Add to Randy's Monday...

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  • Add to Randy's Monday...

    I wonder : Randy P has a call - POS|fi 1|A|B|C - and we are talking about circular tolerance field. As I see it , we have complete vector (A|B|C), so tolerance field should be spherical. If there is a need for circ field, wouldn't be enough just to call 2D: -A|B- or -D|E-...?

  • #2
    Originally posted by Rob_K View Post
    I wonder : Randy P has a call - POS|fi 1|A|B|C - and we are talking about circular tolerance field. As I see it , we have complete vector (A|B|C), so tolerance field should be spherical. If there is a need for circ field, wouldn't be enough just to call 2D: -A|B- or -D|E-...?
    The simple answer... Does calling just two datums fix all necessary degrees of freedom? If yes, then that is enough. The number of datums called does not dictate whether the tol. field is 2d or 3d.

    Rather, I would say that the feature and/or basic dimensions determine whether the tol. field is 2d or 3d. A sphere for instance could be 3d because it has a very distinct center. A cylinder on the other hand might be a little tougher to apply a 3d tol. field to (depending on part function). In many cases, a screw boss would be measured as a cylinder and it really isn't important where the center of the cylinder is (in 1 out of three directions anyway) but it can be very important where the end of the cylinder is located.

    Given the drawing section Randy posted, I don't think we have enough information to say for sure.

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    • #3
      Ok, I see that. Next, what about Point ? I get lots of demands for locating a point(-A|B|C-). It is not Feature of size ( or is it?). What am I to do : Not to give position or give spherical POS? Waving with Surface Profile usually wouldn't work.

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      • #4
        Single points, report the T axis (T=Total vector deviation along the vector axis of the point) using 1/2 of the tol callout for +/- (ie profile 1.0mm = +/-0.5 for the T axis). For any 3-D point, you absolutely have to have all 3 datums called out or you are not locating the part well enough to check it. If the point has ANY vector other than 0 in each axis direction, you have to have 3-datum callout (ABC or equal).
        sigpic
        Originally posted by AndersI
        I've got one from September 2006 (bug ticket) which has finally been fixed in 2013.

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        • #5
          adding the 3rd datum usually implies perpendicularity
          Which one gets ridden today? MPH vs MPG..tough choice, both are FUN
          sigpic

          Starrett RGDC 4028-24 :alien:
          Demon vintages 3.7, 4.1, 4.2, 4.3, 2009

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