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Cones as Datum Features Constrain 3 Translations and 2 Rotations
(In accordance with the ASME Y14.5-2009 standard)

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There is a new chart in the ASME Y14.5-2009 standard that shows the degrees of freedom that are constrained when the feature is a primary datum feature and, where appropriate, applies RMB. The chart also shows the relationship between the feature type, simulator and theoretical datum(s) that are established. This series of six Tips illustrate the features shown in the chart. Although some of the simulators are illustrated as physical inspection equipment, these simulators may also be simulated by "soft gaging" optical or probing methods.

Conical Datum Feature

A conical feature (internal or external) will establish a datum axis and a datum point. The simulator is an inverse cone that contacts the high points of the conical feature. This simulator establishes an axis and a datum point at the apex of the cone. The axis constrains 4 degrees of freedom and the point constrains the translation along the axis. The axis will establish two datum planes (not shown). The point will establish a datum plane which is perpendicular to the axis and passes through the point. The only degree of freedom not constrained is rotation around the datum axis.

Back to Tips Tip added Feb 2010