What Is A Datum In Engineering?

How do you define datum?

A datum is theoretical exact plane, axis or point location that GD&T or dimensional tolerances are referenced to.

All GD&T symbols except for the form tolerances (straightness, flatness, circularity and cylindricity) can use datums to help specify what geometrical control is needed on the part..

What is a datum plane?

A datum plane is a plane on the target that is established as a datum. It can be a target’s external plane (datum plane) or center plane (datum center plane). … A datum that is a theoretically exact plane. ASME Y14.5-2009. The plane of a datum feature simulator established from the datum feature.

How do I choose a Datum Reference?

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 a datum point?

In engineering and drafting, a datum is a reference point, surface, or axis on an object against which measurements are made. These are then referred to by one or more ‘datum references’ which indicate measurements that should be made with respect to the corresponding datum feature .

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 line in engineering?

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

What is the purpose of a datum?

A geodetic datum 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. In this way, datums act similar to starting points when you give someone directions.

How do I find my datum?

Finding the datum used by your map On a USGS topographic map the datum information is in the fine print at the bottom left of the map. The datum will always be NAD 27. There may be information on how many meters to shift a position to convert it to NAD 83.

Can a Datum Reference itself?

I often get the question, “How can a feature reference itself in a feature control frame?” The answer is, “It can’t.” Datum features referenced in a feature control frame are establishing a datum reference framework which serves as the origin of measurement.

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 in design?

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.