GD&T Varying Tolerance Control Over Flat Surface 1

[aeroengr]

Hi,

I have a flat rectangular plate that has a hole on one side with theoretical uniform thickness. I want to be able to control the thickness of the plate around the hole to a tighter tolerance (+/- .004") than the rest of the plate. I thought I could do that through ASME Y14.5 through partial surface as datum features, but I don't know how to dimension the rest of the plate (+/- .015"). Would I have to create two datums on the same surface?

Thanks,

 

[Belanger]

If you want to control thickness of the plate around the hole, I don't see any need for GD&T there. Just use cross-hatching to indicate the imaginary area (perhaps dimension it with a diameter (basic dim). Then give the thickness with the ±.004 but then say something like "shaded area only." The other dimension with the ±.015 can be attached to the general view of the plate, and it will be understood to control the rest of the plate, but for that cross-hatched area.

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

 

[pmarc]

Agree with J-P on this.
It is true that Y14.5 does not give any example of similar case, but for sure there is no need to assign additional datums. If you do it more or less like J-P described, it should be clear enough for any reader.