Introductory physics books list the six simple "machines" that are the building blocks for more sophisticated devices. Of the six, arguably, the screw offers the most elegant combination of form and function, as the thread seamlessly transforms rotary motion to linear motion...and vice versa. Throughout the mechanical world, screws provide precise positioning and motion control. Heavy machinery, for example, makes wide use of ballscrews, worms and feedscrews. The external threads of such heavy-duty screws can be produced by a variety of methods, including single-point threading, thread chasing, threadmilling, hobbing and thread rolling. One efficient way to quickly make a large, precise OD thread is thread whirling. (Small and internal threads are thread-whirling candidates too; see sidebars.)
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