Datums from Targets
Planar Datums from Targets
A datum plane may be established by datum targets in one of the following ways.
3-Point Plane
A plane established by:
3 surface point targets.
1 surface point target and 1 surface line target.
All targets must lie on a surface referenced by the feature.
The surface normal at each target must be generally consistent and nearly parallel to the normal of the related datum plane.
May only be referenced as a primary datum of a datum reference frame.
2-Point Plane
A plane established by:
2 surface point targets.
1 surface line target.
All targets must lie on a surface referenced by the feature.
The surface normal at each target must be generally consistent and nearly parallel to the normal of the related datum plane.
May only be referenced as a secondary datum of a DRF in which the primary reference is a plane. The datum plane established by the 2-point plane must be orthogonal to the primary datum plane.
1-Point Plane
A plane established by:
1 surface point target.
The target must lie on a surface referenced by the feature.
May only be referenced
As a secondary datum of a DRF in which
The primary datum is an axis. The datum plane established by the 1-point plane must be orthogonal to the primary datum axis.
The primary datum is prismatic (e.g., a pattern of holes with parallel axes). The datum plane established by the 1-point plane must be normal to the translational DOF that is not constrained by the primary datum.
As a tertiary reference in a DRF in which
The primary and secondary datums constrain all DOF except one translation. The datum plane established by the 1-point plane must be normal to the unconstrained translation. For example, in DRF A|B|C where A and B are orthogonal planes, A and B constrain all DOF except for a translation parallel to A and B. Thus, C must be a plane that is normal to that translation (and thus orthogonal to A and B).
The primary and secondary datums constrain all DOF except one rotation. The datum plane established by the 1-point plane must be parallel to the axis of the unconstrained rotational DOF. For example, in DRF A|B|C where A is an axis and B is a plane normal to A, A and B constrain all DOF except for the rotation about A. Thus, C must be a plane that is parallel to that axis (and thus parallel to A).
User-defined Plane
A datum plane whose targets are defined by the user.
No rules or restrictions.
May be used for datum planes from targets that may not be established by one of the methods described above.
Axial Datums from Targets
A datum axis may be established by datum targets in one of the following ways.
2-Center-Point Axis
An axis established by:
2 sets of 3 equally spaced surface point targets defining a circle.
2 circular surface curve targets.
3 equally spaced surface point targets defining a circle and a circular surface curve targets.
All targets must lie on a surface referenced by the feature.
The circles established by the targets must be coaxial.
May only be referenced as a primary reference in a DRF.
1-Center-Point Axis
An axis established by:
3 equally spaced surface point targets defining a circle.
A circular surface curve target.
All targets must lie on a surface referenced by the feature.
May only be referenced as a secondary reference in a DRF in which the primary reference is a plane. The datum axis established by the 1-center-point axis must be orthogonal to the primary reference plane.
User-defined Axis
A datum axis whose targets are defined by the user.
No rules or restrictions.
May be used for datum axis from targets that may not be established by one of the methods described above.