Thread

basic introduction of thread and types of thread.

1. FORMS OF THREADS NAME: KEMKAR JAIMIN AJITKUMAR EN. NO.: 160123119014 CLASS AND BATCH: 4 TH – D2 SUB. & CODE: MACHINE DESIGN & INDUSTRIAL DRAFTING (2141907) GUIDED BY: PROF. A.R. MAJITHIYA

2. CONTENTS Definition of thread Classification of threads Specification of a screw thread FORMS OF THREADS

3. THREADS A thread (screw thread) is helical ridge formed on uniform section round the curved surface. The shape of the normal section of the thread depends upon the shape of the tool which produces its groove. Classifications of threads: According to the surface on which the threads are cut External threads Internal threads According to the direction of rotation of the threaded cylinder w.r.t. engagement Right hand threads Left hand threads According to number of starts Single start threads Multi start threads

4. SPECIFICATION OF A SCREW THREAD: Shape of forms of threads Pitch Size (diameter) Length Number of starts Material Direction of threads Internal or external threads

5. These threads are found on bolts and screwed fastenings for special purposes. The British standard threads with fine pitches (B.S.F.) are used where great strength at the root is required. The British standard pipe (B.S.P.) threads with fine pitches are used for steel and iron pipes and tubes carrying fluids . BRITISH STANDARD WITHWORTH (B. S. W.) THREADS: FORMS OF THREADS:

6. British association (B.A.) thread This is a B.S.W. Thread with fine pitches. These threads are used for instruments and other precision works. American national standard thread The flat crest can withstand more rough usage than sharp V -threads. These threads are used for general purposes e.g . on bolts, nuts, screws and tapped holes.

7. Unified standard thread 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 . The thread has rounded crests and roots Square thread . The square threads, because of their high efficiency, are widely used for transmission of power in either direction . Such type of threads are usually found on the feed mechanisms of machine tools, valves, spindles, screw jacks etc .

8. Acme thread It is a modification of square thread. It is much stronger than square thread and can be easily produced. These threads are frequently used on screw cutting lathes, brass valves, cocks and bench vices . Knuckle thread It has rounded top and bottom. It can be cast or rolled easily and can not economically be made on a machine . They are usually found on railway carriage couplings, hydrants, necks of glass bottles and large molded insulators used in electrical trade .

9. Buttress thread It is used for transmission of power in one direction only . The force is transmitted almost parallel to the axis . It has a low frictional resistance characteristics of the square thread and have the same strength as that of V-thread . The spindles of bench vices are usually provided with buttress thread .

10. Metric thread It is an Indian standard thread and is similar to B.S.W. threads . It has an included angle of 60° instead of 55 °.

11. references TEXTS: R.S. khurmi Wikipedia Mechanical measurement and metrology IMAGES: R.S. khurmi

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