Machine Drawing

Surface Roughness 247

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If it is necessary to indicate the sampling length, it should be selected from the series

given in ISO/R 468 and be stated adjacent to the symbol, as shown in Fig. 16.4d. If it is necessary

to control the direction of lay, it is specified by a symbol added to the surface roughness symbol,

as shown in Fig. 16.4e.

NOTE The direction of lay is the direction of the predominant surface pattern, ordinar-

ily determined by the production method employed.

Table 16.3 shows the symbols which specify the common directions of lay.

Table 16.3 Symbols specifying the directions of lay

Symbol Interpretation

Parallel to the plane of projection

of the view in which the symbol is

used

Perpendicular to the plane of

projection of the view in which the

symbol is used

Crossed in two slant directions

relative to the plane of projection

of the view in which the symbol is

used

Multi-directional

Approximately circular, relative to

the centre of the surface to which

the symbol is applied

Approximately radial, relative to

the centre of the surface to which

the symbol is applied

M

C

R

= ^ X M C R

Direction of

lay

T

Direction of

lay

X

Direction of

lay