{"id":13289,"date":"2022-03-25T08:56:59","date_gmt":"2022-03-25T06:56:59","guid":{"rendered":"https:\/\/fractory.com\/?p=13289"},"modified":"2024-01-26T13:51:31","modified_gmt":"2024-01-26T11:51:31","slug":"parallelism-gdt-explained","status":"publish","type":"post","link":"https:\/\/fractory.com\/parallelism-gdt-explained\/","title":{"rendered":"Parallelism (GD&T) Explained"},"content":{"rendered":"

ASME Y14.5-2009 divides tolerances in GD&T<\/a> into 14 different types. Each tolerance controls the characteristics of features to guarantee near-perfect fabrication and assembly of machine components<\/a>. These 14 tolerances are sorted into five groups based on the characteristics they control. These groups are form, profile, orientation, location and runout.<\/p>\n

Under orientation control, we have parallelism, perpendicularity and angularity tolerances. These tolerances control the orientation of a feature (such as a line, axis or surface) in respect to another reference feature (datum element).<\/p>\n

In this article, we will explain the concept of parallelism GD&T tolerance. We will also go over its tolerance zone, feature control frame and measurement methods.<\/p>\n

What Is Parallelism in GD&T?<\/h2>\n

Parallelism is a 3D GD&T orientation tolerance which maintains that two part features are parallel to each other.<\/strong> You can use it to control centerlines, center planes, cylindrical and planar surfaces parallel to the datum elements.<\/p>\n

There are two types of parallelism in GD&T<\/strong>. It may either refer to surface parallelism or axis parallelism<\/strong> depending on whether you use it to control a surface or an axis. The use of surface parallelism is more common than axis parallelism.<\/p>\n

With both types of GD&T parallelism, the goal is to maintain parallelism (0\u00b0 alignment) with the datum element (axis or plane) according to the limits specified in the feature control frame.<\/p>\n

Parallelism Tolerance Zone<\/h2>\n

\"surface
\nIn the case of surface parallelism, the parallelism tolerance zone is made of two theoretically exact parallel planes. The distance between the two planes is the tolerance limit for the callout. All the points on the planar surface or center plane must lie within the two parallel planes for a part to be approved.\u00a0<\/p>\n

It is evident from the shape of the zone that the parallelism tolerance doesn\u2019t create an angular tolerance zone to control the 0\u00b0 alignment between the controlled surface and the datum plane.<\/p>\n

Instead, it fixes the tolerance zone at a basic (or exact) 0\u00b0 angle and the permissible variation is controlled by widening or tightening the two surfaces of the zone. The greater the distance between the zone’s two planes, the more error it can accommodate.<\/p>\n

Axis parallelism creates a cylindrical tolerance zone. It is used to maintain the axis of a feature of size such as cylindrical pins or holes parallel to a datum. All the points of the feature\u2019s center axis must lie in this cylindrical zone for a part to be in spec. In this type of zone, the permissible angular deviation can be controlled by reducing or increasing the diameter of the cylindrical zone.<\/p>\n

It is worth mentioning here that the parallelism callout cannot control the location of the tolerance zone. It is only concerned with orientation. The tolerance zone exists at the location of the surface.<\/p>\n

\n
\n Scale Your Manufacturing from Prototyping to Series<\/span>\n\n