![]() ![]() In the case of axis perpendicularity, a cylindrical tolerance zone must be indicated. This is the case for surface perpendicularity. If no symbols are present for the zone’s shape, total wide tolerance zone is considered as the default. The feature tolerance block contains information about the shape and size of the tolerance zone and any material condition modifiers in that order. Perpendicularity symbol is ⊥ and it is used for both surface and axis perpendicularity. The geometric characteristic block houses the GD&T symbol for the geometrical tolerance. To understand the FCF better, we shall divide it into its constituent blocks as follows. This section will explain the FCF for perpendicularity in both cases. Compared to an axis, there are some minor differences when perpendicularity is applied to a surface. The leader arrow of the FCF points to the feature under control or its extension line. The feature control frame (FCF) for perpendicularity is pretty straightforward. While angularity can maintain orientation at any specific angle, parallelism and perpendicularity are set at 0°/180° and 90° respectively. Perpendicularity is a specialized form of angularity, as is parallelism. Perpendicularity vs AngularityĪll orientation controls are similar to each other in a way. Flatness is only concerned with the smoothness of a surface and the angular variation from the desired range does not make any difference. But unlike perpendicularity, flatness (like all other form controls) applies to a surface without a datum.Īnother difference is that perpendicularity controls the angle (90° with respect to the datum feature) while flatness does not. ![]() Similar to flatness, surface perpendicularity measures surface variation between two parallel planes. This section covers some of those callouts. The perpendicularity callout symbol bears some similarities to other commonly used GD&T callouts. Since the zone is cylindrical, the feature control frame contains a diameter symbol to denote it. All the points on the feature’s actual axis must lie within the zone for approval. The zone is created around a theoretical axis that is perfectly perpendicular to the datum feature. Axis perpendicularity tolerance zoneįor axis perpendicularity, the tolerance zone is cylindrical. Instead, it creates a zone perpendicular to the datum surface and maintains the flatness of the perpendicular surface. The feature control frame controls the spacing between the two planes-the smaller the spacing, the tighter the zone.Īs it is apparent from the shape, the zone does not directly control the angle between the two surfaces. The surface under inspection must lie in between the two planes for approval. The tolerance zone for surface perpendicularity is made of two parallel planes. Let us see how these two zones work and the differences between them. The zone particulars, however, are different for surface and axis perpendicularity. Perpendicularity Tolerance ZoneĪs with all other GD&T callouts, the perpendicularity callout sets up a tolerance zone at the ideal location of the feature. The feature may be positive such as a pin, or negative such as a hole.Īxis perpendicularity is a 3D tolerance that specifies a cylindrical boundary where the axis of the referenced feature must lie. Axis perpendicularityĪxis perpendicularity ensures that the axis of a feature is within the perpendicularity limits in the feature control frame (FCF). Instead, it ensures perpendicularity by defining the location where the surface must lie for approval. Surface perpendicularity does not directly control the angle between the surfaces. The surfaces must be perpendicular within the tolerance limits specified in the feature control frame. Surface perpendicularity is a 2-dimensional GD&T callout that controls the perpendicularity between two surfaces. ![]() ![]() It can control the perpendicularity of a surface or an axis. Similar to GD&T straightness, there are two ways in which perpendicularity may be applied. The perpendicularity callout establishes limits within which a feature must lie to be accepted as reasonably perpendicular. VII Bonus Tolerance in Perpendicularity What Is Perpendicularity?Įxact perpendicularity between features is very difficult to achieve.
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