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If You Want Location - Use Locating Controls
(In accordance with Y14.5M-1994 standard)

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As pointed out in last month’s Tip, size and form tolerances do not control location.  On the Spool drawing, it is intended that the individual lands align with one another.  The upper drawing could result in the part shown to its right.  Locating tolerances include profile of a surface and position.  To align the lands, one of these controls should be used.  The profile of a surface approach might be used if the assembly area is making matched pairs and cannot have interchangeability where the size tolerance is beyond the process capability.  Where the processes are capable of holding the size and alignment (position) of the lands, the position control would assure interchangeability.

Note:  Although no datum reference has been used on the position callout, position when applied to a pattern controls the features within the pattern.

Back to Tips Tip added Nov 2002