Obviously, the hole's basic orientation is 0° and its basic offset from center is 0. › Implied zero-basic dimensions: The view implies the relationship of the Ø.750 hole to the planes of the DRF as represented by the view's center lines.Since the holes appear symmetrical about the center plane of the DRF, that symmetrical basic relationship is implied (ngụ ý, bao hàm, ám chỉ). The true positions of the two Ø.750 holes have a single 3.000 basic dimension between them, but no dimension that relates either hole to the planes of the DRF. › Implied symmetry dimensioning: In many cases, the applicable basic dimensions are iplied by drawing views.A manufacturer needing the coordinate of the lower hole will have to calculate it 1.500 – 2.500 = – 1.000. We often confuse the 2.500 basic as originating from the actual axis of the upper hole, rather than from its true position. However, the lower Ø.500 hole is located with a 2.500 basic dimension from the true position of the upper hole. › Chain dimensioning: A basic dimension of 1.500 locates the upper Ø.500 hole directly from the center plane.CMM inspection is simplified, using a single 0,0 origin for both holes. Manufacturers prefer this method because it directly provides them the coordinates for each true position relative to the datum origin. › Base line dimensioning: For each of the two Ø.376 holes, a basic dimension originates from each plane of the DRF. ![]() The basic dimensions may be shown graphically on the drawing, or expressed in table form either on the drawing or in a document referenced by the drawing. True position is the nominal or idal orientation and location of the feature and thus, the center of the virtual condition boundary or positional tolerance zone. ![]() It can be used with MMC (Max Material Condition), LMC (Least Material Condition), projected tolerances (P), and tangent planes (T).ĭimensions for True Position: For each individual controlled feature, a unique true position shall be established with basic dimensions relative to a specified DRF (Datum Reference Frame). Depending on how it is called out, true position can mean several different things. Expressed as the total permissible variation that a feature can have from its “true” position. True Position is the theoretically exact location of a Feature of Size (FOS) defined by basic dimensions. Each datum reference may be followed by an MMC or LMC modifying symbol, as appropriate to the type of datum feature and the design. Any additional modifiers, such as "statistical tolerance," and/or "projected tolerance zone" followed by one, two or three separate compartments, each contaning a datum reference letter. Within the compartment, the positional tolerance value may be followed by an MMC or LMC modifying symbol. How to Apply It? A positional tolerance (kích cỡ, khối lượng, của một bộ phận có thể dao động mà không gây tác hại) is specified using a feature control frame displaying the "position" characteristic symbol followed by a compartment containing the positional tolerance value. A boundary, defined as the virtual condition, located at the true theoretically exact position, that may not be violated by the surface or surfaces of the considered feature of size. › When specified on an MMC or LMC basis, a TOP control defines a boundary – often referred to as the virtual condition – that may not be violated by the surface or surfaces of the considered feature.ģ.› When specified on an Regardless Feature of Size (RFS) basis, a TOP (tolerance of position) control defines a tolerance zone that the center, axis, or center-plane of the " Actual Mating Envelope (AME)" of a POS must be within.A position tolerance may be specified in an RFS, MMC, or LMC context. A zone within which the center, axis, or center plane of a feature of size is permitted to vary from a true (theoretically exact) position.Ģ. How Does It Work? A positional tolerance defines either of the following:ġ. Only feature of size can have a position tolerance applied to them. Surfaces cannot be controlled with a position tolerance (surface can be controlled with a profile of a surface tolerance). Position (xác định vị trí) is the perfect location of a feature of size in relation to a datum or datums. ![]() This control provides an opportunity to utilize (dùng, sử dụng tận dụng) many of the advantages of GD&T. ![]() Position should be specified whenever the design requirements permit. Position is a versatile (nhiều tác dụng đa năng) tolerance that can be used to control location, coaxiality, orientation or axis offset of a part feature or axis. TOLERANCES OF LOCATION - TOLERANCE OF POSITION
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