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# How is GD flatness calculated?

## How is GD flatness calculated?

Flatness is can be measured using a height gauge run across the surface of the part if only the reference feature is held parallel. You are trying making sure that any point along the surface does not go above or below the tolerance zone.

## How is flatness measured?

In application, one way to physically measure flatness is to use a height gage, as we can see in Figure 2. To use the height gage correctly, the part to be measured is first placed upon 3 columns with adjustable heights. Then, the height gage is run across the surface while looking at the amplitude of the needle.

How is parallelism and flatness measured?

If we want to measure the parallelism of one side (we’ll say the bottom) to the other side (the top), we can rest the bottom on a surface plate and compare one plane (or axis) to the other. The bottom face is “leveledout” the measure the flatness of the top face.

### Is flatness a feature of size?

Flatness for a feature of size (Flatness DMP) can be applied Regardless of Feature Size (RFS) or at Maximum Material Condition (MMC).

### How do you manually measure parallelism?

Move the target or height gauge straight forward to perform measurement. The difference between the largest measured value (highest height) and the smallest measured value (lowest height) is the parallelism value.

Can flatness be greater than parallelism?

Parallelism is very common in its surface form. When dealing with any flat surfaces, flatness may be called out, but parallelism is usually more critical since the relation of surfaces in an assembly is more important.

#### What is the purpose of the ASME Y14.5 standard?

The ASME Y14.5 standard establishes symbols, definitions, and rules for geometric dimensioning and tolerancing. The purpose of the standard is to ensure clear communication of detailed information throughout the design and manufacturing process for mechanical parts.

#### Which is an example of flatness in GD & T?

Flatness is a GD form tolerance that is conceptually simple. According to the ASME Y14.5 standard, it “specifies a tolerance zone defined by two parallel planes within which the surface must lie.” Figure 1. ASME GD Flatness Example

Which is the best method to evaluate flatness?

The Minimum Zone method of evaluating flatness in GD is by far the most accurate, as it is the closest to the ASME standard. Above (Figure 7), we can see that the software has created two theoretical parallel planes in green to sandwich the points as tightly as possible.

## How to check the tolerance set by flatness?

There are different ways to check if the final measurements conform to the tolerance set by flatness. The method depends on the surface, so we are going to discuss each instance separately. Flatness measurements require a surface plate and a height gauge, probe, or a surface of some type.