Downloaded from https://www.everyspec.com EFFECT OF DIMENSIONING AND TOLERANCING ON INSPECTION 5-22. Introduction. When an Ordnance item symbols, and the implications of their use, leaves the design and engineering phases and should be thoroughly understood.
goes into production, dimensional control is exercised by inspectors who determine, by gag- The use of the datum surface symbol E in ing and, when necessary, measurement, thatthe conjunction with the tolerancing symbols, must items and components conform dimensionally to be carefully studied to assure that what is speci- te anducompents coform desion to fled on the drawing is in fact the requirement the requirements specified by the design en- which is needed. Examples of the requirements gineer. The dimensioning and tolerancing of an and use of the symbols follow. item impose difficulties on production and in- spection, unless presented in a proper manner.
The concentricity symbol i indicates that Ordnance Drawing 30-1-7, the surface to which it is applied, if made per- "Standard for Dimensioning and Tolerancing fectly, will have a common centerline with the "datum surface. Concentricity must not be con- has been established as a standard for dimen- fused with ovality (out-of-roundness), which is sioning and tolerancing of ammunition items, controlled by the diametral tolerance on each and the design engineer should understand thor- oughly the methods outlined therein and their surface.
Exampleo the drawing of the illus- pracica aplictio, i ordr tat iffculies trative piece shown on page 7 oi Drawing 30-1 -7 practical application, in order that difficulties in reproduced here in figure 5-11. Thetwocon- may be avoided In the production and inspection ditiona which may prevail (ovality and eccen- stages. The application of an incorrect symbol tricity) are shown in figure 5-12.
The ilhustrs- or requirement may result in the manufacture tfoe In figure 5-12a shows concentricity, but of a conwpoat that is not what the designer In- mimum permitted ovality; while figure 8-12b tended, but which the inspector must accept, shows maximum permitted eccentricity, but since it complies with the drawing. reo undnese. ,. # perfect roundness. The definition at dimensioning terms is clearly 17 stated on page 2 of Drawing 30-1-1. The en- gineer should bear In mind that a basic dimen- sion, although exercising control, is not checked .. .- . directly by the inspector. A reference dimen- sion, being informative only, is not a control dimension, and is not checked by the inspector.
P004 Generally speaking, only toleranced and datum dimensions are checked by the inspector. 5-23. Locational Tolerance Symbols. There are Fqrure 5-12. Concestrfcity requrement two classes of locational tolerance symbols U ovality is inherent in the part (thin-walled permitted, independent and dependent, and the sections of large diameters), the tolerance for difference between them is of great importance. concentricity should not be less than the sum of the diametral tolerances, unless a requirement 5-24.
An Indeendent Locational Tolerance is a for maximum ovality is included, because the fixed tolerance to whiP'h the manufacturer must inspection will not discriminate between ovality adhere, whether the part produced is of maxi- and eccentricity unless laboratory methods are mum permitted size or minimum permitted used. If the concentricity tolerance is leasthan size.
(See paragraph 5-25, on dependent leca- the sum of the diametral tolerances, the Inspec- tional tolerances, for comparison.) Independent tor will reject the parts for failing to conform locational tolerance requirements are specifi- to the concentricity requirement (the diametral caily checked by the inspector independently of gages having accepted the parts), in spite of the other requirements, normally by the use of dial fact that the parts might be perfectly concentric indicating gages. The application of the various but out-of-round. 5-13 ____• ___ I