CHAPTER 2 MEASURING TOOLS AND TECHNIQUES

CHAPTER 2 MEASURING TOOLS AND TECHNIQUES When performing maintenance and repair tasks on catapults and arresting gear equipment, you must take accurate measurements during inspection, to determine the amount of wear or service life remaining on a particular item or to make sure replacement parts used to repair equipment meet established specifications. The accuracy of these measurements, often affecting the performance and failure rates of the concerned equipment, depends on the measuring tool you use and your ability to use it correctly. COMMON MEASURING TOOLS LEARNING OBJECTIVES: Identify the different types of measuring tools. Describe the uses of different types of measuring tools. Describe the proper care of measuring tools. You will use many different types of measuring tools in the daily performance of your duties. Where exact measurements are required, use a micrometer caliper (mike). If you use the micrometer caliper properly, it will allow you to measure within one ten-thousandth (0.0001) of an inch accuracy. On the other hand, where accuracy is not extremely critical, a common straightedge rule or tape rule will suffice for most measurements. RULES AND TAPES Figure 2-1 illustrates some of the commonly used straightedge and tape rules. Of all measuring tools, the simplest and most common is the steel or wooden straightedge rule. This rule is usually 6 or 12 inches long, although other lengths are available. Steel rules may be flexible or nonflexible, but the thinner the rule is, the easier it is to measure accurately with it, because the division marks are closer to the work to be measured. Generally, a rule has four sets of graduated division marks, one on each edge of each side of the rule. The longest lines represent the inch marks. On one edge, each inch is divided into 8 equal spaces, so each space represents 1/8 inch. The other edge of this side is divided into sixteenths. The 1/4-inch and 1/2-inch marks are commonly made longer than the smaller division marks to facilitate counting, but the graduations are not normally numbered individually, as they are sufficiently far apart to be counted without difficulty. The opposite side of the rule is similarly divided into 32 and 64 spaces per inch, and it is common practice to number every fourth division for easier reading. There are many variations of the common rule. Sometimes the graduations are on one side only, sometimes a set of graduations is added across one end for measuring in narrow spaces, and sometimes only the first inch is divided into 64ths, with the remaining inches divided into 32nds and 16ths. Steel tapes are made from 6 to about 300 feet in length. The shorter lengths are frequently made with a curved cross section so that they are flexible enough to roll up, but remain rigid when extended. Long, flat tapes require support over their full length when measuring, or the natural sag will cause an error in reading. MEASURING PROCEDURES To take a measurement with a common rule, hold the rule with its edge on the surface of the object being measured. This will eliminate parallax and other errors that might result because of the thickness of the rule. Read the measurement at the graduation that coincides with the distance to be measured, and state it as being so 2-1 Figure 2-1.—Some common types of rules.