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Introduction to Geometric Dimensioning and Tolerancing

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Advantages

Allows designer to describe the design intent.

  • Considers how the part should be shaped in order to function a certain way.

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Advantages

GD&T is Absolutely Succinct. There is no extra information, and everything has a precise meaning.

Trying to convey the same information with notes would be extremely difficult.

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Advantages

It is a graphical language, can be used internationally.

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Advantages

Since the tolerances can refer to specific geometric qualities, it allows for wider tolerances that are easier to attain.

Here are two examples...

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Hole Position

Consider the following:

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Think about the tolerance zone

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Think about the tolerance zone

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How much can the center be away from target?

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hmmmm....

GD&T will let us create a tolerance zone that is round. That will allow us to use a more generous tolerance.

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Table Example

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Table Example

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Using GD&T To Control Flatness Separately from Height

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Tolerance Zones

Can be shaped like (perfect)

Cylinders

Tubes

Spheres

Flat disks

Ribbons

Flat Plates

Contoured “Skins”

Need to be located exactly

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Datums

Datums describe how the tolerance zone is to be located in an exact way.

The top surface of the block must be parallel to the blue datum surface to within the geometric tolerance.

The size tolerance is shown in green.