Reading Prints with Fasteners and Springs

1
CHAPTER 9

• Reading Prints with Fasteners and Springs

2
Learning Objectives

• Identify the ASME standard for screw thread
  representations
• Define screw thread terminology
• Read prints with screw thread representations and
  thread notes
• Read and identify the parts of metric and Unified
  and American National threads

3
Learning Objectives

• Identify fastener head types
• Read prints containing pins, rivets, washers,
  retaining rings, keys, keyways, and keyseats
• Define spring terminology and read prints with
  spring representations

4
Fasteners

• Threaded fasteners
• Keys
• Pins
• Rivets
• Weldments (Chapter 15)

5
Screw Thread Fasteners

• Hold parts together
• Level and adjust objects
• Transmit power
• Cover containers
• Unified Thread Series standardization
• Unified Inch Screw Threads
• Unified Screw Threads Metric Translation

6
Screw Threads
7
Cutting Internal Threads

• Tap drill
• Tap
• Tap set
• Taper tap
• Plug tap
• Bottoming tap

8
Cutting External Threads

• Die
• Lathe

9
Thread Forms

• Unified threads
• Most common threads for threaded fasteners
• Sharp-V threads
• Not common
• Fits and seals tightly
• American National threads
• Flat root
• Generally replaced the sharp-V threads

10
Unified Threads
11
Thread Forms

• Metric threads
• Similar to Unified thread form
• ISO standardization
• Whitworth threads
• Original British standard thread form
• Square threads
• Transmit power
• Generally replaced by Acme threads

12
Metric Threads
13
Thread Forms

• Acme threads
• Transmit power
• Screw jacks
• Vice screws
• Buttress threads
• High stress along the thread axis applications
• Dardelet threads
• Self-locking
• Resist vibrations

14
Acme Threads
15
Thread Forms

• Rolled threads
• Electric sockets
• Lamp bases
• American National Standard taper pipe threads
• Standard threads used on pipes and pipe fittings
• May provide pressure-tight joints

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American National Standard Taper Pipe Threads
17
Thread Representations

• Describe the location of a thread where used
• Detailed
• Schematic
• Simplified
• Selection based on use and purpose of the drawing

18
Thread Representations

• ASME standards
• ASME Y14.6, Screw Thread Representation
• ASME B series

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Detailed Representation

• Pictorial display
• Necessary for some applications

20
Schematic Representation

• Approximate the appearance of threads
• Distance between threads often exaggerated

21
Simplified Representation

• Most common thread symbol in industry
• Clearly describe threads
• Can be used in all situations

22
Unified and American National Thread Notes

• 1/213 UNC2A
• 1/2 major diameter in inches
• 13 number of threads per inch
• UNC thread series
• 2 class of threads
• A external thread

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Unified and American National Thread Major
Diameter

• Numbered series less than 1/4 inch
• 0 - 12
• Gage diameter from which the thread is
  manufactured

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Unified and American National Thread Series

• UNC Unified National Coarse
• UNF Unified National Fine
• UNEF Unified National Extra Fine
• UNS Unified National Special

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Unified and American National Thread Class

• Fit
• 1 large tolerance
• 2 general-purpose moderate tolerance
• 3 close tolerance

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Unified and American National Internal or
External Threads

• A external thread
• B internal thread

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Additional Specifications

• After internal or external classification
• Blank space right-hand thread
• LH left-hand thread
• After right-hand or left-hand specification
• Blank space single lead
• L2X pitch double lead
• L3X pitch triple lead

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Additional Specifications

• After lead specification
• Internal thread depth
• External thread length
• THRU internal thread through the part
• MOD thread modification

29
Metric Thread Notes

• M 10 X 1.56H
• M symbol for ISO metric threads
• 10 nominal major diameter in millimeters
• 1.5 thread pitch in millimeters
• 6 grade of tolerance
• H tolerance class

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Metric Thread Grade of Tolerance

• 3, 4, 5, 6, 7, 8, 9
• 3 through 5 fine
• 7 through 9 coarse

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Metric Thread Tolerance Class

• Internal threads
• G tight allowance
• H no allowance
• External threads
• e large allowance
• g tight allowance
• h no allowance

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Additional Metric Thread Specifications

• After tolerance class
• Blank space right-hand threads
• LH left-hand threads
• After right-hand or left-hand specification
• Internal thread depth
• External thread length
• THRU internal thread through the part

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Other Thread Form Notes

• Notes for several other threads forms
• Acme example 5/88 ACME2
• National Pipe Thread (NPT) example 3/414 NPT

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Thread Notes on a Print
35
Measuring Screw Threads

