Gd & T for sheetmetal 1

[ashivu123]

Datum qualifier (flatness) is required for sheet metal parts?Part is having 3 flanges 90 deg, bottom face is Datum A and two other surfaces are datum B & C. Datum A surface having flatness of .060. is flatness applied to surface or sheet thickness? shee thick is .032 inch.

 

[JNieman]

Flatness applies only to the face the Feature Control Frame indicates. If they want flatness to apply to both sides, they'd have to apply specifically as such.

_________________________________________
NX8.0, Solidworks 2014, AutoCAD, Enovia V5

 

[ctopher]

Call a sheet metal company.
I think a flatness .060 for .032 thick may be a little tough. But, there are processes to control that.
Link

Chris, CSWA
SolidWorks '15
SolidWorks Legion

 

[drawoh]

ashivu123,

Flatness and datums are two separate things. Datum[ ]A is the three points sticking furthest down from the surface. Sheet metal is flexible, so you should read up on Free State Variation. You can specify how your part is to be clamped to determine datum[ ]A.

You apply a flatness specification to a surface, not a thickness. Given the lack of rigidity of .032"[ ]metal, is flatness a useful concept. Your part will bend to the shape of whatever it is clamped to.



--
JHG

 

[3DDave]

For 2009, flatness can also apply to a thickness, though why is a mystery.

 

[Belanger]

Dave, before 2009 that idea was accomplished with straightness (for a center plane). Did you prefer that method?

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

 

[3DDave]

That straightness is weak was not a reason to double down by extending flatness.

The 2009 standard covers the same concept two ways: the explicit use of the Independency symbol and by the exemption from straightness and flatness in 2.7.1 a (the same paragraph that invokes a 'true geometric form' concept that is undefined and is similar to the 'true geometric counterpart' listed as being replaced in the '2009 by the term 'datum feature simulator')

What it does poorly is explain how using RFS on the flatness of a mid plane should be handled; the boundary is not a fixed Go-No Go sort, but the illustration treats the part as if it is, as if there is no difference from the MMC case.