{"id":18198,"date":"2022-07-26T18:18:45","date_gmt":"2022-07-26T15:18:45","guid":{"rendered":"https:\/\/fractory.com\/?p=18198"},"modified":"2024-01-26T13:44:53","modified_gmt":"2024-01-26T11:44:53","slug":"angularity-gdt-explained","status":"publish","type":"post","link":"https:\/\/fractory.com\/angularity-gdt-explained\/","title":{"rendered":"Angularity (GD&T) Explained"},"content":{"rendered":"

As defined per ASME Y14.5-2009, GD&T<\/a> uses 14 geometric tolerances for specific control over various part features. These controls enable the fabrication of many machine parts<\/a> with enviable accuracy.<\/p>\n

For ease of understanding, these 14 controls are divided into five main groups. These are form, profile, orientation, location and runout.<\/p>\n

The tolerances under each of the five categories primarily control the feature of the category they belong to. For instance, the tolerances under the runout category (circular and total runout<\/a>) control the part runout. But under certain circumstances, they may control other features as well.<\/p>\n

Of the five groups, orientation tolerances control the tilt associated with part features. Angularity is a type of orientation control besides parallelism and perpendicularity.<\/p>\n

In this article, we shall take a look at the angularity tolerance, its various aspects, feature control frame and measurement methods. Let us start by defining what angularity is.<\/p>\n

What Is Angularity?<\/h2>\n

Angularity is a 3-D GD&T callout that helps maintain a specified angle between a feature (line or surface) and a reference feature. It can be used to reference a line with respect to another line but more commonly it is used to maintain a surface at an angle to a datum or reference plane. This is especially important for parts with angled surfaces that mate with other parts in an assembly.<\/p>\n

At times, angularity finds use in aligning a feature of size, such as pins or holes in a surface, to the desired angle. In those cases, angularity controls the center axis of the hole to fix its orientation.<\/p>\n

Angularity is also used to control the orientation of non-circular features such as tabs and slots. The angularity callout creates a tolerance zone around the mid-plane to control these features.<\/p>\n

Angularity Tolerance Zone<\/h2>\n

\"angularity<\/p>\n

The biggest misconception regarding angularity is that it creates an angular tolerance zone such as 30 degrees +\/- 10′. This would mean that the feature is supposed to be at a 30 degrees angle in relation to a datum and is allowed an angular variation of 10 minutes on either side. But this is not the case with angularity.<\/p>\n

The shape of the tolerance zone changes with the feature being controlled. In the case of surfaces, the tolerance zone is expressed by two parallel planes that are aligned with the exact angle required by design. In other words, the zone is oriented to the datum at a basic (or theoretically exact) angle and the surface variation is allowed to float between the two planes.<\/p>\n

If the zone width increases, the degree to which an erroneous angle is accepted also increases. Thus, it is the width of the zone that is indirectly restricting the permissible variation of the angle. For such a part to be in spec, all the points on the surface must lie within the envelope.<\/p>\n

In the case of a circular feature of size, such as a cylindrical pin or a hole, the zone is expressed as a cylindrical tolerance zone around the axis of the said feature. This zone is aligned to the basic angle with respect to the datum and the diameter of the zone is specified in the feature control frame. Same as before, the zone’s diameter determines the permissible angular variation. As long as the center axis of the feature lies within the tolerance zone, the part is approved.<\/p>\n

When used to control non-circular features of size, such as tabs and slots, angularity creates a planar tolerance zone with one plane on either side of the central plane. The center of the feature at each point must lie between the two planes of the tolerance zone.<\/p>\n

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