CHAPTER 6 RIGGING
Rigging is the method of handling materials using fiber line, wire rope, and associated equipment. Fiber line and wire rope were discussed in chapters 4 and 5. We will now discuss how these materials and equipment can be used in various tackle and lever arrangements to form the fundamental rigging necessary to move heavy loads. Additionally, we discuss the makeup of block and tackle, reeving procedures, and common types of tackle arrangements. Information is also provided on other common types of weight-handling devices, such as slings, spreaders, pallets, jacks, planks and rollers, blocking and cribbing, and scaffolds.
SAFETY is paramount in importance. You will be briefed throughout this chapter on safety measures to be observed as it pertains to the various operations or particular equipment we are discussing. Also, formulas are given for your use in calculating the working loads of various weight-moving devices, such as hooks, shackles, chains, and so on. SAFE rigging is the critical link in the weight-handling process.
BLOCK AND TACKLE
The most commonly used mechanical device is block and tackle. A block (fig. 6-1) consists of one or more sheaves fitted in a wood or metal frame supported by a shackle inserted in the strap of the
Figure 6-1.-Parts of a fiber line block.
block. A tackle is an assembly of blocks and lines used to gain a mechanical advantage in lifting and pulling.
The mechanical advantage of a machine is the amount the machine can multiply the force used to lift or move a load. The strength of an individual determines the weight he or she can push or pull. The ability to push or pull is referred to as the amount of force the individual can exert. To move any load heavier than the force you can exert requires the use of a machine that can provide a mechanical advantage to multiply the force you can apply. If you use a machine that can produce a push or pull on an object that is 10 times greater than the force you apply, the machine has a mechanical advantage of 10. For example, if the downward pull on a block-and-tackle assembly requires 10 pounds of force to raise 100 pounds, the assembly has a mechanical advantage of 10.
In a tackle assembly, the line is reeved over the sheaves of blocks. The two types of tackle systems are simple and compound. A simple tackle system is an assembly of blocks in which a single line is used (fig. 6-2, view A). A compound tackle system is an assembly of blocks in which more than one line is used (fig. 6-2, view B).
Figure 6-2.-Tackles: A. Simple tackle; B. Compound tackle.
The terms used to describe the parts of a tackle (fig. 6-3) and various assemblies of tackle are as follows:
• The block(s) in a tackle assembly change(s) the direction of pull, provides mechanical advantage, or both.
• The fall is either a wire rope or fiber line reeved through a pair of blocks to form a tackle.
• The hauling part of the fall leads from the block upon which the power is exerted.
• The fixed (or standing) block is the end which is attached to a becket.
• The movable (or running) block of a tackle is the block attached to a fixed objector support. When a tackle is being used, the movable block moves and the fixed block remains stationary.
• The frame (or shell), made of wood or metal, houses the sheaves.
• The sheave is a round, grooved wheel over which the line runs. Usually the blocks have one, two, three, or four sheaves. Some blocks have up to eleven sheaves.
• The cheeks are the solid sides of the frame or shell.
• The pin is a metal axle that the sheave turns on. It runs from cheek to cheek through the middle of the sheave.
Figure 6-3.-Parts of a tackle.
• The becket is a metal loop formed at one or both ends of a block; the standing part of the line is fastened to the becket.
• The straps inner and outer) hold the block together and support the pin on which the sheaves rotate.
• The shallow is the opening in the block through which the line passes.
• The breech is the part of the block opposite the swallow.
• To overhaul means to lengthen a tackle by pulling the two blocks apart.
• To round in means to bring the blocks of a tackle toward each other, usually without a load on the tackle (opposite of overhaul).
• The term two blocked means that both blocks of a tackle are as close together as they can go. You may also hear this term called block and block.