Can a datum feature reference itself?

Can a datum feature reference itself?

RE: Can a Datum feature reference itself in Y14. You could give each dimension (width and length) its own positional tolerance. No difference. Completely legal, just not common.

How do you reference a datum?

A typical datum reference frame is made up of three planes. For example, the three planes could be one “face side” and two “datum edges”. These three planes are marked A, B and C, where A is the face side, B is the first datum edge, and C is the second datum edge. In this case, the datum reference frame is A/B/C.

How do you find datums in a drawing?

Datum Symbol On Drawings We can place the datum symbol either on the surface or on one extension line from the surface. For any surface other than a round cylinder, the datum is strictly on the side where the symbol is shown. However, for a round cylinder, the datum is the entire round surface.

What requires a Datum Reference?

A datum feature is usually an important functional surface where all other dimensions need to be in spec with reference to it. 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.

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

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. During measurement, the datum feature will contact the simulated datum which in this case is a surface plate.

What is datum feature symbol?

Datums are indicated using the following symbols (datum symbols). Datum symbols use either a white or black triangle. The letters indicating the datums are always oriented to the direction the reader looks at the drawing. The position of the datum symbol on the drawing is also relevant to the target area.

What is a Datum Reference system?

A geodetic datum or reference frame is an abstract coordinate system with a reference surface (such as sea level) that serves to provide known locations to begin surveys and create maps.

What is primary datum in GD?

A datum is a plane, a straight line, or a point that is used as a reference when processing a material or measuring the dimensions of a target. ISO Definition.

What is a datum point on a drawing?

A datum is a plane, a straight line, or a point that is used as a reference when processing a material or measuring the dimensions of a target. ISO Definition. Types of Datums. Drawing Indications of Datum Features.

What is a datum point?

A datum is a plane, a straight line, or a point that is used as a reference when processing a material or measuring the dimensions of a target. ISO Definition. Types of Datums.

What is the symbol for a datum?

Datum symbols use either a white or black triangle. The letters indicating the datums are always oriented to the direction the reader looks at the drawing. The position of the datum symbol on the drawing is also relevant to the target area.

What should be considered when selecting a datum?

When selecting Datums, designers should consider the following characteristics: Datums are important and care must be taken when selecting them. They must be easily identifiable on the part. When parts are symmetrical or have identical features that make identification of Datum Features difficult, the Datum Features should be physically identified.

What is the 3-2-1 rule for tertiary datum features?

– The tertiary datum feature has at least one point of contact with its datum plane. The 3-2-1 rule only applies to planer datum features. One may specify a datum feature that is at an angle other than 90 degrees relative to other datum features. These are called Inclined Datum Features.

How many points of contact does a secondary datum have?

– The primary datum feature has at least 3 points of contact with its datum plane. – The secondary datum feature has at least 2 points of contact with its datum plane. – The tertiary datum feature has at least one point of contact with its datum plane. The 3-2-1 rule only applies to planer datum features.

Why are reference frames important in GD & T?

A Datum Reference Frame is a coordinate system, and preferably it is a Cartesian coordinate system. Coordinate systems are valuable because they’re used to locate objects. In GD they are used to orient and locate tolerance zones.