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Flatness : With convex & concave error specification?

Flatness : With convex & concave error specification?

Flatness : With convex & concave error specification?

(OP)
Hi All,
I have one question, I have an extruded square part. The bottom surface where it makes contact with its counter part, is controlled with a flatness of 2mm.
I have a design requirement for flatness, the convex error allowed is only 0.5mmm. it can have concave error upto 1.5mm. How do I specify this requiremnt on drawing?

Please share your thoughts.

RE: Flatness : With convex & concave error specification?

Similar situation was discussed before: thread1103-348583: Straightness Tolerance concave vs convex?

The questions are:
Are you simply interested in by-lateral tolerance zone, or trying to achieve "no-reversal" concave/convex shapes?
Are you in ASME or ISO world?

ASME now allows more tricks applied to tolerance zone, like actual sketching the shape of the zone if necessary.

Unfortunately, as mentioned thread concluded, you may still have to resort to verbal note.

RE: Flatness : With convex & concave error specification?

Right -- a note might be the only way.

Even with all the tricks of profile such as unilateral, all that does is tell you on which side of nominal the tolerance zone lies. Within that unilateral zone, however, the surface could still be either concave or convex.

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

RE: Flatness : With convex & concave error specification?

That's what I was talking about.

Even with "non-uniform" trick (see here: http://files.engineering.com/getfile.aspx?folder=5...) the tolerance zone will allow for smaller reversals.

On the other hand, if you are not worried about small details, and only want bi-lateral tolerance zone, it's do-able.

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