![]() Datum points do not play any rule in part form, fit, and function directly. You may like to read: What is Datum in GD & T Why datum targets use basic dimension?įirst of all, we need to understand that data points are virtual or imaginary points to establish the datum to sit on the fixture. When there are three touch points then it is a primary datum, for two points it is a secondary datum and for one touchpoint it is the tertiary datum. When we connect those datum points, we get the virtual datum. Those datum points should not be in a line. To create datums from datum targets, there should be a minimum of three datum points on a surface. So instead of declaring a whole surface as a datum, which is not possible for irregular surfaces, the engineer shows data points that should contact the data feature simulator-a fixture or measuring equipment to establish simulated datums. Due to this, there is a high chance of measurement error. If you place those parts on the fixture, the part will never sit on the surface, and it may wobble. Manufacturing operations like molding, casting, forging has irregular surfaces. You may like to read: What is MMC and LMC in GD & T Why datum targets are required? ![]() Datum targets create those virtual datums. So it is essential to establish a virtual datum that can come in contact with the surface of the fixture for measurement. ![]() ![]() We all know that irregular surfaces are difficult to measure as they can not be placed properly on any fixtures. Can the diameter symbol be used when the datum target area is round? What is a datum target? Datum target definitionĭatum targets are set of points, line or area required to establish datum on irregular surfaces.What dimension is placed in the lower and upper half of the datum target symbol?.What is a datum target? Datum target definition. ![]()
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