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Thread: features on a common centerline with no positional tolerance

  1. #1
    Associate Engineer
    Join Date
    Feb 2014

    Question features on a common centerline with no positional tolerance

    I have a drawing for a custom shoulder bolt. The od requirement is .0925+/-.0005. The thread is .086-56 unc-3a. There are no concentricity or runout tolerances specified. the drawing does reference y 14.5. What would be the allowable runout or concentricity requirement? Does the envelope principle apply?

  2. #2
    Project Engineer
    Join Date
    May 2011
    Nope -- the envelope principle says that size controls form, but there is no control over location. So you've come up against a quite-common oversight: while it's true that features drawn as coaxial are implied as coaxial, there is no automatic tolerance for how coaxial they must be.
    Perhaps the thinking was that with threads it's not a huge issue since the threads are cut from the major diameter. "C'mon, how far off will the threads be?" But of course that's when Murphy's Law kicks in...

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