The previewed Datum Feature Symbol consists
of the frame, triangle, and leader connecting to the frame
. … When you select the extension line of a linear dimension, the datum feature triangle is attached to the extension line at the point where the dimension line touches the extension line.
What is a datum feature 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 are 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. … During measurement, the datum feature will contact the simulated datum which in this case is a surface plate.
What is a datum feature simulator?
Datum feature simulator: “A surface of an adequately precise form (such as a surface plate, a gauge surface, or a mandrel) contacting the datum feature(s) and used to establish the simulated datums.” … Datum feature simulators
represent the datum feature engaging surfaces of manufacturing and gauging fixtures
.
How do you select the datum features?
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.
How do you define datum?
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
.
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.
What is difference between datum and 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 datum in design?
Datum: A datum is
a form which ties together or anchors all other elements of the design
. It can be a line, like a road with houses arranged along its length, a flat plane, or even a 3D space. Many buildings all share a plane which acts as a clear datum— it’s the ground on which they are built!
Why datum is used in GD&T?
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.
Are datums perfect?
Datums are
theoretically perfect points, lines, and planes
. Datums exist within a structure of three mutually perpendicular intersecting planes known as a datum reference frame.
What is feature of size?
In GD&T the term feature-of-size (FOS) refers
to any surface, or set of parallel surfaces associated with a size dimension
. Specific examples of features of size include: A hole diameter (a cylindrical surface) Plate thickness (two opposed parallel surfaces)
What is regardless of feature size?
RFS Regardless of Feature Size is the default condition of all geometric tolerances by rule #2 of GD&T and requires no callout. Regardless of feature size simply means that
whatever GD&T callout you make, is controlled independently of the size dimension of the part
.
What is the primary datum?
Datums are theoretically perfect points, lines, and planes. … In order to properly place an imperfect, rectangular part in a datum reference frame, the primary datum feature
sits flat on one of the planes of the datum reference frame with a minimum of three points of contact that are not in a straight line
.
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.
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.
