By JOHN W. URQUHART.
The distinct improvements in sewing machinery to which I would invite your attention this evening have reference more particularly to the results of inventive effort within the past ten years. But although marked development in the machines has occurred in so short a time, it may be taken for granted that those advances are but the accumulated results of many years' prior invention and experience of stitching appliances.
The history of the sewing machine, and the decision of the great question, Who invented an apparatus that would unite fabrics by stitches? do not at present concern us. Many sources of information are open to those who would decide that extremely involved problem. But whether the production of the first device of this kind be claimed for England or for America, it is quite certain that no one man invented the perfect machine, and that those fine specimens of sewing apparatus shown here to-night embody the labors of many earnest workers, both in Europe and America.
Most of us are familiar with the arrangements of an ordinary lock stitch machine, and an able paper by Mr. Edwin P. Alexander, embracing not only a good account of its history, but most of the elements of the earlier machines, has already (April 5, 1863), been read before you. This, and sundry descriptions of such apparatus in the engineering papers, confine my remarks to the more recent improvements in three great classes of machines. These are, briefly, plain sewing machines; sewing machines as used in factories, where they are moved by steam power; and special sewing machines, embracing many interesting forms, only recently introduced. We have thus to consider, in the first place, the general efficiency of the machine as a plain stitcher. Secondly, its adaptability to high rates of speed, and the provision that has been made to withstand such velocities for a reasonable time. And, thirdly, the apparatus and means employed to effect the controlling of the motive power when applied to the machines.
To deal with the subject in this way must, I fear, involve a good deal of technical description; and I hope to be pardoned if in attempting to elucidate the more important devices, use must be made of words but seldom heard outside of a machinists' workshop.
It appears scarcely necessary to premise that the sewing machine of twenty years ago has almost faded away, save, perhaps, in general exterior appearance; that the bell crank arms, the heart cams, the weaver's shuttles, the spring "take ups," rectangular needle bars, and gear wheels, have developed into very different devices for performing the various functions of those several parts.
The shuttle is perhaps the most important part of a lock stitch machine. But what is a shuttle? So many devices for performing the functions of the early weaver's shuttle have been introduced of late, that the word shuttle, if it be used at all, must not be accepted as meaning "to shoot." We have vibrating shuttles, which are, strictly speaking, the only surviving representatives of the weaver's shuttle in these new orders of machines; and stationary shuttles, oscillating shuttles, and revolving shuttles, besides the earlier rotating hook, in several new forms, difficult to name. But the general acceptation of the word shuttle, as indicating those devices that pass bodily through the loop of upper thread, is, I venture to think, sufficiently correct.
Many changes have been effected in the form, size, and movements of the shuttle, and we may profitably inquire into the causes that have induced manufacturers to abandon the earlier forms. The long, weaver's kind of shuttle, originally used by Howe and Singer, had many drawbacks. Mr. A.B. Wilson's ingenious device, the lock stitch rotating hook, was not free from corresponding faults. The removal of these in both has led to the adoption of an entirely new class of both shuttles and revolving hooks. It is well known that the lock stitch is formed by the crossing of two threads, one of which lies over, and the other under, the cloth to be sewn. This crossing point, to insure integrity of the stitch, must occur as nearly as possible in the middle of the thickness of the fabric. The crossing must also be effected while a certain strain, called tension, is imposed upon both threads. If the tension of one thread should outweigh that of the other, the locking point becomes displaced. If the tension be insignificant, the stitches will be loose.
If the tension should vary, as in the long shuttle, there will occur faulty points in the seam.
In the earlier rotating hook the tension depended upon the friction developed between the spool and the hook. This tension, therefore, varied in proportion to the speed of the latter, and could never be constant. This was quite apart from the frictional resistance offered to the upper thread in passing over the cavity of the hook.
In the shuttle the tension was obtained by threading through holes in the shell, or beneath a tension plate, as in Howe's machine. This tension, so long as the reel ran between spring centers, was never constant. The variation was chiefly due to the angular strain set up when unwinding from the reel. This strain varied according to the point of unwinding. It was light in the middle of the reel and heavy at either extremity. These drawbacks caused immense anxiety to the first makers of sewing machines, and numerous attempts to overcome them led to little improvement. With reference to high rates of speed, the older shuttle, requiring a long and noisy reciprocation, had its disadvantages.
The only effective remedy for these drawbacks was a radical one. It was necessary to substitute depth of reel for length. Hence, several attempts have been made to construct disk or ring shuttles. Many forms of those have been tried. They all depend upon the principle of coiling up the thread in a vertical plane, rather than in horizontal spirals. Some makers placed the disk in a horizontal plane, and caused it to revolve. Nothing could be worse, as will be seen, if we follow the course the enveloping loop must take in encircling such a shuttle. But a complete solution of the difficulty of employing a ring shuttle has been achieved in the oscillating form, invented by Mr. Phil. Diehl, and known as Singer's (Fig. 1). A short examination of it may profitably engage your attention. The shuttle itself is sufficiently well known, but certain features of it, and to which it owes its efficiency, appear to call for some explanation. Its introduction dates back some years, during which time it has undergone certain modifications.