Turning Threads

In this section, we are about to discover how to machine threads with our lathe, but before jumping directly into the turning command that allows us to machine threads, we need to recap thread theory and check our thread specifications.

As you may recall, our example part features a thread starting from the front face. The first thing we will do is check the thread specifications. The thread we have to machine is an M42x4.5, a standard ISO thread with a coarse pitch.

All ISO screw threads are ruled by the following diagram:

Figure 5.13: ISO thread

Now that we can check the thread drawing, we can explain the parameters we can spot inside the diagram:

• P: This is the thread pitch. For a coarse M42, the pitch is 4.5 mm.
• Dmax: This is the screw’s maximum outer diameter. For an M42, this value must be between 41.937 mm and 41.437 mm.
• H: This is the thread height measured between sharp corners:

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