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. 1-49).
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 alter the plug tap has already been used. Both the taper and plug taps should precede the use of the bottoming hand tap.
Pipe taps are used for pipe fittings and other places where extremely tight fits are necessary. The tap diameter, from end to end of 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 non-chamfered portion does the cutting.
Dies are made in several different shapes and are of the solid or adjustable type. The square pipe die (fig. 1-50) 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 re-threading die (fig. 1-50) is used principally for dressing over bruised or rusty threads on screws or bolts. It is available in a variety of sizes for re-threading American Standard Coarse and Fine threads. These dies are usually hexagon in shape and can be turned with a socket,box, open-end,or any wrench that will fit. Re-threading dies are available in sets of 6, 10, 14, and 28 assorted sizes in a case.
Round split adjustable dies (fig. 1-51) are called "Button" dies and can be used in either hand diestocks or machine holders. The adjustment in the screw adjusting type is made by a fine-pitch screw which forces the sides of the die apart or allows them to spring together. The adjustment in the open adjusting types is made by means of three screws in the holder, one for expanding and two for compressing the dies. Round split adjustable dies are available in a variety of sizes to cut American Standard Coarse and Fine threads, special form threads, and the standard sizes of threads that are used in Britain and other European countries. For hand threading, these dies are held in diestocks (fig. 1-52). One type die stock has three pointed screws that will hold round dies of any construction, although it is made specifically for open adjusting-type dies.
Two piece collet dies (fig. 1-51) are used with a collet cap (fig. 1-52) and collet guide. The die halves are placed in the cap slot and are held in place by the guide which screws into the underside of the cap. The die is adjusted by means of setscrews at both ends of the internal slot. This type of adjustable die is issued in various sizes to cover the cutting range of American Standard Coarse and Fine and special form threads. Diestocks to hold the dies come in three different sizes.
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