Three orientation tolerances are used when dimensioning machined parts:
- Perpendicularity, and
These tolerances establish the orientation of features to each other. These tolerances and their symbols are identified
in table below.
a) Parallelism (symbolized by two parallel lines slanting slightly to the right) is a condition of a surface or axis
where all the points on a surface are equidistant to a given datum surface and within a specified tolerance. Figure 1a
illustrates the parallelism symbol followed by its interpretation, figure 1b.
Fig. 1a Parallelism symbol on a drawing.
Fig. 1b Parallelism interpretation.
The tolerance zone is established parallel to the datum plane “D”. Parallelism tolerance, when applied to a plane
surface, establishes flatness.
b) Perpendicularity is symbolized by an upside down “T” and requires that all points on a specified feature form
a 90° angle with the datum plane or axis. Figure 2a illustrates the perpendicularity symbol followed by its
interpretation, figure 2b.
Fig. 2a Perpendicularity symbol on a drawing.
Fig. 2b Perpendicularity symbol interpretation.
In this example, the surface must lie between two parallel planes 0.005 apart. These two planes form a 90° with the
datum plane F. The tolerance zone is 0.005 as shown in figure 2.
c) Angularity is symbolized by a small angle opening to the right as demonstrated in figure 3a.
requires that all points specified on a feature form an angle with a datum reference. This tolerance is similar to
perpendicularity only the angle measures something other than 90°. In figure 3b, the surface must lie between two
parallel planes 0.02 apart. These two planes are inclined at 35° to datum plane C.
Fig. 3a Angularity symbol on a drawing.
Fig. 3b Angularity interpretation.
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