【转帖】please suggest tolerance scheme

yang686526

please suggest tolerance scheme.
hello everyone,
i have the following situation and i would appreciate if  someone can suggest a tolerancing scheme for the following group of holes: i have three holes. the circular outside boundary of the part is not important. the three holes are inline. the top and bottom holes have a tight diameter tolerance. the center hole does not. the center hole is located midway between the top and bottom holes. the center hole can drift a lot perpendicularly from the plane formed by the top and bottom holes. however the position of the center hole to the midpoint must be tight (see attached sketch).
i am thinking of making the one of the sides of the part where the holes are datum a. then, making the top and bottom holes a single datum. so, i apply a position tolerance to these two holes relative to datum a and make them datum b. how do i use tp or symmetry to dimension the center hole and assign the requirement described above?
thank you.
jv
see fig 5.41 on p. 139 in the standard. this is how you position bidirectionally.
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hi jv1
i agree with powerhound.
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