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.

• See User-Defined Datums for more information.

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.

• See User-Defined Datums for more information.