Ordinate Dimensioning

[MM2011]

Are tolerances applied to the origin in ordinate dimensioning?

 

[MechNorth]

The usual questions. 1) which GD&T standard? 2) is the dimension basic or directly toleranced? 3) if directly toleranced, is there a dimension origin symbol on the zero-position?

Jim Sykes, P.Eng, GDTP-S
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[ctopher]

The origin is 0,0.
Wouldn't that be like telling the machine the starting point has a tolerance?

Chris
SolidWorks 10 SP5.0
ctopher's home
SolidWorks Legion

 

[MM2011]

The dimension is directly toleranced, based on # of decimal places (2 is +/- 0.01", 3 is +/- 0.005" and 4 is +/-0.0005"), and is the basis of the question. For instance, we typically design tooling with stacked plates with common holes. As a method of checking the prints, we will use the same origin for all the plates. That origin may or may not coincide with a feature. Does the # of decimal places (ergo the tolerance) apply to the origin, or is it absolute? Thanks!

 

[MechNorth]

the problem is that there is nothing in Y14.5 indicating that the ordinate-zero is the origin of measurement, so you can measure from the dimensioned feature to the zero-feature.

Jim Sykes, P.Eng, GDTP-S
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[KENAT]

While you don't say what drawing standard you use, I can't point you a section of ASME Y14.5M-1994 that I know of which would explicitly answer this. 1.9.2 doesn't go into that much detail.

However, the '0' is analogous to a datum in many respects.

Also just logically, if it has a tolerance, then using that dimension system seems almost unfeasible.

Posting guidelines faq731-376

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

 

[pmarc]

As long as there is no origin symbol shown instead of one arrow of typical coordinate dimension with +/- tolerance, such dimension should not be tied to anything. It is a size requirement not constrained to any other external features.

I do not think the answer for this question depends on GD&T standard used.

 

[MM2011]

It seems more a matter of semantics than anything else. I might as well make the origin "0" with no decimal places.

 

[powerhound]

Just as a matter of straightforward common sense, it seems to me that the origin is the starting point. It should not be a matter of an origin measuring a certain distance from a feature but rather a feature measuring a distance from the origin, regardless of which plate you are checking. Without overcomplicating the issue, the origin should always be the 0,0 point from which to measure the other features.

Powerhound, GDTP T-0419
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[Belanger]

I agree with Powerhound. If I say that I am 200 miles outside of Chicago, give or take a few miles, wouldn't you think of those few extra miles as the "tolerance" on my house, and not where Chicago is?

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

 

[MM2011]

Agreed.

 

[fsincox]

I am with powerhound, the origin can be chosen for convienence all the easier with GD&T. Auto companies, ship and aircraft companies like to choose origins that are not even on the part but may reference a global assembly origin. With GD&T you can establish features on the part that are important mating features and then reference back with basic dimensions to the origin and dimension other features basic from there. The FCF does all the "heavy lifting" relating the features to their respective datum framework. since the dimensioning scheme leaves little clue.
Frank

 

[fcsuper]

0 is not a dimension by itself. It is the origin of the dimension. The tolerence applies to the dimension, not the origin.

Matt Lorono, CSWP
Product Definition Specialist, DS SolidWorks Corp
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[CheckerHater]

Sorry, but I just couldn't resist:

JP,

If the distance from Chicago to your home is 200+/-5 miles, then distance from your home to Chicago is...?

Checkers...

 

[ewh]

"Good to know you got shoes to wear when you find the floor." - [small]Robert Hunter[/small]

 

[Belanger]

Wait, CheckerHater... we are talking about ordinate dimensioning, which has a clearly delineated zero point (Chicago in my analogy).

Your question turns it around, so you are changing the zero point to be my house. So it's not the same in terms of how the tolerance is envisioned. The numerical distance is the same (duh), but the phrasing of the question has implications!

I think that using ordinate dimensioning is seen as equivalent to the dimension origin symbol. Admittedly, that's not spelled out in the standard (and I'm usually the hardliner about following the letter of the law!).

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

 

[Belanger]

In case anyone cares, my house is actually 301 miles from Chicago, according to Google maps.

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

 

[CheckerHater]

East or West?

Eather way should use this:

http://en.wikipedia.org/wiki/File:Chicago_City_Datum.jpg

Actually this thread is pretty good example of confusion that happens when you don't use GD&T

 

[CheckerHater]

East or West?

Eather way should use this:

http://en.wikipedia.org/wiki/File:Chicago_City_Datum.jpg

Actually this thread is a good example of confusion that happens when not using GD&T.

 

[CheckerHater]

Sorry for double-posting, got lost in buttons. Way over my 40 hrs this week