# Relationship between flatness and parallelism definition

### GD&T Parallelism Definition | eMachineShop

With, parallelism, a reference is made to a datum plane, while flatness is a block on a surface plate whose three points of contact define the -A- datum plane. What's the difference between the camber, flatness, and parallelism of a T = Substrate mode of thickness, where the mode is defined as the. Parallelism is not often used in a tolerance stack except when it is applied to a surface, in which case it is treated like a flatness control since it refines the.

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.

### GDT: Parallelism vs. Flatness

Parallelism is quite simple to measure. Like flatnessa gauge is run across the reference surface or feature. However unlike flatness, the part is constrained against a granite block or flat plane that acts as the datum surface where it is measured.

All the profiles of orientation and are used in the exact same way.

## GD&T Parallelism Definition

All of the orientation symbols angularity, perpendicularityand parallelism all call out the particular feature envelope referenced to a datum.

Whenever two surfaces or features need to work in sync with each other and constant distance must be maintained, parallelism is effective. Even though surface parallelism seems to ensure that a flat surface is mating with another flat surface, it can also be applied to two sides of a hole or cylinder to avoid a taper. Any part with two critical flat surfaces such as gears, would call out parallelism. A gear has to maintain constant axial load on both faces.

## GD&T Symbols

To ensure even contact one side of the gear is held parallel to the other side. To do this without parallelism, the gear width would have to be tightly controlled, which could be very difficult to do. Combination of Orientation and Form: Parallelism is very common in its surface form.

It's some of the most basic geometry you'll need to understand. Just do everyone a favor and don't make it any more difficult than you need to.

Flatness is a feature compared to itself, while parallelism requires that a feature be compared to a datum. To clear up the concept, consider the example of a kitchen table. We purchase a new table from a furniture store and are fairly certain that the flatness of the tabletop to be less than a fraction of an inch.

If the table legs are the same lengths within a few fractions of an inch, we can be confident the tabletop is parallel to the kitchen floor. The table top is flat and because the length of the legs is equal the top is ALSO parallel to the kitchen floor.

After this is accomplished, we use an indicator to measure the out-of-flatness of the "top"surface and, in effect, measure the surface against itself.

The table top is still just as flat but it's no longer parallel to the floor. If we want to measure the parallelism of one side we'll say the bottom to the other side the topwe 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.

Even though the top and bottom faces of the part are flat, they are not parallel to the Datum.