Downloaded from https://www.everyspec.com the design of ammunition items when the inde- pendent symbol I is applicable. However, in many instances where assembly is the prime requisite, a dependent locational symbol Indi- cating a requirement for centrality may be used to advantage, and a discussion of this point is to be found in paragraph 5-25. It should be emphasized that the independent symbol refers to total variation and LA-004 not to displacement of centerlines. This is easily understood if it is remembered that the centerline of the designated form may vary 0.002 on either side of the centerline of the da- tum form, thus allowing a total variation of A 0.004.
Figure 16 of Drawing 30-1-7 illustrates a Joint READING NOT TO EXCEED .004 requirement for concentricity and perpendicu- WHEN ROTATED 300 larity. The prime requirement is for concen- tricity of the 0.874 diameter with the pitch di- ameter specified as the datum ='3J. The secondary requirement is that the effect of lack of perpendicularity between the 0.874 diameter and the end surface [ shall be included with the eccentricity in the total variation of 0.004 which may be indicated on the dial.
-- Since there is no specific rqurement for per- - pendicularity of surface E with the pitch I diameter E , the combined requirement in- dicates that if the surfaces are concentric, then the play of the mating threads may allow sur- face M-] to be out of perpendicular with the L pitch diameter within 0.004 on the dial reading taken at the opposite end of the piece. Figure SURFACE PLATE 5-16 shows schematically the effect of each re- quirement, and of the combined requirement. Figure 17 of Drawing 30-1-7 shows the prime requirement of concentricity of the threaded counterbore with the datum counterbore, and Figure 5-13.
Requirementfor perpendicularity the secondary requirement of perpendiculari of the counterbores with the end surfaces-Ji_) the part is acceptable. Figure 5-17 shows the and [ . In addition, there is an implied effect of cocked centerlines on dial readings. requirement that the effect of lack of parallelism 5-25. A Dependent Locational Tolerance is a of the axis of the screw thread with the center- v ariable, since the effect of assclated damen- line of the base counterbore shall be includedin atonal tolerances alfects the magnitude of the the total variation. This is implied by the sym- locationsl tolerance.
Dependent loeational to!- bol [F-- , which indicates that the total vani- erances are inspected by functional gages, which ation must not exceed 0.004 when readings are simulate the mating parts. This type of tol- taken at gaging positions located 0.25 and 2.50 erance should be used when facility of assem- inches beyond end surface E-•---. The greater bly is the prime factor. Examples of dependent length usually compares with the length of the tolerance symbols are shownin Drawing 30-1-7, mating part. If neither dial exceeds 0.004, then pages 12 through 16. 5-15