Ordinate dimensions and Geometric tolerancing

[TLorich]

Is there a way to have the geometric tolerancing box display correctly in 2008? I am using vertical ordinate dimensions in a drawing. When I try to add a geometric tolerance to these dimensions it does not display correctly. If I select the dimension first and select the GD&T button, the tolerance display ends up cover half of my dimension. If I select the face (or line) first and then place the tolerance directly vertical, the leader line for the tolerance box appears right through the middle of my dimension.

 

[TheTick]

????

GDT gets added to features, not dimensions (except feature size dims). What am I missing?

 

[gurujeff33]

GDT gets added to dims all the time. true position of holes is on the dim, parallel and perpendicularity of bores threads etc all to dims.

yes there are quite a few that are done to features as well.

both are widely used

 

[TheTick]

GDT gets added to dims that indicate feature size. Ordinate dims do not indicate feature size.

 

[gurujeff33]

GDT does not always indicate feature size.

True position is a GDT that indicates position not feature size.

Thus it would be attached to a dimension and not a feature.

 

[TheTick]

I didn't say GDT indicates only size. I've written only a few short sentences and I do not see that statement in any of them.

If you attached a true position to a dimension, it would be a dimension indicating a feature's size, such as a hole diameter or slot width. It would not be attached to a dimension indicating the hole's position, such as an ordinate dimension.

 

[fcsuper]

Eitherway, it isn't appropriate to attach GeoTols to ordinate dims themselves. Positional attaches to the feature, either through a feature size dimension or by direct application (same thing anyway). This will force ordinate dims to be Basic, but not themselves attached too.

Is this a case where the GeoTol happens to be one of the surfaces with an ordinate dim to it? If so, this is coincidence is not design intent. The GeoTol should be attached to the surface itself, not the incidental dimension to that surface.

For example, if a positional was applied to one ordinate of a feature, then how would someone interpret the positional tolerance if only half the position is included? What part of the locational dimensions becomes basic? There is no interpretation in ASME Y14.5M that would make this clear or that even implied this is allowed.

Matt Lorono
CAD Engineer/ECN Analyst
Silicon Valley, CA
Lorono's SolidWorks Resources
Co-moderator of Solidworks Yahoo! Group
and Mechnical.Engineering Yahoo! Group

 

[gurujeff33]

The zero of the ordinate becomes your datum so the basic is the distance between the zero and the ordinate you are attaching the position to.

Anyway instead of discussing if what he is doing is right there should be some sort of work around for properly place a GDT on an ordinate dim.

Do you need the leader for the GDT? If you select the ordinate then start the GDT function does it still interfere?

 

[fcsuper]

Guru,

Zero of the ordinate for this purpose can be true under a certain interpretion, but there is no support for this in the standard whatsoever, as far as I can tell. If the standard is invoked, the method stated above creates ambiguities, which is actually NOT allowed by the standard. Without further input from TLorich about this and given the nature of the question, my guess is there is a misapplied GeoTol.

To address TLorich's question directly, one doesn't need to have SolidWorks itself attach the GeoTol to the dim. If you need the GeoTol to be at a certain place (next to a dimension), simply create it on the drawing without attaching it, then move it manually into the appropriate position. Just make sure not to accidentally attach it to the dim, so the problem will again arise.

Matt Lorono
CAD Engineer/ECN Analyst
Silicon Valley, CA
Lorono's SolidWorks Resources
Co-moderator of Solidworks Yahoo! Group
and Mechnical.Engineering Yahoo! Group

 

[takedownca]

I agree with the several people that stated gtol would never be attached directly to an ordinate dimension. However, a similar case would be if you're calling out flatness, profile, etc on a surface located by an ordinate dimension. In this case, as Matt said, The gtol needs to be attached directly to the surface, not the dim. The gtol can however be located such that it lies on the extension line of the dimension.

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