Geometric Dimensioning and Tolerancing

Don’t throw away money during dimensional inspection.

Are you scrapping valuable product because it fails dimensional inspection? If you’re not using Geometric Dimensioning and Tolerancing (GD&T), you may be scrapping usable parts without even knowing it.

GD&T is a better method of defining dimensions and tolerances because it provides a better representation of how parts are manufactured and of how they relate to one another at assembly.

For example, when conventional linear dimensions and tolerances are used to specify a hole, a square tolerance zone is defined. When the same hole is specified with GD&T, a circular tolerance zone is defined, which better represents the way the position is likely to deviate from its nominal location during fabrication.

In addition, a circular tolerance zone is the best way to describe the acceptable position of the hole with respect to a mating part. Each part that fails inspection because its hole position is outside the square tolerance zone, but inside the round GD&T tolerance zone, is a part that could be used instead of scrapped. The round GD&T tolerance zone is 57% bigger than the square tolerance zone of conventional linear tolerances!

Furthermore, you may be able to benefit from bonus tolerance, depending on your part design and application. Bonus tolerance, in the case of the hole described above, is additional tolerance that can be applied to the position of the hole when the diameter of the hole departs from its Maximum Material Condition (MMC). For a hole, MMC is when the diameter of the hole is at the minimum allowed by the tolerance. As the hole approaches Least Material Condition (LMC), the largest diameter allowed by the tolerance, the bonus tolerance increases. For a hole at nominal diameter, i.e., midway between MMC and LMC, the circular tolerance zone is actually 214% bigger than the original square tolerance zone!

How many functional parts have you rejected at inspection because you haven’t implemented GD&T?

Of course, the example provided is very rudimentary, and each design must be carefully considered to properly apply GD&T principles. Your existing part drawings can be updated to include appropriate geometric dimensions and tolerances, or your existing GD&T drawings can be reviewed for accuracy.

Contact MechanicalDesigner.com today to learn how GD&T can save you money and improve the efficiency of your manufacturing operations!