Ordinate Dimensioning

[PRuggiero]

Guys,

I have what I think is a simple question but Google couldn't even answer it...

If one is using ordinate dimensioning and you have multiple surfaces that are co-planer and represent the "0", how do you show that on the drawing.

Perhaps more info is needed... I know if I wanted both of them to be datums I could control the surfaces through a profile and put "2 surfaces" down. What happens if I only wanted one to be the datum? Either way you have to dimension both surfaces, no?

I attached a simple picture which I don't think is correct with respect to how the co planer surfaces are dimensioned.

Thanks,
Pete

 

[DeanD3W]

CF can be applied to planar surfaces... The wording of Y14.5-2009 3.3.23 and also figure 7-45 provide sufficient (though not as good as it should be) justification. With CF defining the the coplanar surfaces as one feature, flatness would impose one tolerance zone upon them, so it would control their form and coplanarity. A bit more intuitive control compared to profile may be the advantage of this approach...

If you prefer to wait for the next version of Y14.5 for what I hope will be more clear and explicit justification for applying CF to planar surfaces then profile will still do the job, of course.

Clearly identifying both surfaces as a datum feature or features is important, as others have pointed out.

Dean

http://www.d3w-engineering.com

 

[PRuggiero]

ah, it does look to be that way... Definitely could use some clarification like you guys say.

Do you think "continuous feature" is common enough that you won't scare away people quoting for machine shops... Being able to accomplish something in multiple ways one has to wonder which is the best (gets the point across, costs the less, etc).

 

[fcsuper]

My experience, well established machine shops know GD&T better than engineers.

The test to see if a shop knows GD&T is to always do competitive quoting. If a shop comes in high, ask why. If they say "GD&T", tell them good bye (and not just because of the high quote).

Matt Lorono, CSWP
Product Definition Specialist, DS SolidWorks Corp
Personal sites:
Lorono's SolidWorks Resources & SolidWorks Legion

 

[tz101]

If you only wanted one of the coplanar surfaces to be your primary datum, then I would label the surfaces "A", "B", "C" etc. in the plan view and the datum callout frame would specify "Surface A", "Surface B" or whichever feature you desire to be the primary datum.

If you need all four colpanar surfaces to be the primary datum, then a "4 PLCS." or "4X" "note should work fine.