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Saturday, 7 June 2014

Forms of Screw Threads

Forms of Screw Threads Points : Forms of Screw Threads, British Standard Whit worth (B.S.W.) Thread, American National Standard Thread, Square Thread, Acme Thread, Knuckle Thread, Buttress Thread, Unified Standard Thread, Metric Thread, British Association (B.A.) Thread The following are the various forms of screw threads.
1. British Standard Whit worth (B.S.W.) Thread
2. American National Standard Thread
3. Square Thread
4. Acme Thread
5. Knuckle Thread
6. Buttress Thread
7. Unified Standard Thread
8. Metric Thread
9. British Association (B.A.) Thread
1. British Standard Whit worth (B.S.W.) Thread It is a British standard thread outline with has common pitches. It is a equal V-thread in which angle among the flankes, calculated in an axial plane is 55°. This thread is creating on bolts with screwed fastenings for particular reason. British standard threads by fine pitches (B.S.F.) are use where great force at root is necessary. These threads are too use for line tuning and where the linked parts are subjected to enlarged vibrations as in aero with automobile work. 2. American National Standard Thread American national standard or Seller's thread has level top with roots. Flat crest can endure extra rough custom than sharp V-threads. This thread are use for common reason e.g. on nuts, screws bolts, with tapped holes. 3. Square Thread Square threads, as of their elevated competence, are extensively use for transmission of power in any direction. Such kind of threads is generally found on feed mechanism of machine tools, spindles, valves, screw jacks etc. Square threads are not as tough as V-threads but they offer less frictional conflict to motion than Whitworth threads. Pitch of square thread is frequently taken two times that of a B.S.W. thread of equal diameter. 4. Acme Thread This is an alteration of square thread. It is greatly stronger than square thread with can be simply formed. These threads are commonly use on screw cutting lathes, brass valves, cocks with bench vices. When use in conjunction by a split nut, as on lead screw of lathe, the tapered sides of thread make easy prepared engagement and disengagement of halves of nut while required. 5. Knuckle Thread This thread is also a modification of square thread and has rounded top with bottom. It can be cast or rolled simply and cannot inexpensively be prepared on a machine. These threads are use for rough and ready work. They are generally found on hydrants, railway carriage couplings, necks of glass bottles with large moulded insulators use in electrical operate. 6. Buttress Thread This is use for transmission of power in one way just. Force is conveying about parallel to the axis. This thread units the benefit of both square with V-threads it has a low frictional opposition characteristics of square thread with have similar strength as of V-thread. Spindles of bench vices are generally give by buttress thread. 7. Unified Standard Thread The three countries i.e., Great Britain, Canada and United States came to an agreement for a common screw thread system with the included angle of 60°, in order to facilitate the exchange of machinery. 8. Metric Thread This is an Indian standard thread with is like to B.S.W. threads. It has an included angle of 60° instead of 55°. 9. British Association (B.A.) Thread This is a B.S.W. thread by well pitches. These threads are use for instruments with other accuracy works.

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