Conventions, Abbreviations and Symbols Objectives 2.11

Conventions, Abbreviations and SymbolsObjectives

1. To identify the conventional representations of common mechanical components.

2. To identify and apply the machining symbols, which indicate machined surfaces, on mechanical drawing.

3. To draw and apply welding symbols to welded joints on mechanical drawings.

4. To write out in full common engineering abbreviations.5. To apply conventional presentation and machining symbol in

the construction of bolt and nut.ConventionsIn mechanical drawings the true representation of common engineering features, such as screw threads, bearings, etc. are rarely required. These features are usually indicated by accepted conventional representation, the use of which saves much drawing time.

screw threads interrupted view flat feature on cyl parts

splines and serrations knurling springs

gears repeated features rolling bearings

External screw thread

Internal screw thread

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Conventions, Abbreviations and Symbols Objectives 2.11

Screw thread assembly

Solid and hollow shafts

Other sections

Flat feature on cylindrical parts

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Conventions, Abbreviations and Symbols Objectives 2.11

Shaft

Hub

Knurling

Compression spring

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Conventions, Abbreviations and Symbols Objectives 2.11

Tension spring

Spur gear

Engagement of spur gears

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Conventions, Abbreviations and Symbols Objectives 2.11

Repeated features

Rolling bearings

Welding symbolsWelding is a process of fusing work pieces together to form a permanent joint. The indications of welds and weld joints are specified in BS EN 22553.

Elementary welding symbols Method of indication

Position of symbols Application examples

Welding symbol is generally the representative of the shape of the weld to be made or the edge preparation to be used. A selected welding symbols from BS EN 22553 is shown below.

Type of weld Illustration Symbol

square butt weld

single-V butt weld

single-bevel butt weld

single-V butt weld with broad root face

single-bevel butt weld with broad root face

single-U butt weld (parallel or sloping sides)

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Conventions, Abbreviations and Symbols Objectives 2.11

single-J butt weld

backing run; back or backing weld

fillet weld

plug weld; plug or slot weld

spot weld

seam weld

A weld joint is indicated on a drawing by an arrow, a dual reference line consisting of two parallel lines (one continuous and one dashed), and a weld symbol. The dashed line can be drawn either above or beneath the continuous line. For symmetrical welds, the dashed line is unnecessary and should be omitted.

Additional information in the form of supplementary symbols, weld size, etc. can also be indicated above or below the reference line.Depending on tDepending on the relative positions of the actual weld, welding symbol is to be placed either above or beneath the reference line, in accordance with the following regulation:he relative positions of the actual weld, welding symbol is to be placed either above or beneath the reference line, in accordance with the following regulation:

(i) For symmetrical welds only: the dashed line is omitted.

(ii) To be welded on the arrow side: the symbol is placed on the continuous line side of the reference line if the weld (weld face) is on the arrow side of the joint.

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Conventions, Abbreviations and Symbols Objectives 2.11

(iii) To be welded on the other side: the symbol is placed on the dashed line side if the weld (weld face) is on the other side of the joint.

Type of weld Symbol Illustration Indication on drawing

Square butt weld

Single-V butt weld

Fillet weld

Plug weld

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Conventions, Abbreviations and Symbols Objectives 2.11

Spot weld

Engineering abbreviationsEngineering abbreviations are used on mechanical drawings to save space and drafting time. The following rules should be observed when using abbreviations to express the intended meaning:

   1. Abbreviations (text equivalents) shall be the same in the

singular and plural.2. Full stops shall not be used except where the abbreviation

forms a word (e.g. NO. as an abbreviation for "number").3. Capital letters are preferred.4. Only commonly used and easily understood abbreviations

should be used; others should be avoided and the intended meaning expressed in words.

Table of commonly accepted symbols and abbreviationsTerm Abbreviation

Across flats AFAssembly ASSY

Centres CRSCentre line CL

Chamfer or chamfered CHAMCheese head CH HD

Countersunk / countersink CSKCountersunk head CSK HD

Counterbore CBORECylinder or cylindrical CYL

Diameter: preceding a dimension ØDiameter: in a note DIA

Dimension DIMDrawing DRG

Equally spaced EQUI SPExternal EXT

Figure FIG.Hexagon HEX

Hexagon head HEX HDInternal INT

Left-hand LHLong LG

Machine MCMaterial MATL

Maximum MAX

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Conventions, Abbreviations and Symbols Objectives 2.11

Minimum MINNot to scale (in a note and underlined) NTS

Number NO.Pitch circle diameter PCD

Radius: preceding a dimension RRadius: in a note RAD

Reference REFRequired REQD

Right-hand RHRound head RD HD

Screw or screwed SCRSheet (referring to a drawing sheet) SHSketch (prefix to a drawing number) SK

Specification SPECSpherical diameter (only preceding a DIM) SØ

Spot face SFACESquare: preceding a dimension �

Square: in a note SQStandard STD

TaperThread THD

Thick THKTolerance TOL

Typical or typically TYPUndercut UCUT

Volume VOL

Bolt and nut Stud

A bolt has an external thread which extends along only part of its shank. The thread length equals to a little over twice the diameter of the bolt. Above the thread is the plain section which terminates in a bolt head. A bolt, secured by a nut, is used to fasten work pieces. The typical form of bolt is the ISO metric bolt.

Typical dimension of ISO metric bolt

Construction of hexagon nut

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Conventions, Abbreviations and Symbols Objectives 2.11

A stud has threads on both ends and an unthreaded shank in the middle. When using to hold work pieces, the metal end is screwed into a base, and the other end takes by a nut securing the work pieces.

Nomenclature of stud

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