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Thread: Tolerance of holes shown on centerlines

  1. #1

    Tolerance of holes shown on centerlines

    Does anyone know what the tolerance would be when two holes are placed on a centerline? The attached image has two holes highlighted. Vertically they have a tolerance of ±.002. Horizontally they fall on the centerline. Since horizontally ±.000 is not possible and there is no dimension from the centerline that would make title block dimensions applicable, what would the tolerance be when GD&T is not applied. Per the title block, the standard is ASME Y-14.5 1994.
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  2. #2
    Administrator Kelly Bramble's Avatar
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    Welcome to EE!

    The engineering drawing should have a default tolerance block on it somewhere. Many organizations use the decimal place method.

    For example:
    .xx = +/- .03
    .xxx = +/- .010
    .xxxx = +/- .0010

    The diameters have distance dimensions associated with them that are .xxx. So, the cylinder to cylinder location tolerance should be +/- 0.10 should this be the default tolerance case.
    If there is not a default tolerance specified you need clarification.

  3. #3
    Thanks for the response Kelly.

    There is a default tolerance block on the drawing using the method you stated.

    Is this correctly stated (using the default tolerances from your example): The cylinders are allowed to move ±.002 vertically (according to the stated tolerance) and ±.010 horizontally (because the pilot holes are expressed in three decimal places, .199).

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    Administrator Kelly Bramble's Avatar
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    Quote Originally Posted by hogpaw View Post
    Thanks for the response Kelly.

    There is a default tolerance block on the drawing using the method you stated.

    Is this correctly stated (using the default tolerances from your example): The cylinders are allowed to move ±.002 vertically (according to the stated tolerance) and ±.010 horizontally (because the pilot holes are expressed in three decimal places, .199).
    Yes, though I prefer to view the tolerance in this case as ±.002 in any direction. When one zero's on one of the diameters and measures to the other diameter, the orientation is not relevant.

  5. #5
    Thank you for the help.

  6. #6
    Administrator Kelly Bramble's Avatar
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    Ok, I would like to add the following to my post as Mr. Belanger and I have been discussing by sticky mail.

    The ASME Y14.5 standard does not explicitly define that a center line can be a limit dimension, but must be a Basic dimension.

    For those of you reading this and are familiar with ASME Y14.5-2009…

    page 8 paragraph (k)… “A zero basic ..”
    2.1 (page 24), note (e), “in a general tolerance block referring to all dimensions on a drawing….”

    Ok, my position on this issue is that defining that it must be a basic dimension is overlooking that one may have intended the center line to indicate limit dimension, particularly if limit tolerances are all over the engineering drawing or no geometric tolerance is present.

    Moreover if we can define a tolerance block that says “Unless Otherwise Specified” and that definition is .xxx +/- .005 or whatever, clearly it is fair to say that that “zero” as given by the center line should be a limit tolerance.

    To be perfectly correct when applying the current ASME standard, one could apply a .000 dimension to the center line or a note indicating that all dimensions are limit dimensions unless otherwise specified.

    I also think the standard should have worded as follows:

    1.4, paragraph (k)…

    As applicable, a zero limit or basic dimension applies where axes, center planes, or surfaces are shown coincident on a drawing, and applicable limit or geometric tolerances establish the relationship among features.
    And I would say something similar to 2.1.1.4…

    Or something to that effect...

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