#Primary datum software
#Primary datum iso
#Primary datum simulator

This collection of datums suppresses all six degrees of freedom of a component when it is assembled into the product. form) specification should be attached to it on the drawing.Ī datum system is a collection of two or three datum elements that are based on several separate surfaces chosen with a functional hierarchy giving rise to primary, secondary, and tertiary datums. In addition, for the datum feature to be a “good” functional reference, a flatness (i.e. The default association rule to apply here is to place the perfect datum A plane as externally tangent to the highest points of the real datum feature. You can see in blue that datum A is a theoretical plane associated with the shaded surface, the datum feature, which is real surface of the part shown with exaggerated unevenness. To further visualize the relationship between a datum feature and a theoretical datum reference, below is a view of the above illustration in 3D.

#Primary datum simulator

In the case of a cylindrical shaft specified with a line datum, that datum feature simulator might be a lathe chuck in which the shaft is mounted. For instance, datum feature A could be placed on a flat table, acting as the datum simulator, from which the distance to the toleranced feature surface can be measured with a micrometer, or other metrology device like a 3d scanner, to ensure it is between 24.95 mm and 25.05 mm. To measure an actual part like this one to ensure it is within tolerance, the datum feature surface would be placed on what is called a datum feature simulator, which is a physical surface or device that simulates the conceptual datum. Also note that the size (width, diameter) of a tolerance zone is ALWAYS specified in linear dimension units, here mm, even when the specification is for orientation ( i.e. Specifying a positional tolerance for a plane in ASME makes use of the surface profile symbol.

#Primary datum iso

Note that the symbol of a cross combined with a circle used in the above example of FCF for specifying a positional tolerance is used in ISO for both planar and cylindrical surfaces, whereas it is used in ASME only for cylindrical surfaces. On the right is an illustration of the part with magnified real, uneven surfaces showing what the markups communicate. On the left is an illustration of ISO GPS markup for a datum and specified dimension within a drawing of a simple part. Choosing datums wisely for tolerance analysis.This article covers the following datum topics:

#Primary datum software

The representation of datums to support GD&T design decisions are core to tolerance analysis software products, such as Enventive Concept. The goal is to efficiently define a set of datums that theoretically remove the six modes in which a part can independently move (three linear and three rotational) - in other words to suppress its degrees of freedom. The best choice of datums for efficient tolerance stackup calculations is to use those surfaces that are positioning the parts within the assembly. For instance an automotive hinge or latch that is built with excessive variations might not correctly close what it is attached to or it could open unexpectedly.

Tolerance analysis must ensure that these accumulated variations do not adversely impact the functionality of the product. Once all those components are assembled, each of their variances accumulate across the combinations of those components, or what are referred to as stackups.

The goal with datums is to conceptually remove a part’s degrees of freedom so it can be correctly fabricated and then measured to ensure it meets design specifications - in this example three datum planes immobilize a part’s linear X, Y, Z and rotational u, v, w movements.ĭatums are especially important in tolerance analysis, which is the process of determining how much variation in size and shape is allowed for each of a product’s individual parts (also often referred to as components).