Thread Notation 6b29u

Coordinate Dimensioning and Tolerancing 0.08 M A

C

8X

7.9 - 8.1 0.14 M

0.06 A

9.6 9.4

A C M

M42 X 1.5 - 6g 0.1 M B M

8X 45°

86

6.6 6.1

20.00 - 20.13 0.14

A C

Unit

B

44.60 44.45

9.6 9.4 25.5 25.4

31.8 31.6 0.1

B

36 34

Engineering Graphics Principles A

41.3 41.1

0.02

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57.6 56.6 100 99

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0.08 M A C

ENGINEERING GRAPHICS

8X

7.9 - 8.1

0.06 A

9.6 9.4

0.14 M

A C M

M42 X 1.5 - 6g 0.1 M B M

8X 45°

86

6.6 6.1

COORDINATE DIMENSIONING and TOLERANCING Basic Thread Notation 20.00 - 20.13 0.14

A C

B

44.60 44.45

9.6 9.4

25.5 25.4

31.8 31.6

0.1

B

36 34

A

57.6 56.6

41.3 41.1

100 99

0.02

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REPRESENTING AND DIMENSIONING SCREW THREADS

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Dimensioning Symbols Basic Dimensioning Guidelines and Rules Representing and Dimensioning Screw Threads

Simplified Form

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Screw threads are depicted in one of the following three ways: (1) The simplified version, which is most commonly used—especially in industries where manual drafting is still done,

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Dimensioning Symbols Basic Dimensioning Guidelines and Rules Representing and Dimensioning Screw Threads

Simplified Form

Screw threads are depicted in one of the following three ways: (1) The simplified version, which is most commonly used—especially in industries where manual drafting is still done, (2) the schematic version which is also popular, and used frequently in industry,

Schematic Form

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Dimensioning Symbols Basic Dimensioning Guidelines and Rules Representing and Dimensioning Screw Threads

Simplified Form

Schematic Form

Screw threads are depicted in one of the following three ways: (1) The simplified version, which is most commonly used—especially in industries where manual drafting is still done, (2) the schematic version which is also popular, and used frequently in industry, and (3) the detailed method which is least often used because of the time to construct, and the fact that leftand right-hand threads are drawn in a reversed angle format.

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Dimensioning Symbols Basic Dimensioning Guidelines and Rules Dimensioning Screw Threads

.500 - 13UNC - 2A

Thread Forms Acme UN - Unified National UNR – Unified National Round

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Thread Series C – Coarse F – Fine EF – Extra Fine

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Screw threads are dimensioned according to the standards ANSI Y14.6 and ANSI Y14.6aM (Metric). For standard screw threads called out on mechanical drawings, the major diameter is identified, followed by the number of threads per inch and the thread form, series, and class of fit. The end of the screw threads is chamfered at a 45º angle unless specified otherwise. An external thread is designated by the ‘A’ following the class of fit, whereas an internal thread is classified as a ‘B’ thread (A partial thread table is displayed on the next slide). Glossary

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American National Standard, Unified, and American National Screw Threads (Partial Table) Coarsea Nominal Diameter 0 (.060) 1 (.073) 2 (.086) 3 (.099) 4 (.112) 5 (.125) 6 (.138) 8 (.164) 10 (.190) 12 (.216) 1/4 5/16 3/8 7/16 1/2 9/16 5/8 11/16 3/4 13/16 7/8 15/16 1 aClasses

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Finea

Extra Fineb

NC and UNC Thds. per inch

NF and UNF Thds per inch

NEF and UNEF Thds per inch

… 64 56 48 40 40 32 32 24 24 20 18 16 14 13 12 11 … 10 … 9 … 8

80 72 64 56 48 44 40 36 32 28 28 24 24 20 20 18 18 … 16 … 14 … 12

… … … … … … … … … 32 32 32 32 28 28 24 24 24 20 20 20 20 20

1A, 2A, 3A, 1B, 2B, 3B, 2, and 3

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bClasses

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Dimensioning Symbols Basic Dimensioning Guidelines and Rules Dimensioning Screw Threads Perfect screw threads cannot be formed up snug against a perpendicular shoulder, such as the under side of a bolt head. If the bolt is intended to advance into the receiving tapped hole all the way to the head, the last two or three threads are often removed, or relieved, to avoid a conflict with imperfect threads. .400 X .2

