Help with Flatness on long part 1

[MadMango]

I have a molded part that has X-Y and Y-Z flatness, where Y is close to the middle of the part, and X and Z are the opposite ends. Can I (or how do I) call out a X-Z "overall" Flatness as well?

"Art without engineering is dreaming; Engineering without art is calculating."

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[Belanger]

Use a separate feature control frame that points to the whole surface without a designation for X, Y, or Z points. If that might still be unclear, you can add a note under the feature control frame saying "entire surface."

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

 

[BillPSU]

It would depend on the usage of the part. Flatness is one of the toughest dimensions to maintain on a large part. On a molded part there may be droop caused by over temperature in the part. The ejector pin locations may have to be excluded from the tolerance.

It comes down to how much out of flat can the design accept and still function.

Bill

 

[MadMango]

We know there will be different cooling rates due to material thickness and features, as half is uniform thickness but bowl-shaped and the other half has optical pillows that are about 3X material thickness in some areas. We are trying to give some wiggle room for the X-Y area and stress the importance of Y-Z related to sealing sirfaces. I decided to use another FCF with X-Z under it to hopefully reduce the confusion.

"Art without engineering is dreaming; Engineering without art is calculating."

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