1 / 32

Threads and Threading

Threads and Threading. Types. 1. Translation threads. square acme buttress. 2. American National thread form. WWII - US military equipment did not interchange with equipment made in Britain and Canada. 3. Unified thread form. After WWII countries agreed on need for interchangeability

jamesweaver
Télécharger la présentation

Threads and Threading

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Threads and Threading

  2. Types

  3. 1. Translation threads • square • acme • buttress

  4. 2. American National thread form • WWII - US military equipment did not interchange with equipment made in Britain and Canada

  5. 3. Unified thread form • After WWII countries agreed on need for interchangeability • Essentially the same as the American National thread form except Unified has a rounded root and either a rounded or flat crest • Is interchangeable with the American National thread form • Has 60 deg thread angle • Two major thread series - UNC and UNF

  6. 4. Metric threads

  7. 5. Right hand vs. left hand

  8. Screw thread Nomenclature (external)

  9. Major Dia: largest dia

  10. Minor Dia: smallest dia

  11. Pitch Dia: imaginary point where width of groove and thread are equal

  12. Root: bottom surface connecting 2 sides of a thread

  13. Crest: top

  14. Pitch: linear distance from corresponding points on a thread

  15. Depth: Distance from crest to root perpendicular to axis of thread on one side

  16. Flank: Sides of a thread that connect crest to root

  17. Helix Angle • Distance of movement compared to each revolution • The Lead of the helix

  18. Lead: Distance of 1 revolution (lead = pitch on a single lead thread)

  19. Thread angle: included angle between flanks of thread

  20. Unified Screw thread designation (5 components)

  21. 1/2-13-UNC-2A • 1/2 = major dia • 13 = threads per inch • UNC = Unified National Course • 2 = Class of fit • A = External Thread form (B = internal)

  22. Classes of fit • Class 1 - largest mfg tolerances, used for ease of assembly • Class 2 - used on largest percentage of threaded fasteners • Class 3 - smallest mfg tolerances, threads will be tight when assembled

  23. Methods of manufacturing threads • taps and dies • lathe • milling • grinding - used when material cannot be machined • rolling - most common

  24. Thread measuring instruments-regardless of method, pitch dia is always measured or compared • 1. mating part - simplest, no measurement involved • 2. comparator micrometer - does not measure pitch, only compares to a known standard • 3. thread micrometer - each micrometer measures a range of TPI • (8 - 13), (14 - 20), (22 - 30), (32 - 40)

  25. Measuring instruments (cont.) • 4. three wire system (most accurate) • 5. go / no go thread gages - used in production where quick gaging is necessary • 6. optical comparator - light beam shows a profile of the thread for checking thread form, helix angle, and depth (external threads)

  26. Taps and Dies • Taps - create internal threads • Dies - create external threads • Usually made of high speed steel

  27. Standard set consists of: • Taper tap - used for starting a tapped thread square with the hole • Plug tap - most common • Bottoming tap - to produce threads almost to the bottom of a blind hole

  28. Types of taps: • interrupted thread taps - used for tough materials - alternate teeth reduce friction • spiral pointed (gun) - chips are forced ahead of the tap • spiral fluted - helical flutes to draw chips out of the tap • thread forming taps - fluteless taps that do not cut, they displace the material to form the threads - ductile materials • Tapered pipe taps

  29. Tapping procedures • by hand with a tap wrench • by machine

  30. Drilling the proper hole diameter • tap drill size • selected from a chart • hole should be reamed before tapping • Tapping problems (Table B-3)

  31. Types of dies • Round split adjustable or (button) - allow for small adjustments in size • 2 piece split die. - blanks are placed in cap with guide

  32. Hand threading procedures • always start the die on the leading (throat) side • use lathe, drill press, or mill to start the die squarely • use lubricant • chamfer the end of the rod • reverse the die (or tap) after each full turn to clear chips

More Related