![]() In the bottom half of the datum target frame, you write the letter/symbol indicating the same datum as that of the entire feature, along with the number of the datum target. Tolerance stack-up is limited to just two dimensions between any two positions within the pattern. The advantage of ordinate dimensioning is that it takes up far less space on a drawing, as shown in Figure 5. There are many datums and coordinate systems, each representing a different level of. This scheme also relies on a baseline, referred to as zero (0), from which all of the features are dimensioned. A system of coordinates is then used to describe those measurements relative to the datum, and a projection is the visual representation of those measurements on a different surface. Specifying a Datum TargetĪ datum target is described using a circular frame with a horizontal line drawn through the middle (datum target frame). A datum is simply a foundation and reference for spatial measurements. In such cases, you can indicate a datum target to define the minimum required part as a datum. Using a concaved bottom as a datum plane may also cause problems in placing it directly on the surface plate. Measuring under such conditions can result in deteriorated repeatability and reproducibility. If a plane defined as a datum is warped or otherwise shaped inappropriately, using that entire surface as a datum feature for indication can cause a significant error during processing or inspection. ![]()
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