Compensation has been attempted here and there in the machines for many years, but no sewing apparatus could be said to be so compensated until the cone compensator came into use, a device which has been taken advantage of by various makers. Save in the shuttle race itself there is not a part of the oscillating shuttle machine subject to serious wear that cannot be instantly adjusted to full motion by the turning of a screw, while wear in the shuttle race can be compensated for in the usual way. This effective system depends upon the union of two mathematical forms, long used in mechanism—the cone and the screw. In screw cones we possess a perfect compensator, and it is surprising that parts of mechanism so hung appear subject to very little wear. Another advantage, too, is gained by the introduction of screw cone bearings; the friction is always greatly reduced by their use. In every case the fine adjustment of the cones is securely maintained by locknuts (Fig. 7).
FIG. 7.
But the screw cone system is not the only compensator used in sewing machinery; where it cannot be easily introduced, other devices have been employed.
The well known tapering needle bars of former years have been superseded by cylindrical needle bars. The Wheeler & Wilson Company appear to be the first who utilized the engineer's shifting box as an antifriction device for round needle bars. They packed their bars round with felt rings, and compressed the whole by a screw cap.
In the Singer machines the same excellent device has been adopted, hemp packing and screw bushes being used (Fig. 8); f and g show the direct action on the needle bar. This method of forming needle bar bearings, partially of metal and partially of felt or hemp, has afforded the most surprising results.
FIG. 8.
When the bars are of hard or finely polished steel, no perceptible wear can be detected in them, even after they have been in daily use in factories for twelve months, whereas bars not so bushed might show considerable wear in that space of time. The packing, to be effective, should be sufficiently close to prevent as much as possible friction of the steel with the cast iron needle bar ways. Lubrication of the steel is insured by keeping the hemp packing moistened with oil.
Cylindrical needle bars, when combined with an effective system of brushing, have proved themselves superior to every other form of slide for lock stitch machines. But their introduction is by no means a thing of yesterday. They were used freely in sewing machines as far back as 1860, but were never very successful until united with the lubricating brush. Some makers go a step further, and elaborate the system by the introduction of steel brushes, easily renewable.