datum system

[SAEEDGH]

hi.
I read ISO 5459-i have a problem with datum systems.
In the picture below, why resulting datum or datum system converted to play and included line while datums are two line? is there any principle for convert actual datum to datum system?

In the picture below, also there is same process to convert datum to datum system. can anyone help me?

 

[Burunduk]

The datum system is established with a close connection to the rotation and translation constraints by the datum references.

In the first picture, the primary datum feature establishes an axis from which other features will be located, and it also orients the datum system initially. Then the plane is added to represent the clocking direction (stop of last rotation) by datum feature B.

In the second picture, plane C (primary) establishes the initial orientation, then datum feature A (secondary) establishes a locating point, and the tertiary datum feature B gives a line on the mentioned plane, through the mentioned point, representing the direction in which the final lock of rotation (around the point) takes place.

 

[rimag]

Hi,

In ISO, a complete datum system that locks all six degrees of freedom consist of a plane (3 points), a line (2 points, and a point. Much like how an alignment would be in a CMM with spatial alignment, planar alignment and origin.

In your first ISO example, there is only primary and secondary reference. As described below of your example from ISO 5459:2011, the resulting datum system is the associated center line of the first cylinder and a plane that includes the axis of both cylinders.

In ISO 5459:2011, Annex C provides several examples of resulting datum systems consisting of a axis, plane, (and point if applicable).