Why gdt important

In Figure 5 the part is aligned to best fit. Shape and position deviation are evaluated independently from each other. This example might be a bit exaggerated, but it shows very clearly the challenge when exclusively using the traditional way of dimensioning and tolerancing.

And remember, you still do not have any idea what the function of this part could be. It seems to be important that the two sides are nearly parallel, and it is probably fixed at the short side. Figure 6. Figure 7. This way of communication promotes a uniform understanding and interpretation among all involved persons, including a description how to measure the deviation. To identify the deviation correctly it is important to describe how to position the part for measurement.

This happens via datums. For making sure the positioning is repeatable the datums should fulfil a predefined quality. Let us assume you want to make sure that the long side is parallel to the short side within a defined tolerance. As first you define the short side as datum A. It is important to give every datum a profile tolerance, in our case a flatness of 0. In the next step you give a positioning tolerance 0.

We are an employee-owned custom injection molder with experience, capabilities, and state-of-the-art facilities that allow us to handle simple to complex operations throughout all stages of your project. Search for:. What is Geometric Dimensioning and Tolerancing? DRF is the frame of reference and origin of all dimensions and geometric specifications on a given drawing. Datums : these are the points, lines, and planes that make up the DRF in drawings and are the exact anchors to which the part dimensions and tolerances are referenced.

It is important to keep in mind that datums are theoretical, and therefore, perfect. Datum Features: these are the features of the part such as holes. Datum features are real and tangible, and therefore, have variation. In addition, all necessary dimensions of the end product must be defined and the use of reference dimensions kept to a minimum. The dimensions must also be selected and arranged according to the function of the part and its relationship with mating parts.

A datum can be described as a theoretical exact plane, point or axis location from where the remaining features of a part are referenced from. Dimensional tolerances are referenced to the datums. The DRF concept describes the creation of three mutually perpendicular and theoretically perfect planes.

The three planes are required for manufacturing and inspecting a part to the drawing, and detailed below:. Through the process of designating three mutually perpendicular datum planes you have established the Datum Reference Frame DRF.

The geometric tolerance for an individual part feature is indicated within the Feature Control Frame, which is divided into separate compartments. In the first compartment you place the symbol for the geometric characteristic you are defining, such as true position, profile or runout. The second compartment contains the tolerance call-out. In some cases the tolerance may be preceded by a diameter symbol.

The datum planes should be placed in the remaining compartments.