We have a plate that has one face t

[Matt Fromhold]

We have a plate that has one face that is marked as a datum surface. We have features that are called out dimensionally off of this surface. I understand that 3 points can define a plane. Can we just machine 3 areas on that surface and pull the other features off of those or does it mean the whole surface? Thank you

 

[TheTick]

Yes you can. If you're using GD&T you can designate the spotfaces as targets for your datum plane.

 

[drawoh]

Matt Fromhold,

The whole face is your datum feature. The ASME[ ]Y14.5 standard explains how to interpret non[‑]flat surfaces. If lack of flatness is a problem, you may have to fly cut the face. Your next choice is to get your designer/drafters to implement TheTick's suggestion.

Strictly speaking, you don't need spotfaces. You can just specify on your drawings where the datum targets are. The spotfaces will make everything more obvious and explicit.

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JHG