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Planar Datum Features
Constrain 3 Degrees of Freedom
(in accordance with the ASME
Y14.5-2009 standard)
PDF of This Tip
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. The next several monthly 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.
Planar Datum
Feature
Where a planar feature is identified as a datum
feature, the practical simulator is a high quality
plane such as a surface plate which contacts the
high points of the feature. This simulator
establishes a datum plane which constrains 1
translational and 2 rotational degrees of freedom.
The video for this Tip is from Don’s
new computer based training course on GD&T
Fundamentals available on DVD and the internet in
March 2010. |
