Abstract： ASME Y14.5.1:2019 pdf download.Mathematical Definition of Dimensioning and Tolerancing Principles. As surface flaws may cause these center points to form a discontinuous line or plane. evaluation of actual local size requires constructing a...

ASME Y14.5.1:2019 pdf download.Mathematical Definition of Dimensioning and Tolerancing Principles.

As surface flaws may cause these center points to form a discontinuous line or plane. evaluation of actual local size requires

constructing a tangent-continuous line or plane. Examples of non-unique center points or a tangent. discontinuous center line are

shown In Figure 2-4. Because of these properties of the derived median line and plane, a local size spine is used that approximates the derived median line or plane, but Is tangent-continuous.

NOTE: The local size spine can be thought of as a well-behaved derived median line or plane, possibly obtained through some

smoothing of the denved median line or plane constructed using thi ASME Y14.S definition.

When straightness of the derived median line is evaluated (see para. 5.4.1.1), the nominally circular cross sections obtaIned from cylindrical features of size are evaluated to find the centers. In the absence of other specification, these centers will he the

center of a mating clrcle In that cross section, i.e.. an inscribed circle for an internal feature, and a circumscribed circle for an external feature.

2.3.3.2 EvaLuation of ActuaL LocaL Size (Opposed Points). If actual local size Is to be evaluated by the opposed points method, an actual local size exists:

— for every line perpendicular to the two-dimensional local size spine at the point this line Intersects the spine (parallel plane features of size);

- for every line passing through the one-dimensional local size spine in any cross section perpendicular to the spine (cylindrical features of size); or

— for every line passing through the center point (spherical features of size).

These lines are referred to as evaluation lines. See Figure 2-5 for a graphical representation of actual local sizes on a

cylindrical feature.

(a) Definition. The actual local size for a particular evaluation line is the Euclidean distance between the opposed points where

the evaluation line Intersects the actual feature. If there are more than two intersecting points, no size exists for this

evaluation line.

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