What is parallelism in GD?

In GD, Parallelism can refer to either Surface Parallelism or Axis Parallelism. Surface Parallelism is a tolerance that controls Parallelism between two surfaces or other features.

What is the difference between GD and geometric control?

If it leads to a surface, the surface is under geometric control. If it marks a diametric dimension, then GD controls the axis. This arrow may not be present in some cases. The first compartment (starting from the left) contains the geometric characteristic symbol.

How do you measure parallelism?

Refer to the Tolerance Zone diagrams above and you can tell pretty quickly how to sweep to measure Parallelism. Most of the time it’s easy just to place the datum on a surface plate and sweep the top with an indicator at constant height to measure Parallelism. GD Table of Contents GD Symbols

What is the difference between +/- tolerances and GD?

Another difference between standard +/- tolerances and GD is the shape of the tolerance zone. In conventional tolerances with a +/- tolerance in two right-angle dimensions (two dimensions to a hole for instance), the tolerance zone is rectangular shaped.

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What is parallelism tolerance in CAD?

In mechanical part drawings, parallelism tolerance allows the designer to specify the degree to which a feature ‘s orientation may vary with respect to its referenced datum by creating a tolerance zone parallel to that datum. The relevant feature, axis, or center plane must then lie within this zone.

Is parallelism a bad practice?

The short answer is yes, that is a bad practice. To explore this in more detail, we will first consider the… by GD Basics on December 20, 2014. Parallelism is a fairly common symbol that describes a parallel orientation of one referenced feature to a datum surface or line…

What is the difference between parallelism tolerance and parallelism axis?

When we apply it to a surface, it controls the parallelism between two planes. Whereas when we apply it to an axis, it controls the parallelelism of an axis is w.r.t. the reference plane. Parallelism Tolerance creates a tolerance zone of two parallel planes parallel to the datum feature or surface.