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

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 a datum feature simulator?

A datum feature simulator is the manufacturing or inspection equipment contacting the datum feature of the part. Datum feature simulators are used to establish the simulated datums. A simulated datum is a point, axis or plane established from the actual surface of the datum feature simulator. ASME Y14.5M Definitions.

What is a datum system?

A datum system is a group of datums created by combining more than one individual datum in order to use it as a reference for toleranced features.

What is a Datum Reference Frame?

A datum reference frame is a coordinate system against which the geometric dimensions and tolerances of a part are defined. The main function of the datum reference frame is to specify a foundation for the inspection of the part. It is the common coordinate system of all tolerance zones.

What is an example of a datum?

An example of a datum is the assumed altitude of a specific piece of land used as the basis in calculating the altitude of the top of a mountain on the land. A point, line, or surface used as a reference, as in surveying, mapping, or geology.

How do you identify a datum?

On a surface If it is on one side of a rectangular object like a box, the datum surface is only the side where the symbol is shown. However if the part is round like a cylinder, the datum would be the entire surface of the cylinder.

What are the types of datum?

There are two main datums in the United States. Horizontal datums measure positions (latitude and longitude) on the surface of the Earth, while vertical datums are used to measure land elevations and water depths.

Why do we use a datum?

A datum is a point, line, or surface from which dimensions are taken. It is the place to start. The datum can be a single point eg the centre of a hole or face of a feature to a component. A datum is used to reduce errors when marking out, and measuring by reducing the accumulation of errors.

What is a datum target symbol?

The datum target symbol is a circle which is divided into two parts. The lower contains datum letter and target number. For the datum target area symbols, the information about the area shape and size can be putted in the upper.

What is the use of datum target in GD?

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.

Can a centerline be a datum?

So a centerline cannot be a datum. To sum up, a datum can indeed be a centerline, but it is never to be labeled as such on a drawing.

How are datum target lines represented on a drawing?

A datum target line is represented by a target point symbol on the edge of the part in the top view of the drawing and by a phantom line on the front view, datum target C1. Since datum target C1 is on the far side of the part, a dashed radial line is used to connect the datum target symbol.

What are the GD symbols?

GD Symbols

• True Position. Position is one of the most useful and most complex of all the symbols in GD.
• Regardless of Feature Size.
• Least Material Condition (LMC)
• Maximum Material Condition (MMC)
• Datums in GD.
• Perpendicularity.
• Total Runout.
• Flatness.

What information is placed in the lower half of the datum target symbol?

The lower half is for a letter and a digit. The letter represents the datum feature, and the digit represents the datum target number. The upper half is for additional information, such as dimensions of the datum target area.

How do datum targets work?

A datum target is a point, line, or limited zone on a target with which machines and instruments for processing, measuring, and inspection come into contact in order to establish a datum.

What does it mean when the leader line to a datum target is dashed?

If you select Far-Side, the leader appears as a dashed line indicating that the datum target symbol is applied to the far hidden side of the surface where the datum target symbol is attached.

How many points of contact minimum are required for primary datum plane?

3 points

How do you establish a datum point?

Creating a datum point by projecting a point onto a face. Select a point on the model and an edge or datum axis on which to project the point. Abaqus/CAE creates the datum point where the edge or datum axis intersects a line that is normal to it and passing through the selected point, as shown in Figure 7.

What is the primary datum?

When referenced in the predominant datum reference frame, the primary datum feature constrains the location and orientation of the part. If the datum feature is not sufficiently large, the constraint on the orientation of the part may not be sufficiently stable or repeatable.

How do you create a good datum?

How do we select a datum? The primary datum needs to have at least three points of contact on the surface, which restricts three degrees of freedom. translation motion in Y and rotation about X and Z directions. The secondary datum plane should have two points of contact, which restricts two degrees of freedom.