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Ordinate Dimensioning

Ordinate Dimensioning

Ordinate Dimensioning

(OP)
Are tolerances applied to the origin in ordinate dimensioning?

RE: Ordinate Dimensioning

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
Profile Services  www.profileservices.ca
TecEase, Inc.  www.tec-ease.com

RE: Ordinate Dimensioning

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

RE: Ordinate Dimensioning

(OP)
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!

RE: Ordinate Dimensioning

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
Profile Services  www.profileservices.ca
TecEase, Inc.  www.tec-ease.com

RE: Ordinate Dimensioning

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.

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RE: Ordinate Dimensioning

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.  

RE: Ordinate Dimensioning

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

RE: Ordinate Dimensioning

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
Engineering Technician
Inventor 2010
Mastercam X5
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II

RE: Ordinate Dimensioning

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

RE: Ordinate Dimensioning

(OP)
Agreed.

RE: Ordinate Dimensioning

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
 

RE: Ordinate Dimensioning

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...

RE: Ordinate Dimensioning

lol

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

RE: Ordinate Dimensioning

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

RE: Ordinate Dimensioning

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

RE: Ordinate Dimensioning

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

RE: Ordinate Dimensioning

Ha ha  -- I just picked Chicago randomly; I didn't know they have an actual datum marker!

I am east of Chicago.  Don't try to track me down, guys.  I won't be home.

And I certainly agree that this whole thread is an illstration of why GD&T should be used.  I don't want to appear to defend a drawing practice that might be confusing.

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

RE: Ordinate Dimensioning

Quote (MM2011):


Are tolerances applied to the origin in ordinate dimensioning?

   I tried to do this once, and everyone laughed at me.  I wanted to apply a ± tolerance to a hole at my zero position.

   Once again, GD&T positional tolerances solve the problem.

   
 

               JHG

RE: Ordinate Dimensioning

Quote:

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!).  

It is spelled out in the standard.  Ordinate dimension isn't called "ordinate" in Y14.5.  It's called "Coordinate Dimensioning without dimension line".  The 0 is only the baseline for the oridnate set.  It is treated the same as baseline dimensioning or any other coordinate dimensioning scheme.  It is not the same as the dimension origin symbol.  Dimension origin symbol is used to specify that a tolerance is taken from on feature and not the other.

ISO used the same symbol with "running" dimensions, but it makes no statement (at least that I can find) that states the tolerance shall be taken from baseline only.

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

RE: Ordinate Dimensioning

The tolerance for an "origin" in an ordinance scheme is dictated by the tolerance of the overall length and width of the part in relation to whatever features are between.

A hole 6" off the origin ±.005" is no different from an origin point off the hole ±.005". If you want to consider it as the origin has a tolerance in relation to the hole (as opposed to the other way around) that's very strange, but go for it. Just watch out for stacking tolerances.

RE: Ordinate Dimensioning

Thanks, Matt.  I didn't have the standard in front of me at the time.  This is all well and good, but the OP's question was about where the tolerance resides.  The standard doesn't spell that part of it out.  So I guess we do have to treat it as if it were traditional dimension lines (arrowhead dimensioning).

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

RE: Ordinate Dimensioning

What is the tolerance of half of a dimension? A dimension measures betwwen two points. The origin is only one of those points.

RE: Ordinate Dimensioning

Tick is right.  The only way to give a tolerance to the "starting point" of an ordinate dim is to have a higher level coordinate system with its own "untoleranced" starting point.  Everything is relative.  I think Eistein said that. :)

The Y14.5 is very clear about this.  Ordinate dims are nothing more than coordinate dimensions that don't have dimension lines on the drawing.  They are treated the same as any other coordinate dimensions.  The tolerance is applied to the dimension itself; the feature at either end can vary within that tolerance.

Even the Origin Symbol doesn't tolerance one end or the other.  It simply applies the tolerance variation to the far end only. The baseline is treated as sort of a datum (datum rules from GD&T don't apply to it, but it is still the reference from which the dim originates, rather than having no preference if the symbol isn't used).

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

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