Dimension to Background Lines in a Section View 7

[flash3780]

Quick question: Does it violate standards to dimension to a background line in a section view?

In my view, it's bad practice, but I'm not sure that it's explicitly disallowed by any standards. We do our drawings in accordance with ASME Y14.5-1994. Unfortunately, I don't have my copy with me at present.

Thanks for the help.

 

[ewh]

Is the background line hidden?

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

 

[KENAT]

What do you mean by a 'background line'? Off the top of my head it's not a term I'm familiar with.

I can't remember where it says about not dimensioning to hidden lines, if not in 14.5 I think it's in 14.3 but I don't see it now.

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[flash3780]

Not a hidden line, but a line that is in the background of a section cut. Perhaps a picture would help explain.

 

[KENAT]

While from the limited geometry you show I'm not quite sure what's going on, I don't see a fundamental problem with the dimension you highlighted.

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[flash3780]

Maybe it's just my preference. I generally don't allow dimensions in my check prints to features in a section view that the section doesn't cut through. Actually, I think it's clearer to turn off the background lines entirely.

 

[SDETERS]

I disagree. I dimension to these background lines when I do not want to add another view. What is the difference between dimensioning these background section lines and dimensioning different lines in say a normal front view. Does Depth of the features being dimensioned matter in a view? With the 3D cad software today one will get all kinds of lines, fillets line ECt. in drawing views. Is there a 3D software that will allow you to turn off these background lines? This Thread I will follow and see what others have to say will be a good read.

 

[flash3780]

Why not just cut the section through the feature that you want to dimension? In this case, a composite section cut through the slot (apologies, not shown) and through the large counterbore is simple enough to do.

I'm sure there are situations where it makes sense to do otherwise so long as it isn't disallowed, but I find it clearer to limit dimensions in section views to features in plane with the section cut.

 

[CorBlimeyLimey]

If the section line does not cut through the slots why/how are they being shown as solid lines in the section view?

If someone has changed their outlines from hidden to solid, that same someone should get their a$$ kicked.

 

[KENAT]

If the section doesn't cut through it how are they showing?

I still don't fully understand what you mean by background lines.

It sounds like maybe background lines are lines of geometry not actually visible, what would normally be 'hidden lines' if shown at all.

Dimensioning to hidden lines is not allowed per ASME drawing standards, I just can't remember the exact reference.

If this is the case then I lean towards what CBL says.

"Is there a 3D software that will allow you to turn off these background lines?" Depending what we mean by 'background lines' then yes, most software I've ever seen gives you control over what I'm used to seeing called 'hidden lines'.

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[dgallup]

It looks perfectly clear to me. I say go with it. They are not hidden lines.



"Is there a 3D software that will allow you to turn off these background lines?"

In Pro/E & I assume other CAD programs there is the ability to toggle a section view between "total" which shows the back lines and "area" which eliminates them. I normally do "total" unless the back lines are excessively busy or confusing in some way.

 

[ewh]

Showing the hidden lines in the parent view may make it clearer, but regardless, it is not incorrect to dimension to them since they are not hidden and are in a true projection.

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

 

[flash3780]

If the section doesn't cut through it how are they showing?

They're not hidden lines, simply lines from the background of the section cut (i.e. out of plane). UG & Pro/E let you turn them off... not sure about other software. In the case pictured, the section cuts through a center hole and features visable in the background (i.e. not in the plane of the section cut) show up.

My stance is, you take the section through specific features, and (in general) only those features should be dimensioned in that view. That way, it's more explicit what's being shown.

Perhaps it's not disallowed to dimension to background features, but that doesn't mean it's best practice.

 

[MintJulep]

I don't understand where these features are in the part.

 

[ewh]

It may not be best practice, but there are situations where multiple additional views would be required otherwise. It is also better practice than dimensioning to hidden lines.
I suggested that the hidden lines be turned on in the parent view as that would greatly help in clarifying just what those features are. If that was understood, I can think of no reason to require another section to add the dimensions in question. The goal is generally agreed to be creation of a clear, concise drawing.


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

 

[CorBlimeyLimey]

So the slots are cut into (or break into) the through hole?

If that is the case, the dimensions shown are OK. However, showing the slots as hidden detail in the main view would avoid confusion and very simply explain what is being shown.

 

[KENAT]

I'd take a look at ASME Y14.3 and see what it say. I'm still confused.

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[flash3780]

I see where the confusion comes from. I didn't post the whole drawing. It's just a component of a piece of test equipment, but I didn't want to put the whole thing in the internet.

Here's the other view showing the slots (been revised since last time).

The slots pictured show up in the background of the section cut (shown in my earlier post). Since they're out of plane of the section, I think it's less clear to dimension to them in section A-A.

From the responses above, it sounds as if it's not illegal, but I still feel that it's best practice to only dimension things that your section explicitly cuts through in your section view.

Actually, I think that it's the most clear to turn off the background lines entirely so the section is the only thing visable.

 

[MintJulep]

I'd say dimension the depth in Section B-B.

 

[ewh]

While they may be out of the section plane, their depth is still normal to the view and is acurately depicted, and can be dimensioned as shown. Now, if you were asking about dimensioning their width, that is another situation entirely.
Of course, if time and drawing space is available, you could add an individual section through the slots to show their depth, but I feel that it would be more of a luxury than a necessity.
If additional time and/or efort isn't available for another section, I still recommend showing the hidden lines in the section parent view. This would help in a clearer understanding of just what features are being referred to.

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