1. Purpose and importance of thread cutting by dies and taps

Threads are disconnectable, solid connections of machine parts. Where the parts are held against one another such threads are called fastening threads, i.e. vee-threads. Similarly, where the parts are set in motion towards each other they are known as travelling threads, i.e. acme threads (in the leadscrew of the lathe).

The two threads each consist of a couple of parts, namely an internal thread and an external thread. The mode of operation is determined by shape, diameter and pitch of the thread. Thread cutting is a sort of chip removal and can be undertaken by mean of a die, tap or lathe. Thread cutting by dies and taps is very easy and serves to manufacture vee-threads which, in turn, are perfectly adequate for moat fastening threads regarding:

- dimensional accuracy,
- forming,
- top surface quality, and
- sound fitting.

Vee-threads are either metric or inch-measure screw threads (Whitworth threads)

Figure 1. Different flank angles in vee-threads

1 metric thread, 2 Whitworth thread

Figure 2. Thread increase

1 metric thread (thread increase in mm), 2 inch thread (thread increase = ¼ inch = 4 turns = 1 inch), 3 thread increase, 4 = one inch

What are the differences between a metric thread and a Whitworth thread?
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