2. Construction and types of dies and taps

Thread cutting on the external cylindrical surface is made by means of a die. The internal cylindrical surface is processed by using a tap.

Figure 3. Die with holder

1 die, 2 holder

Figure 4. Machine tap

1 tap head (with entering, plug and plug third taps), 2 tap shank, 3 square to hold the tap wrench

The die consists of a die body, chip chambers and starting taper. The rake angles are formed by the chip chambers. Chip removal is made by means of the starting tapers produced by tapered counter-borings. The remaining thread turns are used for ensuring alignment and smoothing.

Figure 5. Die arrangement

1 chip chambers, 2 starting taper, 3 chip angle, 4 die body

Figure 6. Die and tap angles

1 free angle, 2 taper angle, 3 chip angle

What is the purpose of the rake angle and which are its functions?
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The following types are distinguished:

- open dies,
- closed dies, and
- prenotched dies.

Figure 7. Types of dies

open die, closed die, prenotched die

A closed die cannot be adjusted. The die featuring a groove-like prenotching may initially be used like its closed counterpart.

If required, the web is removed by grinding and it is then used like an open die.

The open die can also be varied in diameter, that is to say either increased or decreased.

The following taps are distinguished:

- hand tap, and
- machine tap.

Cutting generally pertains to entering, plug and plug (third) taps.

In the case of manual taps, one distinguishes between

- entering tap,
- plug tap, and
- plug third tap.

Figure 8. Hand tap

entering tap
plug tap
plug third tap

Thereby, the globe-like starting taper ensures proper chip removal, the remaining thread section serves to guarantee alignment.

Figure 9. Starting taper of the hand tap

1 entering tap, 2 plug tap, 3 plug third tap, 4 starting taper, 5 internal thread

Plug and plug third taps are turned in a little by hand so that the tap fits into the prenotched thread.

In the case of machine taps (see Fig. 4) all cutting is made by only one tap with a relatively short starting taper.

Nut taps are used in order to cut the thread with one cut in short through holes or in nuts.

Figure 10. Machine internal tap

The drills combine entering, plug and plug third taps in one long starting taper.

The starting taper is five to sixfold on the thread pitch.

Figure 11. Starting taper of the machine tap

1 entering tap, 2 plug tap, 3 plug third tap

Which types of dies are known?
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Which are the principal parts of dies and taps?
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