Dimensioning and Tolerancing, Section 6, Drafting Manual

1 GENIUM PUBLISHINGS ection 1 February 1997* Drafting MANUALD imensioning and TolerancingSymbolsUpdate 56* Supersedes issue of September Diameter - A diameter symbol is placed in front of anydimension value that is a diameter. See Figure 2. Diameter Counterbore Symbol - A counterbore symbol combinedwith a diameter symbol is placed in front of a specifiedcounterbore or spotface diameter. See Figure 3. Counterbore Countersink - The countersink symbol combined with adiameter symbol is placed in front of a specified countersinkdiameter. See Figure 4. Countersink GENERAL1 This Section is based on ASME Symbols uniqueto ANSI are also described for those who arecontractually obligated to comply with the older Symbols permit consistency in the way dimensions andtolerances are specified, and each symbol has a clearly definedmeaning.

2 Symbols take less time to apply on a drawing thanwould be required to state the same requirements with symbols also require considerably less space. See Figure 1. Equivalent Symbol and The symbols are presented in two groups for easier use ofthis Section as a reference. General Dimensioning symbols areshown first. Some of these symbols are also used in tolerancespecifications. The second set of symbols are used for Symbol sizes are shown in the figures as values propor-tional to the letter h . The letter h represents the predominantcharacter height on a drawing. If a symbol dimension is shownas , and the predominant character height on the drawing isto be 3mm, then the symbol dimension is ( x 3mm).

3 Symbol proportions defined in the standard are recommen-dations. Some companies find it desirable to vary from therecommended proportions for improved microfilm reproduc-tion capability. Symbol proportions within a company, andcertainly within a single drawing, should be Symbols are not generally used in text or notes and symbol names are used in text or notes GENERAL SYMBOLSG eneral symbols are used with dimensions to clarify therequirement defined by a dimension value and to minimize thenumber of words or abbreviations placed on a 56by: Bruce A. Wilson1 Figures in this Section were created using Auto CAD software, a product ofAutodesk, Inc. and plotted on a Summagraphics (Houston InstrumentEngineered) DMP 160 series Drafting MANUALPage 2 Dimensioning and TolerancingAugust 1993*SymbolsUpdate Depth - A downward-pointing arrow is used for the depthsymbol, and it is placed in front of the depth value in suchapplications as for counterbore and hole depths.

4 See Figure 5. Depth Dimension Origin - A circle used in place of one of thearrowheads on a dimension line indicates the origin formeasurement. See Figure 6. This symbol is not used as areplacement for datums and datum Reference -Parentheses enclosing adimension valueindicates the dimensionis a reference Figure Square - A square is placed in front of dimensions forsquare features. See Figure 7. The square symbol is used in amanner similar to the diameter symbol. One dimension isadequate for a square shape when this symbol is used -eliminating the need for a second 9. Arc Arc Length - An arcdrawn above a dimensionvalue indicates the shownvalue is the distancemeasure along the definedarc.

5 See Figure 9. It maybe a distance measuredalong a curved surface orit may be a distancebetween two features suchas holes in a curved part.* Supersedes issue of September 1984 GENIUM PUBLISHINGGENIUM PUBLISHINGS ection 3 February 1997* Drafting MANUALD imensioning and TolerancingSymbolsUpdate 56* Supersedes issue of September 1995example:3X .250-20 UNC-3 AThe letter X can also be used in place of the word BY. A spaceis placed on each side of the letter X for this :.125 X . Radius - The letter R isplaced in front of any value thatindicates a radius dimension. SeeFigure 12. Prior to the 1982standard, the letter R was shownfollowing the dimension 12. Radius Controlled Radius - The abbreviation CR is defined bythe 1994 standard to indicate a controlled radius - This abbreviation is not defined in the Spherical Radius -The letters SR are placed infront of a dimension for aspherical radius.

6 See Fig-ure 13. Spherical SphericalDiameter - A letter Sprecedes the diametersymbol, and both areplaced in front of aspherical diameterdimension. SeeFigure 14. Spherical tolerancing SYMBOLST olerancing symbols can be categorized as being applicable todatum identification, form, orientation, location, profile, runout,and Slope - The slope symbol is placed at the left end of theslope specification. See Figure 10. The slope value is specifiedas the amount of change per unit of 10. Slope Conical Taper - A conical taper symbol is placed in frontof a taper specification. See Figure 11. The specificationindicates the amount of change in diameter over a unit lengthof the 11. Conical Taper LETTERS - All letters used for symbols have a heightequal to h.

7 Letter X - The letter X may be used to indicate anumber of times or places a feature or item is repeated. If the Xis to indicate the number of times or places, no space is shownbetween the number of occurrences and the letter X.*Supersedes issue of August 1993 Section 4 June 1996*GENIUM PUBLISHINGDRAFTING MANUALD imensioning and TolerancingSymbolsUpdate 55* Supersedes issue of September DATUM IDENTIFICATION SYMBOLS - Thesesymbols provide a means to identify datum 1994 Datum Feature Symbol - This symbol became standard in 1994 and is used widely in foreign countriessince it is defined by the International Standards Figure 15. 1994 Datum Feature The 1994 symbol always has a leader extending from itto the point of application.

8 The leader includes a triangle at theend. It may be filled or left open. The triangle is sometimesreferred to as a suction cup, but it is correctly identified as adatum feature 16. 1982 Datum Feature 1982 Datum Feature Symbol - The symbol shown inANSI and earlier standards is a rectangle withtwo short dashes. See Figure 16. One dash is placed on eachside of the letter used to identify the datum feature. Dependingon the requirement, this symbol may be attached to an exten-sion line, a dimension line, a leader, a feature control frame, orplaced adjacent to a dimension Datum Target Symbol -The datum target is a circlewith a horizontal line acrossthe middle. See Figure datum identification goesin the bottom half of thesymbol, and, in the case of adatum area, the size can beshown in the top 17.

9 Datum Target Target Point Symbol - Adatum target point is shown bydrawing an X at the locationof the point. See Figure same symbol is also usedto indicate the end view of adatum target 18. Datum Target Point FORM - Form tolerance symbols include straightness,flatness, circularity, and cylindricity. Although profile can beused to control form, profile tolerance symbols are contained ina separate category of 1995 Drafting Manual Section and tolerancing Page 5 Update 47 Symbols August 1993* Straightness - A straightline is used to indicate astraightness requirement.

10 SeeFigure 19. It is only applied in afeature control frame, and maybe used to control straightness ofsurface elements. It may also beused to control the straightness ofan axis or center Flatness - Theflatness symbol appearsas an oblique view of asquare surface. SeeFigure 20. This symbol isused in feature controlframes and is only usedto control the formvariations on Circularity - Circularity isindicated by a circle. See Fig-ure 21. It controls the amount ofform error permitted on thesurface of a circular feature atindividual cross Cylindricity - Thissymbol is a circle withtwo parallel lines drawntangent to the circle. SeeFigure 22. It is used tocontrol the surface errorson a cylindrical simultaneouslycontrols circularity andparallelism of theelements on the ORIENTATION - Orientation tolerance symbols includeparallelism, perpendicularity, and Perpendicularity -Perpendicularity is indicatedby two perpendicular Figure Parallelism - Parallel-ism is indicated by twoparallel straight lines.