How do you define datum targets?

How do you define datum targets?

A datum target is described using a circular frame with a horizontal line drawn through the middle (datum target frame). In the bottom half of the datum target frame, you write the letter/symbol indicating the same datum as that of the entire feature, along with the number of the datum target.

When should datum targets be used?

In GD, a datum target may be used to specify a point, line, or area on a part to establish a datum. This is sometimes necessary when a part feature is too large or naturally irregular to create a datum. Parts that are cast, forged, or molded often benefit from the use of datum targets.

How many datum targets are there?

A primary datum plane is established by a minimum of three datum targets not in a straight line. 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.

Can datum targets be on different planes?

The establishment of a primary common datum plane is defined by a total of 3 datum targets on two different parallel offset datum plane features. However, this process is not explicated in ISO and the establishing process cannot function with only 3 datum targets on different planes mathematically.

What is the difference between a datum target and a datum feature?

The datum is an imaginary but theoretically perfect surface, line, or points. A datum feature, on the other hand, is the physical representation of datum. Datum targets are specified regions of the datum feature used for locating the part in a fixture.

What is a moveable datum target?

Movable datum targets are datum targets that are not fixed at their basic location, are free to translate, and can apply to a point, line, or area.

Can a datum be curved?

10.1 allows the use of curved surface as datum under ” mathematically defined surface concept. It says the theoretically true geometric counterpart of the shape is used to establish the datum.

What is the 3 2 1 rule of identifying datum planes using datum targets?

The 3-2-1 rule defines the minimum number of points of contact required for a part datum feature with its primary, secondary, and tertiary datum planes. It only applies when all three plaines are used. The 3-2-1 rule says: – The primary datum feature has at least 3 points of contact with its datum plane.

Are datums perfect?

A Datum is a perfect point, line, plane or surface but only exists theoretically. However a Datum Feature is a tangible surface, point or axis on a part where that theoretical datum is located. The reason they are not equal to each other is because the part surface is never 100% perfect.

What does a movable datum target symbol indicate?

The Movable Datum Target symbol indicates that a datum target is not fixed at its basic location and is free to translate.

What is the difference between a datum and a datum feature?

Datums and datum features. A datum feature is a part feature (or FOS), that contacts a datum during measurement. A datum is a theoretically exact plane (or axis or center-plane), from which dimensional measurement should be made. The measurements that refer to this datum will be made from the surface plate.

Can datum a be a surface?

A Datum is a perfect point, line, plane or surface but only exists theoretically. However a Datum Feature is a tangible surface, point or axis on a part where that theoretical datum is located.