Part 2. Block-and-Tackle Rigging
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42 Block-and-Tackle Rigging Introduction Section 1.01 introduced the four main principles of rigging called the 4 Ks. In the following sections, these principles will be applied to different kinds of rigging systems. Section 2.01 looks at their application to block and tackle rigging. Begin by getting to know the system. Under this heading, the things that the rigger needs to know to use a block and tackle safely are 1. the weight of the load to be lifted 2. the weight of the block and tackle 3. the capacity of the block and tackle 4. the working-load limit (WLL) of the rope 5. the lead line pull (LLP) 6. the load capacity of the supporting member 7. the total load on the supporting member Part 2 2.01 43 Anatomy of a Block-and-Tackle System A block and tackle consists of a standing (or fled) block attached to the supporting member, a running (or fall) block attached to the load, and a line of fiber rope (see fig. 2.1). The line for a blockand -tackle system can be natural or synthetic fiber. (More detailed information on types and strength of line is given later.) The principal part of a block is the pulley, or sheave, consisting of one or more grooved wheels supported by wood or metal side plates that turn on a shaft. The block is used to change the direction of force utilized to move an object with a line. It is much easier to raise something to the grid using a block and pulling down on the line than it is to stand on the grid and pull it up. Not only is there less strain on the back but the rigger can use body weight to help raise the load. Blocks are rated for working-load limits. Each block should have a label on its side indicating the manufacturer’s name and the working-load limit. This rating indicates that all of the components of the block have been engineered to withstand the working load. Sometimes there is a code indicating the type of bearings used in the block. If the type of bearing is not evident, call the manufacturer to get a list of its codes. Do not use unrated blocks for heavy loads. If an unrated block fails while you are using it, it is your fault, and you are liable. 2.02 Fig. 2.1. Block and tackle 44 A. Wooden Blocks Figure 2.2 shows the parts of a wooden block. 1. The wooden shell (or cheeks) keeps the rope in the sheave groove. 2. The straps, made of steel, transmit the load from the pin to the hook. 3. The sheave, or pulley, is the grooved wheel over which the rope runs. 4. The pin is the axle on which the sheaves turn. The pin supports the entire weight of the load and transmits the load from the sheave to the straps. 5. The swallows is the larger opening through which the rope passes. 6. The breech is the smaller opening at the other end of the block. 7. The becket is the attachment point of the dead end of the line. 8. A thimble is used to reduce the stress on the rope at the becket. 9. A hook or shackle is used to attach the strap to a sup- porting member. B. Metal Blocks Metal blocks, figure 2.3, are similar to wooden blocks. If the metal shell (or cheeks) is strong enough, it can actually support the Fig. 2.2. Wooden block 45 pin and transmit the load from the pin to the hook, and no straps are needed. In addition, metal blocks very often have some type of improved bearing to allow the sheave to turn with less friction. C. Other Types of Blocks Other types of rigging equipment are finding their way onto the stage. Venues close to navigable bodies of water sometimes use rated marine-grade sailing pulleys for block-and-tackle rigging . The blocks are load rated and lightweight, can be furnished with good ball bearings, and are easy to handle. Due to the small sheave diameter, they work particularly well with braided synthetic line. For simple work lines, mountain-climbing rescue pulleys are easy to use. They are load rated, efficient, and lightweight. Load Distribution on a Block A. Static Load Figure 2.4a shows a single block with a load of 100 lb. on it...


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