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Datum Features • Datum features do not actually exist on a real part • Datum features cannot be seen or felt • Datum Features help locate and define part features • There are three principle types of datum features • Datum Points • Datum Axes • Datum Planes
Datum Points Datum points may be used to place holes and other features FIGURE 6.46. Various ways to define a datum point.
Datum Axes Datum axes are often used when creating revolved solids and circular arrays. Datum Axes are also used to indicate directions during a variety of modeling tasks. FIGURE 6.47. Various ways to define a datum axis.
Datum Planes Datum planes are often used to create sketches & holes, and also perform mirror operations. Datum Planes are very helpful and are commonly used. FIGURE 6.48. Various ways to define a datum plane. More ways to define a datum plane.
Chaining Datums Using simply-defined datums to create more complex datums FIGURE 6.49. To create a datum plane that is tangent to a cylindrical surface at a specific location, an intermediate datum plane, shown in (a), can be created through the centerline of the cylinder. The intersection of the intermediate datum with the cylinder creates a datums axis that is used to locate the final datum plane.
Feature Arrays • A Feature Array takes one feature and places copies of it on the model at specific spacing. • If the “master” feature is modified, the changes appear on the arrayed copies FIGURE 6.50. A rectangular array of protrusions created from a master feature.
Rectangular and Circular Arrays Circular Array Rectangular Array
Mirrored Features FIGURE 6.53. Creation of a mirrored feature. The master feature in (a) is mirrored by creating a datum plane as a mirror plane (b). A mirror image of the feature is produced on the opposite side of the datum plane in (c), and the final result is shown in (d).
Mirror Solid Half of a solid body is mirrored by creating a datum plane as a mirror plane. A mirror image of the solid body is produced on the opposite side of the datum plane.
Associativity in Arrays and Mirror Operations • Creating “Instances” of the master feature or solid body • An associative link is maintained between the master and the newly created features or solid (children). • Changes made to the master are reflected on the children • Associative link may be broken if desired (in some, but not all, modelers)