1、What Is Geometric Dimensioning 1. Provides a clear and concise technique for defining a reference coordinate system (datums) on a component or assembly to be used throughout the manufacturing and inspection processes. 2. Proper application of geometric dimensioning closely dovetails accepted and log
2、ical mechanical design process and design for manufacturing considerations. 3. Geometric dimensioning dramatically reduces the need for drawing notes to describe complex geometry requirements on a component or assembly by the use of standard symbology that accurately and quickly defines design, manu
3、facturing and inspection requirements. GD such as, the apex of a pyramid or cone, center point of a sphere or reference point on a surface for functional tooling or gauging purposes.19. Datum Reference - A datum reference is a datum feature.20. Datum Reference Plane - is a set of three mutually perp
4、endicular datum planes or axis established from the simulated datum in contact with datum surfaces or features and used as a basis for dimensions for designs, manufacture, and inspection measurement.21. Datum Simulator - A datum simulator a surface of adequate precision oriented to the high points o
5、f a designated datum from which the simulated datum is established. Examples: gage pin, block, surface of granite block.22. Diameter Symbol - the diameter symbol, indicates a circular feature when used on the field of a drawing or indicates that the tolerance is diametrical when used in a feature co
6、ntrol frame. 23. Datum Target - is a specified point, line, or area on a part that is used to establish the Datum Reference Plane for manufacturing and inspection operations. 24. Dimension - A dimension is a numerical value expressed in appropriate units of measure and indicated on a drawing.25. Fea
7、ture - Features are specific component portions of a part and may include one or more surfaces, such, as holes, screw threads, profiles, faces or slots. Features may be individual or interrelated.26. Feature Of Size - One cylindrical or spherical surface, or a set of two plane parallel surfaces, eac
8、h of which is associated with a size dimension.27. Feature Control frame (Symbol) - The feature control frame symbol is a rectangular box containing the geometric characteristics symbol, and the form, runout or location tolerance. If necessary, datum references and modifiers applicable to the featur
9、e or the datums are also contained in the box.28. Fit - Fit is a general term used to signify the range of tightness or looseness, which may result from the application of a specific combination of allowances and tolerance in the design of mating part features. Fits are four general types: interfere
10、nce, transition, line and clearance.29. Flatness - Flatness is the condition of a surface having all elements in one plane. Symbol: 30. Form Tolerance - A form tolerance states how far an actual surface of feature is permitted to vary from desired form the desired form implied by the drawing. Expres
11、sions of these tolerances refer to flatness, straightness, parallelism, perpendicularly, angularity, roundness, cylindricity, profile of a surface and profile of a line.31. Free State Variations - Free state variation is a term used to describe distortion of a part after removal of forces applied du
12、ring manufacture.32. Geometric Characteristics - Geometric characteristics refer to the basic elements or building blocks, which form the language of geometric dimensioning and tolerancing. Generally, the term refers to all the symbols used in form, runout, and locational tolerancing.33. Geometric T
13、olerance - The general term applied to the category of tolerances used to control form, profile, orientation, location, and runout.34. Implied Datum - An implied datum is an unspecified datum whose influence on the application is implied by the dimensional arrangement on the drawing; example, Coordi
14、nate dimensioning is applied to part, the zero dimension is attached to a feature this feature is implied as a datum element; axis, surface or plane.35. Interference Fit - An interference fit is one having limits of size so prescribed that an interference always results when mating parts are assembl
15、ed.36. Least Material Condition - (LMC) - This term implies that condition of a part feature of size wherein it contains the least (minimum) amount of material, examples, largest hole size and smallest shaft size. It is opposite to maximum material condition (MMC Symbol: 37. Limit Dimensions - In li
16、mit dimensioning only the maximum and minimum dimensions are specified. When used with dimension lines, the high limit is placed over the low limit. When used with a leader line or note, the low limit precedes the high limit.38. Limits Of Size - The specified maximum and minimum size of a given feat
17、ure.39. Limits of Size Concept - The limits of size concept calls for perfect form at maximum material condition. Also called the Taylor principle.40. Line to Line Fit - A line fit is one having limits of size so prescribed that surface contact or clearance may result when mating parts as assembled.
18、41. Location Tolerance - A tolerance states how far an actual feature may vary from the perfect location implied by the drawing as related to datums or other features. Expressions of these tolerances refer to the category of geometric characteristics containing position, concentricity, and symmetry.
