TAPS AND DIES

You may have to make gaskets of rubber, cork, leather, or composition materials. For cutting holes in gasket materials, a hollow shank GASKET PUNCH may be used (fig. 1-50). Gasket punches come in sets of various sizes to accommodate standard bolts and studs. The cutting end is tapered to a sharp edge to produce a clean uniform hole. To use the gasket punch, place the gasket material to be cut on a piece of hard wood or lead so that the cutting edge of the punch will not be damaged. Then strike the punch with a hammer, driving it through the gasket where holes are required. REVIEW QUESTIONS Q22. Identify the different types of punches. Q23. What is a center punch used for? Q24. What is a prick punch used for? TAPS AND DIES LEARNING OBJECTIVES: Identify the different types of taps and dies. Describe the uses of different types of taps and dies. Taps and dies are used to cut threads in metal, plastics, or hard rubber. The taps are used for cutting internal threads, and the dies are used to cut external threads. There are many different types of taps. However, the most common are the taper, plug, bottoming, and pipe taps (fig. 1-53). The taper (starting) hand tap has a chamfer length of 8 to 10 threads. These taps are used when starting a tapping operation and when tapping through holes. Plug hand taps have a chamfer length of 3 to 5 threads and are designed for use after the taper tap. Bottoming hand taps are used for threading the bottom of a blind hole. They have a very short chamfer length of only 1 to 1 1/2 threads for this purpose. This tap is always used after the plug tap has been used. Both the taper and plug taps should precede the use of the bottoming hand tap. Pipe taps are used for pipefitting and other places where extremely tight fits are necessary. The tap diameter, from end to end of the threaded portion, increases at the rate of 3/4 inch per foot. All the threads on this tap do the cutting, as compared to the straight taps, where only the nonchamfered portion does the cutting. Dies are made in several different shapes and are of the solid or adjustable type. The square pipe die (fig. 1-54) will cut American Standard Pipe thread only. It comes in a variety of sizes for cutting threads on pipe with diameters of 1/8 inch to 2 inches. A rethreading die (fig. 1-54) is used principally for dressing over bruised or rusty threads on screws or bolts. It is available in a variety of sizes for rethreading American Standard Coarse and Fine threads. These dies are usually hexagon in shape and can be turned 1-34 Figure 1-53.—Types of common taps. Figure 1-54.—Types of solid dies.