Quick Answer: What Is The Difference Between A Datum And A Datum Feature?

What is 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..

Does flatness required datum?

Flatness is a condition of a specified surface having all elements in one plane. Flatness tolerance provides a tolerance zone of specified and defined by two parallel planes in where the specified surface must lie. Flatness is applied to an individual surface, flatness tolerance does not need to be related to a datum.

What is profile surface?

Profile of a surface describes a 3-Dimensional tolerance zone around a surface, usually which is an advanced curve or shape. … Profile controls all the points along the surface within a tolerance range that directly mimics the designed profile.

What is the flatness symbol?

GD&T Flatness is a common symbol that references how flat a surface is regardless of any other datum’s or features. It comes in useful if a feature is to be defined on a drawing that needs to be uniformly flat without tightening any other dimensions on the drawing.

What is an example of a datum?

Datum definitions An example of a datum is a new scientific discovery used to reach a conclusion about the common cold. 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.

What is a datum used for?

An engineering datum used in geometric dimensioning and tolerancing is a feature on an object used to create a reference system for measurement. In engineering and drafting, a datum is a reference point, surface, or axis on an object against which measurements are made.

What is a datum line?

Noun. datum line (plural datum lines) (engineering) A line which serves as a reference or base for the measurement of other quantities.

What is profile in GD&T?

In GD&T, profile tolerance defines a uniform boundary around a surface within which the elements of the surface must lie. Profile is a complex tolerance that simultaneously controls a feature’s form, size, orientation, and sometimes location. … An example of profile tolerance is shown below.

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. This is important to note when marking out a job. … A datum is used to reduce errors when marking out, and measuring by reducing the accumulation of errors.

What is a datum target symbol?

Symbol Description Datum targets are circular frames divided in two parts by a horizontal line. The lower half is for a letter and a digit. The letter represents the datum feature, and the digit represents the datum target number.

What is a datum height?

The datum surface is that which passes through mean sea level at the 30 tide gauges and through points at zero AHD height vertically below the other basic junction points.

What are GD&T symbols?

Geometric Dimensioning and Tolerancing (GD&T) is a system for defining and communicating engineering tolerances. It uses a symbolic language on engineering drawings and computer-generated three-dimensional solid models that explicitly describe nominal geometry and its allowable variation.

What is datum dimensioning?

A datum dimension is a group design object. It allows for the dimensioning of a linear distance of a collection of objects, relative to a single reference object. The first object chosen is the ‘base’.

Can a profile be a datum?

Profile can control, form, location, orientation, and size or any subset of these. Profile can be used with or without datum references and with or without basic dimensions.

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.

How is profile of a line calculated?

Gauging / Measurement: Profile of a line is measured using a gauge that is referenced to the true profile at the given specific cross-section. Because there are an infinite amount of 2D cross-sections of any part, the number or locations of measurement points can be specified on the drawing.

How do I choose a datum point?

Creating a datum point by selecting two end points. Select two edges on the model; and enter the distance from the datum point to each edge, as shown in Figure 4. For detailed instructions, see Creating a datum point at a specified distance from two edges.