ANSI Y14.5 6

[thundair]

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

 

[caseynick]

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.

 

[Heckler]

Unless their is some other control on that surface like profile I would have to say the designer is wrong.

 

[MechCT]

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.

 

[gsagolla]

Here are a few links that may be of interest...

GD&T Tips website - Parallelism

GD&T Tips website - Composite Profile

Giuseppe Sagolla
Sr. Mechanical Engineer
Ocean Power Technologies

 

[thundair]

Thanks


case closed

Cheers

 

[dingy2]

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.

 

[drawoh]

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

 

[thundair]

Thanks guys I was able to convince him and all is well
The links from gsagolla helped a lot

Thanks again