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using feature control on un finished surface

using feature control on un finished surface

using feature control on un finished surface

hello - hope all is well - i was called out today during a drawing review by 2 people that i work w/ about using datum features on an unfinished surface - i was told in no uncertain terms never to do that again because "they were taught not to do that" - case in point i used the feature controls on a welded piece that was 3 flats one that made up the bottom plate & 2 side plates that when welded together formed a u-shape - in the past our over seas manufacturing plant has had trouble keeping the side plates perpendicular to the bottom plate - we had decided in the past to use feature control to keep this from happening - now today i was told this was wrong - the plates were not held to a tight tolerance - the bottom plate was "a" & the inside of the 2 side plates were each held perpendicular to the "a" datum within .03 (which i thought was more then correct) - i just need a verification about using feature controls on unfinished surfaces - after i went back to my gd&t book i saw nothing about this - any help would be greatly appreciated - tired of getting beat up over the drawings i make especially since our company & department have no standards to work by except "what other people have been taught" - thank you

RE: using feature control on un finished surface


Can you show us a drawing?

I see no problems using unfinished surfaces as datum features. I see big problems using finished surfaces as datum features, because at some point in the fabrication, they are not finished yet.

A possible problem with your datum A feature is that it is not flat. Read up on datum targets.


RE: using feature control on un finished surface


We use as-fabricated surfaces as datums. We apply datum targets to tell the shop/QA where to contact the surface to establish the datum (to align the part to machine tool travel). Just a suggestion.

Certified Sr. GD&T Professional

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