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Basic Machines - Intro to machines and motion theories | Next
Summary |
Figure 5-5.—A turnbuckle.
Figure 5-6.-A rigger’s vice.
Because you can make accurate measurements
with this instrument, it is vital in every machine
shop.
APPLICATIONS AFLOAT AND ASHORE
It’s a tough job to pull a rope or cable tight enough
to get all the slack out of it. However, you can do it by
using a turnbuckle. The turnbuckle (fig, 5-5) is an
application of the screw. If you turn it in one
direction, it takes up the slack in a cable. Turning it
the other way allows slack in the cable. Notice that
one bolt of the turnbuckle has left-hand threads and
the other bolt has right-hand threads. Thus, when
you turn the turnbuckle to tighten the line, both bolts
tighten up. If both bolts were right-hand thread-
standard thread-one would tighten while the other
one loosened an equal amount. That would result in
no change in cable slack. Most turnbuckles have the
screw threads cut to provide a large amount of
frictional resistance to keep the turnbuckle from
unwinding under load. In some cases, the turnbuckle
has a locknut on each of the screws to prevent
slipping. You’ll find turnbuckles used in a hundred
different ways afloat and ashore.
Ever wrestled with a length of wire rope?
Obstinate and unwieldy, wasn’t it? Riggers have
dreamed up tools to help subdue wire rope. One of
these tools-the rigger’s vise-is shown in figure 5-6.
This rigger’s vise uses the mechanical advantage of
the screw to hold the wire rope in place. The crew
splices a thimble-a reinforced loop—onto the end of
the cable. Rotating the handle causes the jaw on
Figure 5-7.—A friction brake.
Figure 5-8.—The screw gives a tremendous
mechanical advantage.
that screw to move in or out along its grooves. This
machine is a modification of the vise on a workbench.
Notice the right-hand and left-hand screws on the
left-hand clamp.
Figure 5-7 shows you another use of the screw.
Suppose you want to stop a winch with its load
suspended in mid-air. To do this, you need a brake.
The brakes on most anchor or cargo winches consist
of a metal band that encircles the brake drum. The
two ends of the band fasten to nuts connected by a
screw attached to a handwheel. As you turn the
handwheel, the screw pulls the lower end of the band
(A) up toward its upper end (B). The huge mechanical
advantage of the screw puts the squeeze on the drum,
and all rotation of the drum stops.
One type of steering gear used on many small
ships and as a spare steering system on some
larger ships is the screw gear. Figure 5-8
shows you that the
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