{"id":11583,"date":"2021-11-16T17:34:01","date_gmt":"2021-11-16T15:34:01","guid":{"rendered":"https:\/\/fractory.com\/?p=11583"},"modified":"2024-01-26T14:12:25","modified_gmt":"2024-01-26T12:12:25","slug":"perpendicularity-gdt-explained","status":"publish","type":"post","link":"https:\/\/fractory.com\/perpendicularity-gdt-explained\/","title":{"rendered":"Perpendicularity (GD&T) Explained"},"content":{"rendered":"
There are 14 types of geometric tolerances in GD&T<\/a> according to ASME Y14.5-2009<\/a>. These 14 tolerances can be categorized into five main groups: form, profile, orientation, location and runout.<\/p>\n Perpendicularity is a type of orientation control. Orientation controls define the orientation of a feature with reference to a datum plane or axis. Angularity and parallelism<\/a> are other callouts in orientation control besides perpendicularity.<\/p>\n This article will explain the various aspects of perpendicularity and its two types in detail.<\/p>\n Exact perpendicularity between features is very difficult to achieve. The perpendicularity callout establishes limits within which a feature must lie to be accepted as reasonably perpendicular.<\/strong><\/p>\n Similar to GD&T straightness<\/a>, there are two ways in which perpendicularity may be applied. It can control the perpendicularity of a surface or an axis. Let us explore each type.<\/p>\n Surface perpendicularity is a 2-dimensional GD&T callout that controls the perpendicularity between two surfaces. The surfaces must be perpendicular within the tolerance limits specified in the feature control frame. Surface perpendicularity does not directly control the angle between the surfaces<\/strong>. Instead, it ensures perpendicularity by defining the location where the surface must lie for approval<\/strong>.<\/p>\n Axis perpendicularity is a 3D tolerance that specifies a cylindrical boundary where the axis of the referenced feature must lie<\/strong>.<\/p>\n As with all other GD&T callouts, the perpendicularity callout sets up a tolerance zone at the ideal location of the feature. The zone particulars, however, are different for surface and axis perpendicularity.<\/p>\n Let us see how these two zones work and the differences between them.<\/p>\n As it is apparent from the shape, the zone does not directly control the angle between the two surfaces. Instead, it creates a zone perpendicular to the datum surface and maintains the flatness of the perpendicular surface.<\/p>\n Since the zone is cylindrical, the feature control frame contains a diameter symbol to denote it.<\/p>\n The perpendicularity callout symbol bears some similarities to other commonly used GD&T callouts. This section covers some of those callouts.<\/p>\n Similar to flatness<\/a>, surface perpendicularity measures surface variation between two parallel planes<\/strong>. But unlike perpendicularity, flatness (like all other form controls) applies to a surface without a datum.<\/p>\n Another difference is that perpendicularity controls the angle<\/strong> (90\u00b0 with respect to the datum feature) while flatness does not<\/strong>. Flatness is only concerned with the smoothness of a surface and the angular variation from the desired range does not make any difference.<\/p>\n All orientation controls are similar to each other in a way. Perpendicularity is a specialized form of angularity<\/a>, as is parallelism<\/strong>. While angularity can maintain orientation at any specific angle, parallelism and perpendicularity are set at 0\u00b0\/180\u00b0 and 90\u00b0 respectively.<\/p>\n What Is Perpendicularity?<\/h2>\n
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Surface Perpendicularity<\/h3>\n
Axis perpendicularity<\/h3>\n
\nAxis perpendicularity ensures that the axis of a feature is within the perpendicularity limits in the feature control frame (FCF). The feature may be positive such as a pin, or negative such as a hole.<\/p>\nPerpendicularity Tolerance Zone<\/h2>\n
Surface perpendicularity tolerance zone<\/h3>\n
\nThe tolerance zone for surface perpendicularity is made of two parallel planes. The surface under inspection must lie in between the two planes for approval. The feature control frame controls the spacing between the two planes\u2014the smaller the spacing, the tighter the zone.<\/p>\nAxis perpendicularity tolerance zone<\/h3>\n
For axis perpendicularity, the tolerance zone is cylindrical. The zone is created around a theoretical axis that is perfectly perpendicular to the datum feature. All the points on the feature\u2019s actual axis must lie within the zone for approval.<\/p>\n
Perpendicularity vs Other Callouts<\/h2>\n
Perpendicularity vs Flatness<\/h3>\n
Perpendicularity vs Angularity<\/h3>\n
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