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the illustration page and also into the eye that the reader. The valve dimensions follow the dimensioning convention laid down in the future ISO 129-1:2003 standard. Tolerances have been left off the figure for convenience. In this situation there are two datum features. The an initial is the left-hand annular confront of the biggest cylindrical diameter, i.e. The face with the 30° chamfer. Horizontal dimensions linked with this datum face use a terminator in the form of a small circle. The other datum feature is the centre rotational axis that the spool valve stood for by the chain dotted line. Every the expansion lines touch the overview of the spool valve. The measurement values are usually placed parallel come their dimension line, close to the middle, above and clear of it. Measurement values should be put in such a means that they are not crossed or be separated by any other line.

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There are number of exceptions come this as viewed in the drawing in number 4.3:

1. Measurement values the the running dimensions are shown close to the arrowheads and also not in the centre of the measurement line. This uses to the "19", "13" and also "-20" horizontal dimension, i.e. Any running measurement value.

2. Dimension values have the right to be placed above the extension of the dimension line past one the the terminators if space is limited. This is the situation with respect come the "1" horizontal measurement of the 30° chamfer.

3. Measurement values deserve to be in ~ the end of a leader line the terminates at a dimension line. This applies when over there is too small space for the dimension value come be added in the usual way between the extension lines. This is the situation with the horizontal "2" dimension for the O-ring groove ~ above the external diameter of the spool valve.

4. Dimensional values have the right to be placed above a horizontal extension to a measurement line where an are does not enable placement parallel come the dimension line. This is the situation with the "21" diameter the the O-ring groove. This dimension is additionally different in the the dimension line and also the arrowhead room in the contrary direction to the "14" and "24" diameters watched on the left that the spool valve. Furthermore, in this case, the line has actually only one terminator (the various other one is assumed).

All the above descriptions use to direct dimensions. However, part dimensions room angular and also are dimensioned in levels or radians. The dimensioning of angle is simply as essential as the dimensioning of direct dimensions if a component is to be dimensioned appropriately for manufacture. Angular dimensions usage the very same four facets as described above for direct dimensions.

In the case of the spool valve in number 4.3, two of the 14 dimensions space angles. These room the angles of the 2 chamfers. The 45° dimension has the two arrowhead terminators on the within of the measurement arc whereas the 30° dimension has the arrowhead on the external of the angular measurement arc. The last is offered because an are is limited.

All measurement values, graphical symbols and also annotations should generally be positioned such that they deserve to be read from the bottom and from the right-hand next of the drawing. These room the normal analysis directions. However, in part instances, reading from the bottom-right is not always feasible if the needs stated above are to be met. With referral to number 4.3, it is not possible to accomplish these requirements with respect to the 45° chamfer and also the 2.5 measurement value. In this cases, the reading direction is the left-hand side and the bottom the the drawing. Number 4.4 reflects the common positions of linear dimensions and angular measurement values as provided in the latest ISO standard.

Figure 4.5 mirrors three different methods the dimensioning-related features. Through parallel and also running dimensioning, the place of the feet centres and the right-hand plate leaf are related to the datum left-hand edge. The benefit of parallel and running dimensioning is that every attribute is related ago to the

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Figure 4.4 Dimensioning different angular features

Parallel dimensioning

Running dimensioning

Chain dimensioning

Figure 4.5 Parallel, running and chain dimensioning same datum. Running and parallel dimensioning are similar methods. Chain dimensioning is one entirely different dimensioning methodology. In this case, only the left-hand feet is directly related come the left-hand datum surface. The right-hand hole is only related come the datum surface in a an additional manner and also the right-hand sheet is just related come the left-hand leaf in a tertiary manner. The very name "chain" illustrates the flaw in the the dimensions space chained together and not individually related earlier to a datum.

The dimensioning convention presented in figure 4.3 is the convention given in the recent ISO 129-1:2003 standard. Previous ISO standards have used slightly different dimensioning conventions and of course it is very likely that part old illustrations will conform to this conventions. Number 4.6 mirrors a stepped obelisk which has been dimensioned in a manner i m sorry is different from the convention in figure 4.3 yet which would have actually been encourage and enabled in vault ISO standards.

With reference to figure 4.6, the size on the illustration which do not conform to the current ISO 129-1:2003 convention however which do conform to previous versions of the standard are as follows:

I

>-

" " 30

10 i 30

10 20 ^_--;-te.

10 ^_te.

Parallel dimensioning

Running dimensioning

Figure 4.5 Parallel, running and chain dimensioning o rf o

Figure 4.6 Dimensioning practice according come previous ISO standards

1. Estimate lines do not touch the outside outline that the part. There is a small space in between the component and the extension line. It makes the component stand-alone and away indigenous the dimensioning and also therefore simpler to read.

2. Dimension values may be inserted not parallel come the dimension line however perpendicular to it, e.g. The "({>30".

3. Measurement values might interrupt the measurement line, e.g. The "30" and the "35".

4. Diameters have the right to be displayed in fifty percent their complete form, e.g. The "40".

5. Dimension values deserve to be placed away indigenous the center of the dimension line and also off to one side, e.g. The "45°" and also the "2".

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6. Short dimensions making use of reversed arrows do not need to have actually a constant dimension line, e.g. The "2" width of the chamfer.