Hole location dimension when TOP is used

[87]

I have attached drawing having following interpretations when GD&T TOP position tolerance used.
Pic 1: All Holes are dimension from DRF
Pic 2: Holes are (Y axis) dimensioned from hole to hole. (Middle and upper hole Y axis dimensions are not from DRF)
Explain how each interpretation works. Inspection would consider both interpretations are same?

 

[3DDave]

Files with odd characters, like "&" don't download. Not sure why they can be uploaded.

 

[87]

Ok, i have uploaded new file

 

[3DDave]

Yes. The interpretations are the same.

 

[87]

Question is why the hole to hole location dimension in ASME Y14.5 doc. pics. Inspection will not consider the way its dimension?

 

[CheckerHater]

The Basic dimensions are theoretically exact "perfect" dimensions.
Thus they are not subject to tolerance accumulation.
Think of a drawing with basic dimensions and FCFs as description of a gauge you have to build to check the part.
No matter how you dimension it, the pins will be located in exactly the same places.
I hope it helps.

"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future

 

[mkcski]

Also: consideration must be given for parts with symmetrical features so you are sure to always use the same features to establish the referance frame. For you drawing; which side is B - left or right - hard to tell if the part is in your hand. Mark the part so there is not doubt.

Certified Sr. GD&T Professional

 

[powerhound]

The position callout says the holes are located from the datum reference frame A, B, C. Where those datums intersect is the origin of measurement for all the holes. Your inspection department should really understand this. Are you saying they don't?

John Acosta, GDTP Senior Level
Manufacturing Engineering Tech

 

[Tunalover]

Yes, I agree. The great thing about basic dimensions is that it is largely immaterial how they are done as long as the positions ultimately originate from the datum references. My preference though is to do functional dimensioning so the reader better understands the part function.

One minor point w/r/to the drawing views. Drafting protocol uses arrowheads only when the arrow point is touching an object line or a boundary line. If you want to call out a datum on a surface you should use the "dot" terminus or "integral" terminus, for example, when the terminus is not touching an object line or boundary line. Just my 2¢.

H. Bruce Jackson
ElectroMechanical Product Development
UMD 1984
UCF 1993