Tag: GD&T
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Tolerance zone defined by two parallel planes offset to datum surface Both datums ‘A’ and ‘B’ are required in order to constrain the hole axis in all directions
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In this example we have used flatness to control our surface datum ‘A’. The upper surface is defined to be parallel to surface datum ‘A’ as shown in the control frame, to the value specified. Parallelism can also be used to control the relationship between hole centres. Note the use of the diameter symbol in…
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Straightness can be defined in two ways; a 2D tolerance zone bounded by two parallel lines, typically applied to an edge or surface, or a 3D tolerance zone bounded by a cylinder, when applied to an axis. A tolerance zone is defined by the maximum allowable deviation of a feature bound by the geometry stated…
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Flatness is defined by a 3D tolerance zone bounded by two parallel planes. Flatness is measured by a number of extracted points across the whole surface.
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Roundness is defined by a 2D tolerance zone bounded by two concentric circles. Roundness is measured by a number of extracted points applied around a single cross section of a cylindrical, conical or spherical surface
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Cylindricity is defined by a 3D tolerance bounded by two concentric cylinders. Unlike roundness, cylindricity is measured by a number of extracted points along a rotated surface about a common axis of a cylindrical, conical or spherical surface.
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GD&T datums control six degrees of freedom using primary (plane), secondary (line) & tertiary (point) references. Datum targets help with complex shapes.
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GD&T ensures manufacturing accuracy by using dimensional tolerances to control variations from exact dimensions.