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.
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.