"Flatness area" annotation around a mounting hole - necessary if the plane is already flat
"Flatness area" annotation around a mounting hole - necessary if the plane is already flat
(OP)
Is it necessary to annotate specific flatness area (say 20mm dia) around a mounting hole(say 8mm dia) of a support bracket,even if the plane(where hole is located ) is already flat?





RE: "Flatness area" annotation around a mounting hole - necessary if the plane is already flat
If you just got there, removing the annotation will probably get you fired.
Mike Halloran
Pembroke Pines, FL, USA
RE: "Flatness area" annotation around a mounting hole - necessary if the plane is already flat
Is the local flatness tighter than the overal surface flatness?
If the overal surface flatness is specified, and the local flatness was not a refinement then technically I seen no reason the local call out is required.
However, it is worth trying to understand the intent behind why it was added as Mike implies - just in case there is actually a problem that needs fixing even though the fix applied may not be technically appropriate.
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: "Flatness area" annotation around a mounting hole - necessary if the plane is already flat
yes, its necessary to annotate the specific flatness area required for function if the required area is smaller than the entire surface where its located.
lightweight, cheap, strong... pick 2
RE: "Flatness area" annotation around a mounting hole - necessary if the plane is already flat
Then you state that the area around the hole is already flat. That's not a tolerance.
It's like saying, "How accurate does the position of the hole have to be if it's already dimensioned as 3 inches from the edge?"
Every surface must have a flatness tolerance of some kind (unless it's a flexible part, or you just plain don't care if the thing is Gawd-awful warped). Most of the time flatness is indirectly controlled by the size or thickness of the part; that's the Rule #1 idea that Kenat mentioned (if you're using ASME).
So the bottom line is no, an explicit flatness tolerance is not required around that hole, but examine the thickness tolerance and read the notes, title block, etc. to assess what is currently controlling the flatness.
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
http://www.gdtseminars.com