Table of Contents
How many points are required to establish a secondary datum?
Because datum feature A is primary, at least three datum target points must be defi ned. or both of them may. of the three points create the secondary datum.
What is the minimum number of points of contacts required to establish datum plane A?
Remember that a plane can be defined by at least three points. Once the part is placed on the primary datum plane, then it will be brought to contact with the second datum plane.
What is a secondary datum?
– The secondary datum feature has at least 2 points of contact with its datum plane. – The tertiary datum feature has at least one point of contact with its datum plane.
What is true position GD?
The True Position is the exact coordinate, or location defined by basic dimensions or other means that represents the nominal value. In other words, the GD “Position” Tolerance is how far your feature’s location can vary from its “True Position”.
Why is a datum point important?
A datum reference or just datum (plural: datums) is some important part of an object—such as a point, line, plane, hole, set of holes, or pair of surfaces—that serves as a reference in defining the geometry of the object and (often) in measuring aspects of the actual geometry to assess how closely they match with the …
How many points of contact does a secondary datum have?
– The primary datum feature has at least 3 points of contact with its datum plane. – The secondary datum feature has at least 2 points of contact with its datum plane. – The tertiary datum feature has at least one point of contact with its datum plane. The 3-2-1 rule only applies to planer datum features.
What is the 3-2-1 datum precedence rule?
Datum precedence rule or 3-2-1 rule. According to this rule, the minimum number of point of contacts for the primary datum as 3, the secondary datum as 2, and tertiary datum as 1. The first, second and third datum references in the feature control frames are primary, secondary and tartiary datums, respectively. Figure 5 explains the above rule.
How many datum targets are used to establish a secondary datum plane?
Two datum targets are used to establish a secondary datum plane. And one datum target establishes a tertiary datum plane. A combination of datum target points, lines, and areas may be used.
Which is the correct definition of a datum feature?
Datum Features ≠ Datums. A datum feature is usually an important functional surface where all other dimensions need to be in spec with reference to it. However, things get a little tricky when clarifying what the datum actually is. A Datum is a perfect point, line, plane or surface but only exists theoretically.