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

 

[CheckerHater]

Something happened to your picture.
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.

 

[fsincox]

Either option can be done, you will just need to make it clear which you intend to be the case. Targeting could be done, if a simpler method is not clear enough. For the "0" line if you extend it accross to both surfaces it is implied "inline". We still have the option of notes like 2X, (2) SURFACES and if applicable "CONTINUOUS FEATURE", "COMMON ZONE" or a COPLANARITY will also do it.
Frank

 

[fsincox]

The ASME Y14.5 standard shows a few examples of options:
Y14.5M-1994, pg 172-173, FIG. 6-20 & 6-21.

 

[PRuggiero]

Sorry forgot to click the last button... The question is really more dimension based than tolerance.

 

[fsincox]

I had a feeling that you were trying to stay away from the GD&T solutions. Extending the line across or noting "2X" works for me, the zeros in different places, not so much, and no indication at all, I don't like either. The issue of tolerances will have to be dealt with whether you like it or not, though.
Frank

 

[PRuggiero]

fsincox, I agree.. Wasn't trying to ignore those but that is "well" defined in the Y14.5 on how to achieve it. What I can't find is how to dimension it. I'm trying to find a document that shows you how to dimension it properly. I agree with either 2x or the dashed line, but what is really correct? Even if you use the Fig 4-23 (Y14.5 -2009) you still have to dimension both surfaces, no?

 

[CheckerHater]

You may want to take a look at Fig.8-15 (Y14.5-2009)
Zero basic dimension is implied if your coplanar features are controlled using FCF.

 

[fsincox]

OK, I was just making the point that you will have to deal with the tolerance question sooner or later, so why not build it in and take avantage of it.
The "inline" is the dimension.
Frank

 

[PRuggiero]

Yep, seen that figure before, but it doesn't show any dimensions at all. So it looks like section 1.4k describes what i'm talking about:

(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?

 

[PRuggiero]

fsincox,

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

 

[fsincox]

I still think you could have shown "inline" but someone will eventually want to know: "how close".
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

 

[fsincox]

"and geomentric tolerances establish the relationship between features".
Frank

 

[drawoh]

PRuggiero,

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.

JHG

 

[fsincox]

drawoh,
Very true, I was the one doing the short cutting here.
Frank

 

[PRuggiero]

drawoh, yep i've done it that way too. If you only have the one "0" dimension you would still need some GD&T relationship between A and B for the implied 0° basic dimension to apply.

 

[KENAT]

Not familiar with 2009 edition.

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.

Posting guidelines faq731-376

http://eng-tips.com/market.cfm?

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[fcsuper]

You should consider using the "CONTINUOUS FEATURE" option with your largest exmaple.

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

 

[PRuggiero]

fcsuper,

Don't think "continuous feature" applies because that surface isn't a feature of size.

 

[fsincox]

The ASME really screwed that up; "COMMON ZONE" should have just been accepted by them in the interest of commonality. Apparently, there is an example in 2009 that shows it used on a non-continuous surface like you have, so at best, they are inconsistent in their own logic.
Frank