the needle, catches this loop by means of a rotary hook and passes it over a stationary bobbin, which answers to the mova- ble shuttle, and may be regarded as a station- ary shuttle. The lock stitch of the Wheeler and Wilson machine may be made by hand, and its formation explained by reference to Bg. 6. Take a piece of fabric, c, an ordinary needle, A, threaded with e, and a small ball of thread, /; tie the ends of the two threads together, thrust the needle threaded head first ihrough the fabric, and instead of passing the ball of thread through the loop e, hold the ball and pass the loop around it; withdraw the needle and draw the interlocked portion of the
- hreads, e and 2, into the fabric. A succession
of stitches thus made will form a seam. The ock stitch is formed by the machine in an