2X R.02 MAX

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Dimensioning Symbols Basic Dimensioning Guidelines and Rules Dimensioning Internal Screw Threads An internal thread is usually called out in the circular view of the tapped hole. The minor diameter of the thread is represented by a solid object line, whereas the major diameter of the thread is represented by a hidden line. The dimension leader line is always radial and attaches to the solid line. .375 - 24UNF - 2B

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Dimensioning Symbols Dimensioning internal screw threads requires that the major diameter of the thread—in this specific case ¼ inch—be identified with a decimal dimension (.250), number of threads per inch (20), thread form and series (Unified National Course—UNC), and the class of fit (2). The ―B‖ specifies an internal thread. 4X .250 - 20UNC - 2B

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Dimensioning Symbols Basic Dimensioning Guidelines and Rules Dimensioning Left-hand Screw Threads Left-hand threads are called out by placing the letters LH following the standard thread callout. Right-hand threads are assumed unless otherwise specified.

.250 - 20UNC - 2A LH

Socket Head Cap Screw

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Dimensioning Symbols Basic Dimensioning Guidelines and Rules Dimensioning Left-hand Screw Threads This is an example of a left-hand thread callout for a tapped hole. , righthand threads are assumed unless otherwise specified. The feature is an internal, lefthand Unified screw thread, with a .250 major diameter, 20 threads per inch, and Unified National Course series. The ―2‖ represents the class of fit, and the ―B‖ indicates that it is an internal thread.

.250 - 20UNC - 2B LH

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Dimensioning Symbols Basic Dimensioning Guidelines and Rules Dimensioning Metric Screw Threads This is an example of a metric thread callout for a tapped hole. The tolerance grade (6H) is assumed on metric specifications unless otherwise specified, so it could be removed without consequence in this example. Metric thread form Major diameter of thread (Basic)

4X M10 X 1.5 – 6H Tolerance grade – internal thread Pitch

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Dimensioning Symbols Basic Dimensioning Guidelines and Rules Dimensioning Left-hand Metric Screw Threads In this case, a metric thread with a nominal size of 8mm, and a pitch of 1.25, with a tolerance grade of 6g (standard commercial grade) has been specified. The tolerance grade for standard fits are frequently omitted from the drawing, and are assumed unless otherwise specified. Metric thread form Major diameter of thread

M8 X 1.25 – 6g LH Tolerance grade – external thread Pitch

Socket Head Cap Screw –(Left-hand Threads)

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Dimensioning Symbols Basic Dimensioning Guidelines and Rules Dimensioning Metric Screw Threads The cap screw depicted in this slide, has a metric thread exactly the same as the one shown in the previous slide. The tolerance grade has been omitted, but the standard (6g) would be assumed in the absence of another specification.

M8 X 1.25

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Dimensioning Symbols Basic Dimensioning Guidelines and Rules Constructing Hex Head Bolts and Hex Nuts Regardless of the ―true‖ projection of the hexagonal bolt head, or a nut fastener, the three-segment representation is always used. In the example below, the projection is true. However, in the next slide, the bolt will have been developed from a viewing station that has been revolved 90º from this one. .500 – 13 UNC – 2A

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Dimensioning Symbols Basic Dimensioning Guidelines and Rules Constructing Hex Head Bolts and Hex Nuts Even though the image is not a ―true‖ projection, it is shown correctly according to projection conventions. Hexagon bolt heads and hex nuts are always shown as though oriented with three of the sides shown (otherwise, it would appear the same as a bolt with a square head —as shown in the left view projection). .500 – 13 UNC – 2A

Incorrect Projection

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Dimensioning Symbols Basic Dimensioning Guidelines and Rules Projecting Hex Head Bolts, Hex Nuts and Jam Nuts This slide depicts the construction and projection of bolts and nuts. The same standard is followed in both the national and international standards.

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Dimensioning Symbols Basic Dimensioning Guidelines and Rules Dimensioning Knurling Knurling on an external feature, such as shown here, requires the type of knurl (diamond, in this case), pitch, and diameter before knurling.

PITCH 0.8 RAISED DIAMOND KNURL

M8 X 1.25

28 FULL KNURL 19.7 BEFORE KNURLING

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Dimensioning Symbols Basic Dimensioning Guidelines and Rules Dimensioning Knurling Knurling of an external feature for an internal press fit requires the type of knurl (straight in this case), pitch, and diameter before knurling. Where the diameter of the feature is to be controlled—for instance to accommodate a press fit—the diameter after knurling must also be specified. PITCH 0.8 STRAIGHT KNURL 20 MIN AFTER KNURLING

M8 X 1.25

12.5 FULL KNURL 19.7 BEFORE KNURLING

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End of Unit Number Four

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