## B

a = 2D parameter 1

b = 2D parameter 2

c = 2D parameter 3

d = process e = lay pattern f = allowance x = not al lowed

Figure 6.15 The position of additional information to be added to the 'tick' symbol positions a, b and c. If only one single SF parameter is to be specified, then the numerical value and the transmission band and SL are to be indicated in the complete graphical symbol at position a. The transmission band or SL is to be followed by an oblique stroke followed by the surface parameter designation, followed by its numerical value. If a second surface parameter is to be specified it should be located at position b. If a third is required it will be located at position c. If a fourth is required the graphical symbol is enlarged in the vertical direction to make room for more lines.

■ Position 'd' - at this position the manufacturing method, treatment, coating or other requirement is located, e.g. turned, ground, plated, etc.

■ Position V - at this position information concerning the lay and orientation is given. A symbol represents the lay pattern. There are seven lay classes represented by the symbols: ' = , ±, X, M, C, R and P'. These are shown in the table in Figure 6.16.

■ Position 'f - at this position the required machining allowance is indicated as a numerical value in millimetres. The machining allowance is generally indicated only in those cases where more than one processing stage is shown on one drawing. Machining allowances are therefore found, for example, in drawings of raw, cast or forged workpieces. ■ Position V - no SF indications are to be added above the tick symbol at position x. This may seem a peculiar thing to say but in previous standards, only the Ra value was to be placed at this position, all other parameters were to be placed at a different position. This implied that the Ra value had a prominence over other parameters and that it was the most important parameter of all.

The full designation attached to positions a, b and c of a tick symbol could contain up to seven elements. Consider the following as an example:

 Graphical Symbol Interpretation Lay Pattern — 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. X Crossed in two oblique directions relative to the plane of projection of the view in which the symbol is used. m M Multi-directional. n C Approximately circular relative to the centre of the surface to which the symbol applies. # R Approximately radial relative to the centre of the surface to which the symbol applies. # P Lay is particulate, non-directional or protuberant.

Figure 6.16 Symbols for surface lay according to ISO 1302:2001

Figure 6.16 Symbols for surface lay according to ISO 1302:2001

The interpretation of this is as follows. The first specification, the 'U', means the upper specification limit that applies to the parameter Rz in the second SL (Rz2). In this instant there is no lower value and the Rz parameter in theory could be 0. If there is a lower limit then the capital letter 'L' is shown. If neither 'U' nor 'L' is shown, it is assumed to be the upper limit (U). The second specification, shown as 'X' in the above is the filter (see Section 6.2.2 above). It should be noted that a range of something like 12 filter standards will be published as Technical Specifications (ISO 16610) in 2002 and 2003. The third and fourth specifications are the transmission band limits, shown in this case as 0,08-0,8. These are the short wave and long wave filters. The fifth specification is the 2D parameter itself, in this case the Rz value in the second SL. The sixth specification in the above is the '16% rule' or the 'max-rule', in this case the 'max-rule'. The seventh specification is the parameter limit value, in this case 3,3um (Rz2).

Figure 6.17 shows examples of the use of the tick symbol. The interpretation shown in Figure 6.17a is as follows. The process is not specified therefore any which meets the roughness specification is acceptable. The parameters specified apply to the roughness 