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,
surface quality, and
- sound fitting.
Vee-threads are either metric or inch-measure screw threads
Figure 1. Different flank angles in
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