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Thread: Straightness or Profile of a line/surface?

  1. #1
    Associate Engineer
    Join Date
    Feb 2015

    Straightness or Profile of a line/surface?

    I would like peoples opinion regarding what is the better way to call out a GD&T feature control frame. I'm going to use a basic description. If I have a piece of steel that is rectangular in a plan view but curved in a side view and want to control its bow/straightness in the plan view what would u say is the proper way? Should I use straightness or profile of a line/surface?

  2. #2
    Administrator Kelly Bramble's Avatar
    Join Date
    Feb 2011
    Bold Springs, GA
    Straightness and profile of a line geometric tolerances require a tolerance line orientation. The orientation for Straightness and Profile of Line tolerance boundaries are normally defined by attaching the feature control frame leader to the surface in the drawing view that shows the surface true profile.

    By attaching the leader of the feature control in the plan view as you described, Straightness and Profile specification will not define the orientation of the tolerance lines with respect the curved surface profile.

    Profile of a Surface is your only option to control form and size of the curved surface from the plan view. You would you a "dot" leader end instead of an arrow to indicate the curved surface from the plan view.

    You could tolerance control the surface curvature in the side view with a limits of size, limits of size with a straightness refinement as well a profile of line tolerance.

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