Datum Reference Frames fo Composite Tolerences

[timverisurf]

Question: Can you have the following callout? First tier - Profile of a surface w/in .030 to A-B-C. Second tier - Profile of a line w/in .010 to A-B-C.

I believe that the second tierwould cancel out the top. Please give me your thoughts.

Tim Martinez
Anaheim, Ca

 

[vigildesign]

Since you are calling out datums on the profile of a line tolerance, you are overriding the profile of a surface callout. With datums, the entire surface is being controlled by location (position) to the specified datums by the profile of a line callout. Without datums, profile tolerances act as form controls. You could omit the datums on the profile of a line callout and have a valid callout.

Marcelino Vigil
GDTP T-0377

 

[timverisurf]

What we have is an extrusion shape. The entire surface needs to be w/in .030 to A-B-C and each section cut line of inspection points needs to be w/in .010 holding the same datum orientation but not locked to position. How would this be called out?

Profile of surface w/in .030 to A-B-C
Profile of a line w/in .010 to ?

Which datums do we need to use to lock the rotation but allow it to move positionally?

Thanks in advance,

Tim Martinez

 

[dingy2]

Profile of a surface is three dimensional while profile of a line is two dimensional.

I can see the possibility of profile of a surface to A,B & C which controls the shape and location of the surface and is usually perpendicular to datum A.

Profile of a line is two dimensional and controls the shape of the shape and the location of the feature at its edge. One usually should never see profile of a line referencing three datums.

Yes, one could see profile of a surface .030 to A,B and C while the second level is profile of a line .010 (component of profile of a surface) to B & C. (not datum A).



Dave D.

http://www.qmsi.ca

 

[powerhound]

Tim,
What you are describing sounds like exactly what this GD&T tip addresses. Go to this link and study what it says and it would be a good idea to bookmark the link too. There's a lot of good information there. From what I can see, there is no need for a "Profile of a line" specification. Just refining the lower tier as required while still using the Profile of a surface callout.

http://www.tec-ease.com/tips/may-03.htm

Powerhound
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