Datum/Ordinate Dimensioning in the same view on a drawing

[rdpostak]

Is it okay per Y14.5 to have both dimensioning schemes in the same view?

Richard D. Postak
Aerospace Mechanical Designer
Schafer Corporation

 

[ewh]

I think KENAT pointed you in the right direction in your other post.

"Know the rules well, so you can break them effectively."
-Dalai Lama XIV

 

[rdpostak]

ewh,

Thanks for the confirmation.

 

[drawoh]

rdpostak,

My test for your drawing would be "Does it specify what you will accept from the vendor?"

Your drawing needs to be clear. You don't want redundant dimensions. You do want to dimension everything. To me, datum versus ordinate dimensioning is a detail.

--
JHG

 

[rdpostak]

drawoh,

So are you saying you prefer ordinate over datum?

 

[drawoh]

rdpostak,

For me, ordinate dimensions from the datum are the way to go, most of the time.

--
JHG

 

[rdpostak]

drawoh,

Are you in the automotive industy?

 

[drawoh]

rdpostak,

No, I am not.

--
JHG

 

[pmarc]

Any chance to see an example showing the problem?

 

[rdpostak]

pmarc,

No there isn't, sorry. It is company confidential.


Richard D. Postak
Aerospace Mechanical Designer
Schafer Corporation
richard.postak@schafercorp.com

 

[pmarc]

Okay, so let me try this way:
Assuming you have access to Y14.5-2009, are you able to take a figure from it and explain by words the scenario your question is about?

 

[rdpostak]

pmarc,

Okay, let me ask my question this a way. Would it be considered the norm to do one way or the other versus both in the same view?

Richard D. Postak
Aerospace Mechanical Designer
Schafer Corporation

 

[pmarc]

The reason I have been asking you for a graphical example is that I would first like to understand what you mean by "ordinate" vs. "datum" dimensioning.
My understanding of ordinate dimensioning is that there is always an origin defined which is a sort of a datum. So actually, as drawoh pointed out, ordinate dimensioning is datum dimensioning.

 

[JNieman]

I don't pretend to speak for many, but I've often seen a mix. Typically the ordinate dimensions will be the more precise features of a part, or things that would create a bird's nest of lines to linearly-dimension. Then you might have less-precise objects dimensions directly, such as cutouts, overall sizes (if non-critical), etc. Then you might have a hole table off to the side which is third 'method' of dimensioning.

Context for me is mostly aerospace and general tooling.

 

[drawoh]

rdpostak,

You are going to have to show us an example. Nowadays, most of the time, I dimension the centre of a pitch circle from the datum, then show the diameter and spacing of the pitch circle. I used to systematically show each hole as an ordinate dimension. An important issue that is separate from ASME Y14.5 is that ordinate dimensioning can dimension many, many holes clearly and readably. At some point, you have to go to hole tables.

ASME Y14.5-2009 is not a procedure. It is a language. It shows ordinate dimensioning as an option, along with a lot of other options. You have a toolkit for applying dimensions to your view. What will make it clear?



--
JHG