19、42. Maximum Material Condition - (MMC) Maximum material condition is that condition of a part feature wherein it contains the maximum amount of material within the stated limits of size. That is: minimum hole size and maximum shaft size. Symbol: 43. Modifier - A modifier is the term used to describe
20、 the application of geometric principles. The principles include MMC, LMC, RFS, projected tolerance zone and diameter.44. Nominal Size - The nominal size is that stated designation which is used for the purpose of general identification, examples: 1.400, .050 .45. Parallelism - Parallelism is the co
21、ndition of a surface, line, or axis, which is equidistant at all, points from a datum plane or axis. Symbol: 46. Perpendicularity - Perpendicularity is the condition of a surface, axis, or line, which is 90 deg. From a datum plane or a datum axis. Symbol: 47. Position Tolerance - Position tolerance
22、(formerly called true position tolerance) defines a zone within which the axis or center plane of a feature is permitted to vary from true (theoretically exact) position. Symbol: 48. Principle Of Independency - This principle sets no limits to the number of errors of form possessed by individual fea
23、tures of a work piece. International designer, except the USA, use this principle.49. Profile Of A Line - Profile of a line is the condition permitting a uniform amount of profile variation, ether unilaterally or bilaterally, along a line element of a feature. Symbol: 50. Profile Of A Surface - Prof
24、ile of a surface is the condition permitting a uniform amount of profile variation, ether unilaterally or bilaterally, on a surface. Symbol: 51. Projected Tolerance Zone - A projected tolerance zone applies to a hole in which a pin, stud, screw, etc., is to be inserted. It controls the perpendicular
25、ity of the hole to the extent of the projection from the hole and as it relates to the mating part clearance. The projected tolerance zone extends above the surface of the part to the functional length of the pin, stud, and screw relative to its assembly with the mating part. Symbol: 52. Reference D
26、imension - A dimension, usually without tolerance, used for information purposes only. It does not govern production or inspection operations. A reference dimension is a repeat of a dimension or is derived from other values on the drawing or related drawings. Symbology: (.250)53. Regardless Of Featu
27、re Size - (RFS) - This is the condition where the tolerance of form, runout or location must be met irrespective of where the feature lies within its size tolerance. Optional for Position. Symbol: 54. Roundness - Roundness describes the condition on a surface of revolution (cylinder, cone, sphere) w
28、here all points of the surface intersected by any plane (1) perpendicular to a common axis (cylinder, cone), or (2) passing through a common center (sphere) are equidistant from the center. Symbol: 55. Runout - Runout is the composite deviation from the desired form of a part surface of revolution t
29、hrough on full rotation (360 deg) of the part on a datum axis. Symbol: 56. Runout Tolerance - Runout tolerance states how far an actual surface of feature is permitted to deviate from the desired form implied by the drawing during one full rotation of the part on a datum axis. There are two types of
30、 runout: circular runout and total runout.57. Size Tolerance - A size tolerance states how far individual features may vary from the desired size. Size tolerances are specified with ether unilateral, bilateral or limit tolerance methods.58. Specified Datum - A specified datum is a surface or feature
31、 identified with a datum identification symbol of note.59. Squareness - See Perpendicularity.60. Straightness - Straightness describes a condition where an element of a surface or an axis is a straight line. Symbol: 61. Symmetry - Symmetry is a condition in which a feature (or features) is symmetric
32、ally disposed about the center plane of a datum feature. 62. Tolerance - A tolerance is the total amount by which a specific dimension may vary; thus, the tolerance is the difference between the maximum and minimum limits.63. Transition Fit - A transition fit is one having limits of size so prescrib
33、ed that either a clearance or an interference mat result when mating parts as assembled.64. True Position - True position is the theoretically exact location of a feature established by basic dimensions, also referred to as “Position or positional tolerance“ Symbol: 65. Total Runout - Total runout i
34、s the simultaneous composite control of all elements of a surface at all circular and profile measuring positions as the part is rotated through 360. Symbol: 66. Unilateral Tolerance - A unilateral tolerance is a tolerance in which variation is permitted only in one direction from the specified dime
35、nsion, example, 1.400 +.000/ -.006.67. Virtual Condition (Size) - The boundary generated by the collective effects of MMC, size limit of a feature and any associated geometric tolerance, virtual condition must be considered in determining the fit between mating parts. The term “virtual condition“ is preferred over “virtual size.“
