# How Do You Determine Flatness Tolerance?

## Can flatness ever be applied to a feature of size?

The MMC modifier tells us us that we can gage the part with a fixed size gage.

In all cases, when flatness is applied to a feature of size, the flatness tolerance value may be smaller than, equal to, or larger than the size tolerance value..

## What instrument measures flatness?

Height Gauge Using a dial indicator holder, a lever-type dial gauge can be attached to measure parallelism, flatness, and straightness.

## What is the flatness symbol?

GD&T Flatness is a common symbol that references how flat a surface is regardless of any other datum’s or features. It comes in useful if a feature is to be defined on a drawing that needs to be uniformly flat without tightening any other dimensions on the drawing.

## What are GD&T symbols?

Geometric Dimensioning and Tolerancing (GD&T) is a system for defining and communicating engineering tolerances. It uses a symbolic language on engineering drawings and computer-generated three-dimensional solid models that explicitly describe nominal geometry and its allowable variation.

## How does a CMM calculate flatness?

The flatness of the optically flat surfaces are measured by techniques using the CMM stylus. The stylus can be operated or programmed to take specific, accurate measurements along the surface of the object and compare the data automatically to produce a report on the flatness of the object.

## How is total runout calculated?

Another method for measuring total runout is to take one gauge held perpendicular to the surface of the part, and slowly move it across the surface of the part axially as the part is rotated. If the gauge varies at any point by more than the total runout tolerance, the part would be out of spec.

## How do you measure flatness with optical flats?

The bands should be viewed from a distance at least 10 times the diameter of the optical flat and with the line of vision as nearly perpendicular to the flat as possible. If the bands are straight, parallel and evenly spaced, the surface is flat. If the bands are curved or are unevenly spaced, the surface is not flat.

## 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.

## How is flatness defined?

In manufacturing and mechanical engineering, flatness is an important geometric condition for workpieces and tools. … Flatness may be defined in terms of least squares fit to a plane (“statistical flatness”), worst-case or overall flatness (the distance between the two closest parallel planes within).

## How do you calculate parallelism?

Using a Dial Gauge 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.

## What is straightness and flatness?

Surface: Straightness can be considered the 2-Dimensional version of Flatness as both are measured without a datum and controls and refine the size of the feature. While flatness measures the variance across a 2D plane, Straightness only measures the variance on a straight line.

## What are the 3 types of tolerances?

Three basic tolerances that occur most often on working drawings are: limit dimensions, unilateral, and bilateral tolerances. Three basic tolerances that occur most often on working drawings are: limit dimensions, unilateral, and bilateral tolerances.

## Does parallelism control flatness?

Remember: Parallelism does not directly control the angle of the referenced surface; it controls the envelope (like flatness) where the surface needs to be. The goal is to ensure all points are within a specified tolerance distance away from their corresponding datum points.

## How is perpendicularity calculated?

Surface: Perpendicularity is measured using a height gauge, similar to flatness, however, the gauge (or part) is locked to a 90° datum to measure how perpendicular the surface is. The entire surface has to be measured if it is a flat feature. See Example #2 below for a good example Axis Perpendicularity using MMC.