Indirect Flatness Controls There are several geometric controls that can indirectly affect the flatness of a surface they are Rule #1, perpendicularity, parallelism, angularity, total runout and profile of a surface. This is when a flatness control is specified on a drawing: When these types of applications are involved, the indirect flatness control that results from Rule #1 is often not sufficient to satisfy the functional requirements of the part surface. Ġ.4 FLATNESS ERROR 0.4 FLATNESS ERROR MMC Part would have to be perfectly flat on both sides LMC Part could have 0.4 flatness error on both sidesįlatness Control Application Some examples of when a designer uses flatness control on a drawing are to provide a flat surface: For a gasket or seal. Rule #1 Effect on Flatness Since Rule #1 provides an automatic indirect flatness control, a flatness control should not be used unless it is a refinement of the dimensional limits of the surface. As the feature departs from MMC, a flatness error equal to the amount of the departure is allowed. Rule #1 Effect on Flatness When the feature of size is at MMC, both surfaces must be perfectly flat. Rule #1 Effect on Flatness Whenever Rule #1 applies to a feature of size that consists of two parallel planes, an automatic indirect flatness control exists for both surfaces. The distance between the parallel planes is equal to the flatness control tolerance value. Interpretation of Flatness tolerance : It consists of two parallel planes within which all the surface elements must lie. The tolerance zone for a flatness control is three-dimensional. įLATNESS Definition : Flatness is the condition of a surface having all of its elements in one plane. Goals and Objectives Interpret the flatness control. Ĭreating a partial reference frame from offset surfaces(contd…)Ĭreating a partial datum reference frame from irregular surfacesįor the figure, sketch the simulated datums for the datum target įORM CONTROLS FLATNESS STRAIGHTNESS CIRCULARITY CYLINDRICITY 3.The part dimensioning must ensure that the part will rest in the gauge in only one orientation and location. 2.The datum reference frame must restrain the part in all six degree of freedom. Basic dimensions should be used to define and locate the datum targets. When using datum targets to establish a complete datum reference frame, three requirements should be met: 1. ĭATUM TARGETS SYMBOLS(contd….) Datum target point ĭATUM TARGETS SYMBOLS(contd….) Datum target line ĭATUM TARGETS SYMBOLS(contd….) Datum target areas ĭATUM TARGETS APPLICATIONS Although there are only three datum target symbols, they can be used in a variety of ways and on a number of different types of parts. Basic dimensions should used be used to locate datum target points relative each other and the other datums on the part. ĭATUM TARGETS SYMBOLS(contd….) A datum target point is specified by an X shaped symbol, consisting of a pair of lines intersecting at 90 °. Three symbols used to denote the type of gauge element in a datum target application are the symbols for a target point, a target line, and a target area. The leader line from the symbol specifies whether the datum target exists on the surface shown or on the hidden surface side of the part. ĭATUM TARGETS SYMBOLS A datum target application uses two of symbols: 1.A datum target identification symbol 2.Symbols that denote which type of gauge elements are to be used. Datum targets should be specified on parts where it is not practical (or possible) to use an entire surface as a datum feature. The use of datum targets allows a stable and repeatable relationship for a part with its gauge. Datum targets can be specified to simulate a point, line or area contact on a part. Datum targets are shown on the part surfaces on a drawing, but they actually do not exist on a part. DATUM TARGETS Datum targets are symbols that describe the shape, size and location of gauge elements that used to establish datum planes or axes.
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