This section is from the book "The Manufacture Of Boots And Shoes: Being A Modern Treatise Of All The Processes Of Making And Manufacturing Footgear", by F. Y. Golding. Also available from Amazon: The Manufacture Of Boots And Shoes.
The action of a sewing-machine depends upon the loops that are thrown out by the needle. Needles for leather work have two grooves, rendered necessary to carry through the thread, owing to the tendency of the material to close after piercing.
One of the grooves is longer than the other, and when setting the needle in the needle - bar, the long groove (Fig. 197, A) should be away from the point of the shuttle or hook. The short groove (Fig. 197, B) should always face the shuttle or hook point. The throwing of the loop (Fig. 197, C), for the looper shuttle or hook to enter, is performed by the latter groove. Similarly, when threading up, always thread from the long to the short groove (Fig. 197, D). The long groove protects the thread from undue injury during its passage through the material. Sufficient sewing material must be paid out through the eye of the needle to form a loop large enough for the shuttle or hook to pass through. After the passage, the thread must be again drawn through the eye of the needle, so that it is subjected to friction caused by the passing to and fro of the thread. The eye of the needle must therefore be perfectly smooth, and as large as possible in relation to the size of the needle.
If the needle eye be too large for the size of the thread, the machine will miss stitches; and similarly, if it be too small, the thread will be broken.
In most of the machines the needle is self-setting, and in such cases the shank should be inserted right to the top of the hole in the needle-bar. In the machines illustrated in Figs. 221 and 222, the needle should be set to the file-mark on the needle-bar. Care should be taken with the hook machines that the needle is set correctly, because if too low it is likely to damage the hook. When correctly set, it should have the same relation as that shown by Fig. 198.
When a rotary presser-wheel is used the threading may be facilitated by placing the end of the thread in the groove of the needle, and lowering the end until it enters the eye, as illustrated by Fig. 199.
When extra hard twisted thread is employed, it is sometimes advisable to slightly turn the needle, so that the loop may be thrown squarely on the hook of the shuttle. A reverse twist in the thread will be treated in a similar way, but the needle will be slightly turned in the other direction.
The point of the needle must be sharp, and for leather work the points are chisel-shaped, instead of taper or round, as those used for fabric. The chisel-shaped or flat point is variously positioned in relation to the direction of the eye of the needle. The direction of the cutting or piercing point of the needle in relation to the line of stitching very largely determines the appearance of the stitch when deposited in the work. For various kinds of work differently pointed needles are selected. For a "pearly" stitch the point used is one that spreads the stitch and punctures the leather more or less transverse to the line of stitching; but for a sunken stitch for heavy or stout work, or for work that has to be "hammered off," a needle that cuts the slit parallel to the line of stitching is required.
For cloth, linings, fabrics, and sometimes for light leathers, a needle with a round point ( • ) is used. This kind of needle is also advisable for stitching elastic gussets. Needles that perforate thus / are used for work where the stitch is required to be well drawn to the leather. When a face stitch is required, giving what is sometimes known as a "pearly " stitch, a point is selected that makes a cut thus - . If the stitch is required to be more sunken than the point that cuts, points should be used that puncture thus |.
Various names are given by the makers for the points of their needles ; for instance The " W. & W." names areReverse. Flat. Cross flat. Spear. O.S. Twist. Twist.
That cut ---- / and used for Face Sunk stitch. Sunk stitch. Sunk stitch. Sunk stitch. stitch.
The "Singer " names are Bound. Twist. Reverse. Wedge. Cross.
That cut # ---and used for Elastic Sunk Drawn Flowering or Sunken and fabric. stitch. stitch. face stitch. more than "reverse."
The Bradbury Co. use the following:Flat or chisel. Twist. Cross.
that cut the point of the needle may be named in reference to the direction it takes in relation to the needle-eye plane, and would be as follows :-
The size of a needle is known by a number, but unfortunately there is not that uniformity in size desirable among the makers. This can be seen by making a few tests,* either using Stubbs' gauge or a micrometer. Perhaps this variance partly accounts for the fact that, with a given number of needle, various closers employ various sizes of stitching material. The point to bear in mind when selecting a needle to use with a given "thread," is to choose one that punctures a hole that will be well filled up when the thread is deposited in its place. The nature of the stitching material will also influence the selection, as the softness of silk will enable a smaller-sized needle to be used when compared with a similar substance thread.