Classification of Screw Threads – Application Of Screw threads

Classification of Screw Threads – Application Of Screw threads

Classification Of Screw Threads
Screw threads having various applications can be classified as follows

1. According to location

  • external screw thread (on bolts etc.)
  • internal screw thread (in nuts etc.)

2.According to configuration

  • straight (helical) – most common, e.g., bolts, studs etc.
  • taper (helical), e.g., in drill chuck
  • radial (scroll) as in self centering chuck

3 . According to the direction of the helix

  • right hand (common)
  • left hand (occasionally)

4. According to form

  • vee thread (600 or 550 angle) – most common
  • acme thread (290)
  • square thread (generally in power screws)
  • buttress thread (45o)
  • worm thread (290 ~ 400)
  • semicircular (groove section) thread being used in recirculating type bolts, screws.

5. According to standard

  • BSW (British Standard Whitworth); thread – size is designated by TPI (threads per inch)
  • metric thread; thread size is specified by pitch or lead (in mm)

6. According to number of start

  • single start – most common
  • multi-start (2 to 4)

7. According to spacing of threads

  • TPI (no. of threads per inch), e.g. 12 TPI
  •  pitch (or lead) – distance between two successive threads (or length of travel of the nut for one rotation of the screw), in mm

8. According to compactness or fineness of threads

  • general threads (with usually wide thread spacing), pipe threads (more densed desired)
  • fine threads (generally for leak proof)

9. According to segmentation

  • full threads (common)
  • half turns as in half nuts
  • sector thread – e.g., in the jaws of lathe chucks.

Read More: Lead Screw Mechanism -types , Advantages

Nomenclature and Terminology used In Screw Threads
Nomenclature and Terminology used In Screw Threads

General Applications Of Screw Threads

The general applications of various objects having screw threads are :
fastening : screws, nut-bolts and studs having screw threads are used for temporarily fixing one part on to another part
joining : e.g., co-axial joining of rods, tubes etc. by external and internal screw threads at their ends or separate adapters
clamping : strongly holding an object by a threaded rod, e.g., in c-clamps, vices, tailstock on lathe bed etc.
• controlled linear movement : e.g., travel of slides (tailstock barrel, compound slide, cross slide etc.) and work tables in milling machine, shaping machine, cnc machine tools and so on.
• transmission of motion and power : e.g., lead screws of machine tools
converting rotary motion to translation : rotation of the screw causing linear travel of the nut, which have wide use in machine tool kinematic systems
position control in instruments : e.g., screws enabling precision movement of the work table in microscopes etc.
precision measurement of length : e.g., the threaded spindle of micrometers and so on.
• acting as worm for obtaining slow rotation of gear or worm wheel
exerting heavy force : e.g., mechanical presses
conveying and squeezing materials : e.g., in screw conveyor, injection moulding machine, screw pump etc.
• controlled automatic feeding in mass production assembly etc.

Sachin Thorat

Sachin is a B-TECH graduate in Mechanical Engineering from a reputed Engineering college. Currently, he is working in the sheet metal industry as a designer. Additionally, he has interested in Product Design, Animation, and Project design. He also likes to write articles related to the mechanical engineering field and tries to motivate other mechanical engineering students by his innovative project ideas, design, models and videos.

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