【转帖】ansi y14.5

yang686526

ansi y14.5
i know this may be a basic question but i have one of our designers using a parallel w/in .005 to control a basic dimension of 1.500. my understanding is if he wanted to use a control that covered both parallel and height that a profile tolerance should be used.
i looked in the book and it shows a tolerance zone for parralel but never in relation to a basic dimension.
hope this question is clear enough that someone can help me with this...
thanks
your understanding is correct. to control both parallelism and height , related to a basic dimension, use profile. a parallelism tolerance zone does not relate to a basic dimension.
unless their is some other control on that surface like profile i would have to say the designer is wrong.
here's what i would do... i would call out this surface parallel to datum a to within whatever tolerance is neccessary and then i would add a height dimension to the surface in question and add a tolerance of ±0.005 or whatever is appropriate. i don't think that i would use a profile tolerance in this situation, although i don't think you would really be wrong to do so. lastly, for some reason i can't quite pinpoint, i feel it's neccessary to point out that you can attach the feature control frame to the height dimension on your drawing. it's true that you cannot use a basic dimension with your parallelism callout, but why do you need one? just put a tolerance on it and call it a day.
here are a few links that may be of interest...
thanks
case closed
cheers
parallel tolerance on a surface should not be shown with a basic dimension but with a +/- tolerance. make sure the the tolerance specified is with the tolerance range.
tip - reflecting the surface with profile of a surface is best since it does control the location of the surface, parallelism and also flatness. if you have a profile of a surface tolerance of 0.5 mm from a basic dimension. the 0.5 is the range of a bilateral tolerance. nother can be above or below this value.
basic dimensions are theoretical dimensions and are not tolernaced.
dingy2,
   the thing that is necessary is that we control the position of the surface, as well as its parallelism.  your +/- tolerance achieves this, as does the profile tolerance recommended by caseynick, above.
   i can also do a composite tolerance in which the profile tolerance is 1mm, and the parallel tolerance is 0.05mm for example.  i do this a lot on optical mirror mounts, where the position does not matter much, but the angle is absolutely critical.  
                             jhg
thanks guys i was able to convince him and all is well
the links from gsagolla helped a lot
thanks again