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).

[Illustration: 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The well known tapering needle bars of former years have been superseded by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.

[Illustration: 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.

Every effort is now made to reduce, as much as possible, not only the
extent of movement of the parts in high speed machines, but the weight of
the parts themselves. Indeed, so far has this been carried that, in some of
the Wheeler & Wil