#Catia hole callout series#

Commonly in manufacturing and design you would say вЂњdatumвЂќ to cover everything just for simplicity. *Note: It is common to simply use the term вЂњdatumвЂќ when referring to a datum feature or a datum since, in a perfect world, they would be the same. They are usually important functional surface. In the above drawing, this surface may be simulated by a near perfect granite slab.Дatums are theoretical and only simulated by Measurement Equipment (Gauge pins, Granite slabs, angle plates, computer-generated planes, etc)Дatum FeaturesВ are real, tangible features on a part where the measurement equipment would physically touch or measure. For example,the face of a flat part may be referenced by a datum on a drawing. To form this theoretical plane in the real world, measurement surfaces or points are used. In the example above, the Datum is the greenВ line and the Datum Feature is the imperfect black line that forms it. It will always have some kind of waviness, bumps and valleys. The reason they are not equal to each otherВ is because theВ part surface is never 100% perfect. However a Datum Feature is a tangible surface, point or axis on a part where that theoretical datum is located. A Datum is a perfect point, line, plane or surface but only exists theoretically. However, things get a little tricky when clarifying what the datum actually is. Shown on the side view by denoting the axisДЄ datum feature is usually an important functional surface where all other dimensions need to be in spec with reference to it.Placed on the feature control frame itself вЂ“ Example C.Placed on the leader pointing to the hole вЂ“ Example B.Placed directly on the hole вЂ“ Example A in the above drawing.To establish a datum axis of a feature such as a hole, the symbol can be placed in a few ways. This type is common with any GD&T symbol that can have axis control like runout, perpendicularity or concentricity. This means that the datum is actually the central axis through the feature, and not the feature surface itself. On an AxisДЇor Axis control, the symbol must be placed on the dimension of a diametric tolerance as shown above. However if the part is round like a cylinder, the datum would be the entire surface of the cylinder. If itВ is on one side of a rectangular object like a box, the datum surface is only the side where the symbol is shown. This means that the datum is only on the surface of the part where it is shown. The symbol must be placed on or with one single extension line out of the datum surface. Here is how different types of features are called out on engineering drawings. It is important though that theyВ is called out correctly on the drawing to control the right type of feature. A feature control frame can reference multiple datums at once and eachВ oneВ can be referenced as many times as needed.ДЄs stated before, datums can be located on points, axes,edges, and surfaces. This letter will also show up in any feature control frame that uses this datum feature as a reference. These letters are in boxes and tied to the datum feature with a black triangle.

#Catia hole callout series#

The datum features on a drawing are denoted with a series of capital letters. How Datum Features are Shown on a Drawing When it comes to GD&T, datum symbolsВ are your starting points where all other featuresВ are referenced from. A datum feature is usually an important functional feature that needs to be controlled during measurement as well.ДЄll GD&T symbols except for the form tolerances ( straightness, flatness, circularity and cylindricity) can use datums to help specify what geometrical control is needed on the part. You can think of themВ as an anchor for the entire part where the other features are referenced from. A datum is theoretical exact plane, axis or point location that GD&T or dimensional tolerances are referenced to.