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The greatest disadvantage is the difficulty in machining such a thread. The single-point cutting tools or taps and dies used to cut the thread cannot have efficient rake and relief angles (because of the square form), which makes the cutting slow and difficult. Square threads also cannot carry as much load as a trapezoidal thread, because the ...
A perfectly sharp 60° V-thread will have a depth of thread ("height" from root to crest) equal to 0.866 of the pitch. This fact is intrinsic to the geometry of an equilateral triangle — a direct result of the basic trigonometric functions. It is independent of measurement units (inch vs mm). However, UTS and ISO threads are not sharp threads.
In manufacturing, threading is the process of creating a screw thread.More screw threads are produced each year than any other machine element. [1] There are many methods of generating threads, including subtractive methods (many kinds of thread cutting and grinding, as detailed below); deformative or transformative methods (rolling and forming; molding and casting); additive methods (such as ...
For a 3 ⁄ 8-16 tap, the above formula would produce 5 ⁄ 16, which is the correct tap drill diameter. The above formula ultimately results in an approximate 75% thread. Since metric threads specify the pitch directly, the correct tap drill diameter for metric-sized taps is computed with: =
The thread form is slightly modified to increase the minor diameter, and thus the strength of screws and taps. The major diameter still extends to within 1 / 8 H of the theoretical sharp V, but the total depth of the thread is reduced 4% from 5 / 8 H = 5 / 8 cos(30°) P ≈ 0.541P to 0.52P. [5]
Whitworth's new standard specified a 55° thread angle and a thread depth of 0.640327p and a radius of 0.137329p, where p is the pitch. The thread pitch increases with diameter in steps specified on a chart. The Whitworth thread system was later to be adopted as a British Standard to become British Standard Whitworth (BSW).
The major minus pitch technique also works for inch-based threads, but you must first calculate the pitch by converting the fraction of threads-per-inch (TPI) into a decimal. For example, a screw with a pitch of 1/20 in (20 threads per inch) has a pitch of 0.050 in and a 1 ⁄ 13 in pitch (13 threads per inch) has a pitch of 0.077 in.
The thread depth is 0.54125 × pitch. The outermost 1 ⁄ 8 and the innermost 1 ⁄ 4 of the height H of the V-shape are cut off from the profile. The relationship between the height H and the pitch P is found using the following equation where θ is half the included angle of the thread, in this case 30°: [ 3 ]