Profile of a surface for dimensional tolerance

[RacefanJTD]

Good Morning.
I am working with a customer drawing (see attached PDF)and I am not sure of the way they are using this feature to control tolerance. In this example they claim that the entire part is held to the profile of a surface tolerance, which would be in this case ±2.5mm. I have a few issue's with this but because I deal with this so little I am not sure.
To use this feature wouldnt all of the dimensions have to be basic?
Is this a valid way to measure a distance feature from a datum? Practical?
Does the tolerance block imply ± 2.5, or a range of 5, say if nominal was 30 would a range of 29 to 33.5 be OK.
Are there any flaw's with this control?

 

[RacefanJTD]

I did forget to mention that the next line under the feature control frame states that Dimensions w/o tolerance are Reference.

 

[ewh]

Seems like a typo to me. ALL of those untoleranced dimensions are reference? Are these features defined elsewhere WITH tolerances?

Believe it if you need it or leave it if you dare. - [small]Robert Hunter[/small]

 

[dgallup]

Yes, I think they should all be basic and I don't think there are enough.

 

[drawoh]

RacefanJTD,

"UNLESS OTHERWISE SPECIFIED..."

Maybe it is not a standards compliant drawing. I think the intent is pretty clear.

JHG

 

[dingy2]

You are correct that all dimensions shown on the drawing should be basic but, frankly, I really dislike this way of applying GD&T.

GD&T should apply on features where there is a function and relationship within the part or to the mating part. I don't think that this applies here but it easy for the Design to apply.

A 5 mm profile means a +/- 2.5 mm from the basic dimension or theoretical dimension.

Dave D.

http://www.qmsi.ca

 

[BARM]

Looks like typical drawing information for the automotive industry. You've gotta remember that it's only surface tolerance that they've given you. Any holes or fastener locations would have a different location tolerance.

Also, you haven't supplied us with the complete drawing so I can't commit to a total comment but typically the dimensions shown would be basic and should be stated as such in the title block.



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