Ordinate Dimensioning
Ordinate Dimensioning
(OP)
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
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





RE: Ordinate Dimensioning
Just in case: Even if you have one surface and you want only part of it to be used as a datum, you can identify that part with chain line and basic dimension, so it is perfectly clear what is datum and what isn't.
I will be waiting for picture though.
RE: Ordinate Dimensioning
Frank
RE: Ordinate Dimensioning
Y14.5M-1994, pg 172-173, FIG. 6-20 & 6-21.
RE: Ordinate Dimensioning
RE: Ordinate Dimensioning
Frank
RE: Ordinate Dimensioning
RE: Ordinate Dimensioning
Zero basic dimension is implied if your coplanar features are controlled using FCF.
RE: Ordinate Dimensioning
The "inline" is the dimension.
Frank
RE: Ordinate Dimensioning
(k) A zero basic dimension applies where axes, center
planes, or surfaces are shown coincident on a drawing,
and geometric tolerances establish the relationship
among the features. See para. 2.1.1.4.
2.1.1.4 Implied 90° or 0° Basic Angle. Where center
lines and surfaces are depicted on 2D orthographic engineering
drawings intersecting at right angles or parallel
to each other and basic dimensions or geometric tolerances
have been specified, implied 90° or 0° basic angles
are understood to apply. The tolerance on the feature
associated with these implied 90° or 0° basic angles is
provided by feature control frames that govern the
location, orientation, profile, or runout of features. See
paras. 1.4(j) and (k).
If I'm reading that correctly then would you agree my dim. scheme below is valid?
RE: Ordinate Dimensioning
you were right, at the time I didn't think that by showing the relationship through tolerancing I am able to use implied 0°. I saw it as two different issues.
What if I only wanted one of those surfaces to be the datum, what would my picture look like then?
Thanks,
Pete
RE: Ordinate Dimensioning
Probably a target area would be best (a chain line) on the one you want or separate leaders as shown in the standard, I referenced before, again, someone will want to know how close the other surface has to be.
Frank
RE: Ordinate Dimensioning
Frank
RE: Ordinate Dimensioning
An option I use a lot is to apply a separate datum to each of the two faces.
In your diagram, let's assume that ordinate zero is your primary datum. My FCFs look like...
|pos|Ø0.2|A-B|C|D|
This shows explicitly that both your end surfaces are primary datums.
RE: Ordinate Dimensioning
Very true, I was the one doing the short cutting here.
Frank
RE: Ordinate Dimensioning
RE: Ordinate Dimensioning
If ASME Y14.5M-1994 then I think you'd have to use surface profile to indicate how 'co-planar' they are. Or maybe the dual datum approach.
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: Ordinate Dimensioning
Matt Lorono, CSWP
Product Definition Specialist, DS SolidWorks Corp
Personal sites:
Lorono's SolidWorks Resources & SolidWorks Legion
RE: Ordinate Dimensioning
Don't think "continuous feature" applies because that surface isn't a feature of size.
RE: Ordinate Dimensioning
Frank
RE: Ordinate Dimensioning
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
www.d3w-engineering.com
RE: Ordinate Dimensioning
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).
RE: Ordinate Dimensioning
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
RE: Ordinate Dimensioning
If you need all four colpanar surfaces to be the primary datum, then a "4 PLCS." or "4X" "note should work fine.