Rule #1 Question - Implied Flatness
Rule #1 Question - Implied Flatness
(OP)
Quick scenario, followed by a question:
A vendor fabricates a large circular panel. It is comprised of two thin aluminum face sheets bonded to aluminum honeycomb core in between. Holes were drilled in this panel, located with positional tolerances. The thickness dimension on the panel is 0.80", +-.1". No explicit flatness is defined. The fabricated part is warped (by a half inch in some places!).
Given that a drawing note indicates to interpret the drawing per ASME Y14.5M-2009;
I realize that there *should* have been an explicit flatness callout on the drawing to avoid confusion, but unfortunately that's water under the bridge at this point.
A vendor fabricates a large circular panel. It is comprised of two thin aluminum face sheets bonded to aluminum honeycomb core in between. Holes were drilled in this panel, located with positional tolerances. The thickness dimension on the panel is 0.80", +-.1". No explicit flatness is defined. The fabricated part is warped (by a half inch in some places!).
Given that a drawing note indicates to interpret the drawing per ASME Y14.5M-2009;
Does Rule #1 apply to the thickness dimension of this panel (i.e. implied flatness of .2" if the part is built to the nominal dimension)?
Or, does the "stock item" argument hold any water here, thereby nullifying Rule #1? The face sheets were called out as .020" 2024-T3C aluminum, and the data sheet for the aluminum core only mentions a thickness tolerance of +-.006".
I realize that there *should* have been an explicit flatness callout on the drawing to avoid confusion, but unfortunately that's water under the bridge at this point.





RE: Rule #1 Question - Implied Flatness
Bill
RE: Rule #1 Question - Implied Flatness
This assembly dimension/tolerance would override the stock dims of the piece parts.
If you don't need tighter than .020 flatness then you don't actually need to add separate flatness tol. However, because places frequently overlook the application of rule 1 to part thickness it can be a good idea to add it as a preventative measure.
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: Rule #1 Question - Implied Flatness
The 'stock' tolerance is to avoid substituting the title block or note dimension tolerance and control for an existing one which may be better or worse.
RE: Rule #1 Question - Implied Flatness
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
RE: Rule #1 Question - Implied Flatness