• Vernier caliper
• Micrometer
• Rule
• Scale
• Screw pitch gage

36
Bolts

• Identified by a thread note, length, and head
  type

37
Nuts

• Classified by thread specifications and type

38
Screws

• Machine screws (shown) and cap screws
• Specified by thread, length, and head type
• Set screws
• Specified by thread, length, head or headless,
  and type of point

39
Washers
40
Internal Threads on Prints

• Includes allowance for runout, or vanish, and
  room for the tool
• Displays pilot hole depth for blind holes
• Often shows a thread chamfer
• May include a counterbore for a joint with a
  shoulder

41
External Threads on a Print

• Includes allowance for runout, or vanish
• Often shows a lead-in chamfer
• May include a relief for a joint with a shoulder

42
Pipe Threads

• Pressure-tight joint, with or without a sealer
• Taper pipe threads for general use, NPT (National
  Pipe Thread)
• Dryseal pipe threads, NPTF (National Pipe Taper
  Fuel)
• Free/loose-fitting mechanical joint, not
  pressure-tight
• Fixture joints, mechanical joints with locknuts,
  hose couplings
• Rigid mechanical joint, not pressure-tight
• Structural purposes such as railings or racks

43
Pipe Threads
44
Additional Threaded Fasteners

• Lag screws
• Wood screws
• Self-tapping screws
• Screw thread inserts
• Self-clinching fasteners

45
Dowel Pins

• Used in machine fabrication
• Generally pressed into a hole

46
Taper Pins and Other Pins

• Better for part alignment and removal than
  straight dowel pins
• Hold parts together
• Lock parts
• Transmit power

47
Retaining Rings

• Generally require a groove in the shaft or
  housing
• Mounting with a special pliers tool
• Self-locking retaining rings

48
Keys, Keyways, and Keyseats
49
Rivets

• Head formed by hammering, pressing, or forging
• Classified by body diameter, length, and head
  type

50
Springs

• Mechanical spring
• Helical (shown)
• Flat

51
Common Spring Materials

• High-carbon spring steels
• Alloy spring steels
• Stainless spring steels
• Music wire
• Oil-tempered steel
• Copper-based alloys
• Nickel-based alloys

52
Basic Spring Design Criteria

• Material gage
• Kind of material
• Spring index
• Direction of the helix
• Type of ends
• Function

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Spring Terminology
54
Spring Terminology

• Compression springs
• Extension springs
• Coil
• Deflection
• Helix direction

• Free length
• Compression length
• Solid height
• Loading extension
• Pitch

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Spring Ends
56
Flat Springs
57
Additional Springs

• Torsion spring
• Helical torsion spring
• Spiral torsion spring
• Torsion bar spring
• Wave springs

• Volute spring
• Coned disk spring
• Constant force spring
• Garter spring

58
Spring Representations

• Specified in ASME Y14.13M, Mechanical Spring
  Representation
• Detailed
• Common
• Realistic representation
• Schematic
• Less common
• Easy to draw
• Clearly represent springs
• Require clearly written spring specifications

59
Spring Representations
60
Spring Representations

• Phantom lines can be used to simplify the
  drafting of repeated detail

61
Spring Specifications

• Also referred to as spring data
• Accompany the spring drawing
• Outside or inside diameter
• Wire gage
• Material
• Type of ends

• Surface finish
• Free and compressed length
• Pitch
• Number of coils
• Helix direction
• Force requirements
• Types of ends
• Torque

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Glossary

• Allowance
• The tightness of fit between the mating parts.
• Blind hole
• A hole that does not go through.
• Bolt
• A threaded fastener with a head on one end and is
  designed to hold two or more parts together with
  a nut or threaded feature.

63
Glossary

• Cap screws
• Fine-finished machine screws that are generally
  used without a nut.
• Classes of threads
• A designation of the amount of tolerance and
  allowance specified for a thread.
• Coil
• One 360revolution of the wire used to make the
  spring.

64
Glossary

• Compression length
• Also called the solid length, the maximum
  recommended design length for the spring when
  compressed.
• Compression springs
• Release their energy and return to their normal
  form when compressed.
• Coned disk spring
• Also known as the Belleville spring, a conically
  shaped spring washer for use as a compression
  spring.

65
Glossary

• Constant force spring
• Similar to a spiral torsion spring. The inner end
  is normally not fastened so it is free to rotate.
  The coils do not expand. The outer end of the
  spring can be pulled creating uniform force on
  the coil.
• Deflection
• The movement from free length to the solid length
  in a compression spring.
• Die
• A machine tool used for cutting external threads.

66
Glossary

• Dowel pins
• Metal cylindrical fasteners that retain parts in
  a fixed position or keep parts aligned.
• Extension springs
• Release their energy and return to the normal
  form when extended.
• Fit
• Identifies a range of thread tightness or
  looseness.

