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Geometric orientation of holes on round part?

Geometric orientation of holes on round part?

Geometric orientation of holes on round part?

(OP)
Is this the correct way to position a four-hole pattern to a single hole and tie them together radially on the face of a round part were a center hole (B) and the face (a) are the only datums. Our discussion is over the clarity as drawn.

Center lines are shown perpendicular with the single hole at the 270 degree position, one of the holes from the four hole pattern is shown being 45 degrees off the 0 degree line with the 4 x 90 degrees shown to the next hole at the 135 degree position.  Both the four-hole pattern and the single hole have separate positional call outs to the face datum A and the hole datum B.

Does this automatically tie the holes to each other?
Would it be better to make either the four-hole pattern or the single hole a datum and position the other to it?

Thanks for your help.

RE: Geometric orientation of holes on round part?

According to ASME Y14.5M-1994, the single hole and the four-hole pattern you described (5 holes total) are considered to be a simultaneous requirement if the feature control frames for each callout references the same datums, in the same order of precedence, and uses the same material condition modifier for the datum feature of size (datum B in your example).  This is stated in the standard at two locations as follows:

"4.5.12 Simultaneous Requirements. Where two or more features or patterns of features are located by basic dimensions related to common datum features referenced in the same order of precedence and at the same material condition, as applicable, they are considered a composite pattern with the geometric tolerances applied simultaneously as illustrated by Fig. 4-26. If such interrelationship is not required, a notation such as SEP REQT is placed adjacent to each applicable feature control frame. See para. 5.3.6.2, and Fig. 5-18."

This concept is also described in the positional tolerance section(Section 5)as follows:

"5.3.6.2 Simultaneous Requirement - MMC.  Where any of the common datums in multiple patterns of features is specified on an MMC basis, there is an option whether the patterns are to be considered as a single pattern or as having separate requirements. If no note is added under the feature control frames, the patterns are to be treated as a single pattern. Where it is desired to permit the patterns to be treated as separate patterns, a notation such as SEP REQT is placed beneath each feature control frame. See Fig. 5-18. This allows the datum features of size to establish a separate datum reference frame for each pattern of features, as a group. These datum reference frames may shift independently of each other, resulting in an independent relationship between the patterns. This principle does not apply to the lower segments of composite feature control frames except as noted in para. 4.5.12.1."

Based on the above conventions, the 5 holes you described are verified as a single pattern.

Hope this helps

GDTGUY

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