Machinery's Handbook, 31st Edition
2120 Historical and Miscellaneous Threads Briggs Pipe Thread.— The Briggs pipe thread (now known as the American Standard) is used for threaded pipe joints and is the standard for this purpose in the United States. It derives its name from Robert Briggs. Casing Thread.— The standard casing thread of the American Petroleum Institute has an included angle of 60 degrees and a taper of 3 ∕ 4 inch per foot. The fourteen casing sizes listed in the 1942 revision have outside diameters ranging from 4 1 ∕ 2 to 20 inches. All sizes have 8 threads per inch. Rounded Thread Form: Threads for casing sizes up to 13 3 ∕ 8 inches, inclusive, have rounded crests and roots, and the depth, measured perpendicular to the axis of the pipe, equals 0.626 × pitch − 0.007 = 0.07125 inch. Truncated Form: Threads for the 16-and 20-inch casing sizes have flat crests and roots. The depth equals 0.760 × pitch = 0.0950 inch. This truncated form is designated in the A.P.I. Standard as a “sharp thread.” Cordeaux Thread.— The Cordeaux screw thread derives its name from John Henry Cordeaux, an English telegraph inspector who obtained a patent for this thread in 1877. This thread is used for connecting porcelain insulators with their stalks by means of a screw thread on the stalk and a corresponding thread in the insulator. The thread is approximately a Whitworth thread, 6 threads per inch, the diameters most commonly used being 5 ∕ 8 or 3 ∕ 4 inch outside diameter of thread; 5 ∕ 8 inch is almost universally used for telegraph purposes, while a limited number of 3 ∕ 4 -inch sizes are used for large insulators. Dardelet Thread.— The Dardelet patented self-locking thread is designed to resist vibra tions and remain tight without auxiliary locking devices. The locking surfaces are the tapered root of the bolt thread and the tapered crest of the nut thread. The nut is free to turn until seated tightly against a resisting surface, thus causing it to shift from the free position (indicated by dotted lines) to the locking position. The locking is due to a wedging action between the tapered crest of the nut thread and the tapered root or binding surface of the bolt thread. This self-locking thread is also applied to set screws and cap screws. The holes must, of course, be threaded with Dardelet taps. The abutment sides of the Dardelet thread carry the major part of the tensile load. The nut is unlocked simply by turning it backward with a wrench. The Dardelet thread can either be cut or rolled, using standard equipment provided with tools, taps, dies, or rolls made to suit the Dardelet thread profile. The included thread angle is 29 degrees; depth E = 0.3 P ; maximum axial movement = 0.28 P . The major internal thread diameter (standard series) equals major external thread diameter plus 0.003 inch except for 1 ∕ 4 -inch size which is plus 0.002 inch. The width of both external and internal threads at pitch line equals 0.36 P. “Drunken” Thread.— A “drunken” thread, according to prevalent usage of this expression by machinists, etc., is a thread that does not coincide with a true helix or advance uniformly. This irregularity in a taper thread may be due to the fact that in taper turning with the tailstock set over, the work does not turn with a uniform angular velocity, while the cutting tool is advancing along the work longitudinally with a uniform linear velocity. The change in the pitch and the irregularity of the thread is so small as to be imperceptible to the eye, if the taper is slight, but as the tapers increase to, say, 3 ∕ 4 inch per foot or more, the errors become more pronounced. To avoid this defect, a taper attachment should be used for taper thread cutting. Echols Thread.— Chip room is of great importance in machine taps and tapper taps where the cutting speed is high and always in one direction. The tap as well as the nut to be threaded is liable to be injured, if ample space for the chips to pass away from the cutting edges is not provided. A method of decreasing the number of cutting edges, as well as increasing the amount of chip room, is embodied in the “Echols thread,” where every alternate tooth is removed. If a tap has an even number of flutes, the removal of every other tooth in the lands will be equivalent to the removal of the teeth of a continuous thread. It is, therefore, necessary that taps provided with this thread be made with an odd number of lands, so that removing the tooth in alternate lands may result in removing every other tooth in each individual land. Machine taps are often provided with the Echols thread. French Thread (SF).— The French thread has the same form and proportions as the American Standard (formerly US Standard). This French thread is being displaced grad ually by the International Metric Thread System.
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