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Glossary

• Flat springs
• Arched or bent flat-metal shapes designed so when
  placed in machinery they cause tension on
  adjacent parts.
• Free length
• The length of the spring when there is no
  pressure or stress to affect compression or
  extension.
• Garter spring
• A long close coil extension spring with hook or
  ring ends so the ends can be joined forming a
  large loop.

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Glossary

• Helical torsion springs
• Designed to provide resistance or to exert a
  turning force in a plane at 90 to the axis of
  the coil.
• Helix direction
• Specified as right-hand or left-hand. The
  direction of the twist used to create the spring.
• Key
• An important machine element, which is used to
  provide a positive connection for transmitting
  torque between a shaft and hub, pulley, or wheels.

69
Glossary

• Keyseat
• A groove or channel cut in a shaft for
  positioning a key.
• Keyway
• A shaft and key are inserted into a hub, wheel,
  or pulley where the key mates with a groove
  called a keyway.
• L1
• A gaging member that effectively checks the
  functional conformance of the threads.

70
Glossary

• Lag screws
• Designed to attach metal to wood or wood to wood.
• Lathe
• A machine that holds a piece of material between
  two centers or in a chucking device.
• Lead
• The lateral distance a thread travels during one
  complete rotation.

71
Glossary

• Left-hand thread
• A thread that engages with a mating thread by
  rotating counterclockwise, or with a turn to the
  left when viewed toward the mating thread.
• Loading extension
• Extended distance to which an extension spring is
  designed to operate.
• Machine screws
• Thread fasteners used for general assembly of
  machine parts.

72
Glossary

• Mechanical spring
• An elastic body whose mechanical function is to
  store energy when deflected by a force and to
  return the equivalent amount of energy upon being
  released.
• Nut
• Tightened upon the bolt or the bolt head can be
  tightened into a threaded feature.
• Pitch
• One complete helical revolution, or the distance
  from a point on one coil to the same
  corresponding point on the next coil.

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Glossary

• Retaining rings
• Provide a stop or shoulder for holding bearings
  or other parts on a shaft.
• Right-hand thread
• A thread that engages with a mating thread by
  rotating clockwise, or with a turn to the right
  when viewed toward the mating thread.
• Rivet
• A metal pin with a head used to fasten two or
  more materials together.

74
Glossary

• Runout
• Circular runout of major or minor cylinders with
  respect to the pitch cylinder.
• Screw thread inserts
• Helically formed coils of diamond-shaped wire
  screwed into a threaded hole to form a mating
  internal thread for a threaded fastener.
• Screw threads
• A helix or conical spiral formed on the external
  surface of a shaft or internal surface of a
  cylindrical hole.

75
Glossary

• Self-clinching fastener
• Any device, usually threaded, that displaces the
  material around a mounting hole when pressed into
  a properly sized drilled or punched hole.
• Self-tapping screws
• Designed for use in situations where the mating
  thread is created by the fastener.
• Set screws
• Help prevent rotary motion and to transmit power
  between two parts such as a pulley and shaft.

76
Glossary

• Solid height
• The maximum compression possible.
• Spiral torsion spring
• Designed to wind up and exert force in a rotating
  direction around the spring axis.
• Spring
• A mechanical device, often in the form of a
  helical coil that yields by expansion or
  contraction due to pressure, force or stress
  applied.

77
Glossary

• Spring index
• A ratio of the average coil diameter to the wire
  diameter.
• Tap drill
• A tap drill is used to make a hole in material
  before tapping.
• Tap
• The machine tool used to form an interior thread.
  Tapping is the process of making an internal
  thread.

78
Glossary

• Thread form
• The design of a thread determined by its profile.
• Thread note
• The information that clearly and completely
  identifies the thread being used.
• Thread series
• Groups of common major diameter and pitch
  characteristics determined by the number of
  threads per inch.

79
Glossary

• Thread
• The part of a screw thread represented by one
  pitch.
• Threaded fasteners
• Thread forms manufactured into products that can
  be used for fastening two or more features or
  parts together.
• Torsion bar spring
• A straight bar or rod used to provide resistance
  to a twisting movement around a longitudinal axis.

80
Glossary

• Torsion springs
• Designed to transmit energy by a turning or
  twisting action.
• Vanish thread
• Also referred to as a partial thread, washout
  thread, or thread runout, and is that portion of
  the incomplete thread that is not fully formed at
  root or at crest and root.
• Volute spring
• A conical shaped compression spring made of
  rectangular cross section material.

81
Glossary

• Washer
• A flat, disc-shaped objects with a center hole to
  allow a fastener to pass through.
• Wave springs
• Also called flat wire compression springs,
  occupies an extremely small area for the work it
  performs.
• Weldment
• An assembly of parts welded together.
• Wood screws
• Similar in function to lag screws and are
  available in a wide variety of sizes, head
  styles, and materials.