Dimension to features unseen

[tradosaurus]

I'm not sure how to phrase this question but can you dimension to parts not visible in an assembly?

I think this might be covered by Y14.5M 1.4 (g)

See attached drawing and dimensions marked with red circle.

Thanks

http://files.engineering.com/getfil...b10d96d71&file=Assembly_Dimension_Example.png

 

[KENAT]

Do you mean as in using "2X" when one of the instances isn't visible in the view?

I'd say it's OK so long as it's obvious what is meant. In a complex busy drawing it may not work, in a simple one probably fine.

If you mean is it OK to dimension to hidden detail, then no per your reference.

Posting guidelines faq731-376

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

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

 

[dgallup]

I don't see any dimensions to invisible objects in the drawing. It's a section view and in that view all the dimensioned objects are visible.

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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

 

[3DDave]

The 8 X 1 3/8 is a bit suspect as it isn't clear which face is the reference face for the gussets not oriented parallel, and even for the secondary location, are they to be located from the surface away from the overall plane of symmetry or from the same side (left) of the tube? It doesn't matter for performance, but could be a problem if the welder and inspector don't agree.

 

[tbuelna]

I did not see any dimensions attached to a hidden feature in your drawing. While there seemed to be a few dimensions missing, the rest looked OK and were not difficult to interpret.

Hidden lines are normally only added when they help clarify a view. It is not normal practice to dimension to a hidden line. If you need to dimension to a feature that is obscured in the view, you can break out the local surface obscuring the feature.

 

[tradosaurus]

I appreciate the responses.

Just for clarification I was not referring to hidden lines. I understand not to dimension to hidden lines. We use cut outs or other views when needing to refer to a hidden line.

The 8 x 1 3/8 dimension would refer to all 8 gussets from the point of view of each gusset. Because the gusset is located at the center of the each support I felt it would be self explanatory.

 

[Gilmiril]

tradosaurus,

The relevant clause in ASME Y14.5-2009 is 1.4 (g), which states:

(g) Dimensions should be arranged to provide required information for optimum readability. Dimensions should be shown in true profile views and refer to visible outlines.

That is a "should" statement that implies it's poor practice to dimension to hidden lines. In your drawing, the dimensions in question are shown in true profile views and actually do refer to visible outlines...you were second-guessing yourself because they also apply to additional features that you can see in the dimensioned view. There's nothing wrong with this so long as you provide enough views to make it very clear where these dimensions apply (your top and side views do that, and your isometric drawing makes it clear even for people that don't know how to read drawings).

This is clearly not the same as dimensioning to hidden lines, and I think other people brought that up as a way of prompting you to realize that you had conflated these two concepts (just my opinion).