In Fig. 14.18 the difference in magnitude between dimensions X and Y (whether diameters or widths) divided by the length between them defines a ratio known as a taper.
For example, the conical taper in Fig. 14.19
and may be expressed as rate of taper 0.25:1 on diameter.
The ISO recommended symbol for taper is and this symbol can be shown on drawings accompanying the rate of taper, i.e. 0.25:1 The arrow indicates the direction of taper.
When a taper is required as a datum, it is enclosed in a box as follows:
3 the diameter or width at the smaller end;
4 the length of the tapered feature;
5 the diameter or width at a particular cross-section, which may lie within or outside the feature concerned;
6 the locating dimension from the datum to the cross-section referred to above.
Care must be taken to ensure that no more dimensions are quoted on the drawing than are necessary. If reference dimensions are given to improve communications, then they must be shown in brackets, e.g. (1:5 taper).
Figure 14.20 gives four examples of the methods used to specify the size, form, and position of tapered features.
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