Figure 5-5.—A turnbuckle.Figure 5-6.-A rigger’s vice.Because you can make accurate measurementswith this instrument, it is vital in every machineshop.APPLICATIONS AFLOAT AND ASHOREIt’s a tough job to pull a rope or cable tight enoughto get all the slack out of it. However, you can do it byusing a turnbuckle. The turnbuckle (fig, 5-5) is anapplication of the screw. If you turn it in onedirection, it takes up the slack in a cable. Turning itthe other way allows slack in the cable. Notice thatone bolt of the turnbuckle has left-hand threads andthe other bolt has right-hand threads. Thus, whenyou turn the turnbuckle to tighten the line, both boltstighten up. If both bolts were right-hand thread-standard thread-one would tighten while the otherone loosened an equal amount. That would result inno change in cable slack. Most turnbuckles have thescrew threads cut to provide a large amount offrictional resistance to keep the turnbuckle fromunwinding under load. In some cases, the turnbucklehas a locknut on each of the screws to preventslipping. You’ll find turnbuckles used in a hundreddifferent ways afloat and ashore.Ever wrestled with a length of wire rope?Obstinate and unwieldy, wasn’t it? Riggers havedreamed up tools to help subdue wire rope. One ofthese tools-the rigger’s vise-is shown in figure 5-6.This rigger’s vise uses the mechanical advantage ofthe screw to hold the wire rope in place. The crewsplices a thimble-a reinforced loop—onto the end ofthe cable. Rotating the handle causes the jaw onFigure 5-7.—A friction brake.Figure 5-8.—The screw gives a tremendousmechanical advantage.that screw to move in or out along its grooves. Thismachine is a modification of the vise on a workbench.Notice the right-hand and left-hand screws on theleft-hand clamp.Figure 5-7 shows you another use of the screw.Suppose you want to stop a winch with its loadsuspended in mid-air. To do this, you need a brake.The brakes on most anchor or cargo winches consistof a metal band that encircles the brake drum. Thetwo ends of the band fasten to nuts connected by ascrew attached to a handwheel. As you turn thehandwheel, the screw pulls the lower end of the band(A) up toward its upper end (B). The huge mechanicaladvantage of the screw puts the squeeze on the drum,and all rotation of the drum stops.One type of steering gear used on many smallships and as a spare steering system on somelarger ships is the screw gear. Figure 5-8shows you that the5-3
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