Category: Uncategorized
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Datums are the key to good profile tolerances In both cases, profile tolerances only control the form of a feature. To control the feature’s orientation or location, datum features must be called out in the tolerance frame. In the examples below, all four examples would pass inspection! As the designer, you must communicate the right…
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Positional tolerances, in order to determine the location of features, theoretical exact dimensions and a control feature frame can determine the locations of any feature (points, axes, planes and median surfaces). The tolerance zone is located symmetrically about the theoretical centre. For fixing locations, always use positional tolerance.For viewing or access holes, linear dimensions may…
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Concentricity… or Co-axiality Both concentricity and co-axiality share the same control feature symbol which can cause confusion. Concentricity = 2D & Co-axiality = 3D Concentricity is a 2D tolerance zone feature around a theoretically exact centre point of the datum. Typically used to control position of one circle to another, however as form is not…
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For symmetry control, the tolerance is applied to the theoretically exact centre (axis or plane) of the datum shown in the tolerance frame. Similar to concentricity, the theoretical median plane of the slot must lie within 0.2mm tolerance zone stated, the width of the slot is treated separately. Also shown, the depth of the slot…
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It is important to note; the angle range for a specific tolerance zone can be calculated with simple trigonometry. The value ‘0.4’ stated controls the width of the tolerance zone, not the angle of the surface Perpendicular measurement of an axis to a datum surface can be measured by running a dial indicator along the…
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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