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Thread: Help me understand this please:

  1. #1
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    Question Help me understand this please:

    The attached example is from an introduction to blueprint reading course. It has the position of the thru hole axis designated as within a .8 tol zone relative to datum A which is a plane perpendicular to the hole axis. is this essentially just controlling the perpendicularity of the axis? If so, would it have been better to use a perpendcularity control explicitly?
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  2. #2
    Administrator Kelly Bramble's Avatar
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    What is the dimensioning and tolerancing standard this drawing is using? Also, who's basic training material is this?
    Tell me and I forget. Teach me and I remember. Involve me and I learn.

  3. #3
    Same example is discussed somewhere else: "position’s main job is to control location — meaning that it involves a distance — and perpendicularity often comes along as part of that position control. Since the large hole given above is already distanced from the edges by plus/minus dimensions, the geometric tolerancing has nothing to do with location. The only relationship that the large hole has with datum A is one of orientation. Therefore, an orientation symbol must be used..." Perpendicularity symbol "is the correct way to identify this hole, since the hole itself now becomes the datum feature for other features to locate back to. That said, there are no GD&T police that will haul you to jail if you insist on using the position symbol. But recall that the purpose of geometric tolerancing is to use a standardized language to express the design requirements. So it’s best to stick with the proper terms and symbols if you want to minimize confusion when expressing your requirements!".

  4. #4
    Administrator Kelly Bramble's Avatar
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    Two thumbs up. ASME or even the older ANSI standards this holds true however, ISO 1101 allows position to be used exclusively for orientation. In fact, ISO even allows position to be used for features without size, like a plane surface. The resultant tolerance boundaries are most like (exact) a profile of a surface.

    Quote Originally Posted by newone View Post
    Same example is discussed somewhere else: "position’s main job is to control location — meaning that it involves a distance — and perpendicularity often comes along as part of that position control. Since the large hole given above is already distanced from the edges by plus/minus dimensions, the geometric tolerancing has nothing to do with location. The only relationship that the large hole has with datum A is one of orientation. Therefore, an orientation symbol must be used..." Perpendicularity symbol "is the correct way to identify this hole, since the hole itself now becomes the datum feature for other features to locate back to. That said, there are no GD&T police that will haul you to jail if you insist on using the position symbol. But recall that the purpose of geometric tolerancing is to use a standardized language to express the design requirements. So it’s best to stick with the proper terms and symbols if you want to minimize confusion when expressing your requirements!".
    Tell me and I forget. Teach me and I remember. Involve me and I learn.

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