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Dimension to Background Lines in a Section View
7

Dimension to Background Lines in a Section View

Dimension to Background Lines in a Section View

(OP)
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.

RE: Dimension to Background Lines in a Section View

Is the background line hidden?

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

RE: Dimension to Background Lines in a Section View

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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RE: Dimension to Background Lines in a Section View

(OP)
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.

RE: Dimension to Background Lines in a Section View

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.

RE: Dimension to Background Lines in a Section View

(OP)
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.

RE: Dimension to Background Lines in a Section View

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.

RE: Dimension to Background Lines in a Section View

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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RE: Dimension to Background Lines in a Section View

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.

RE: Dimension to Background Lines in a Section View

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." - Robert Hunter
 

RE: Dimension to Background Lines in a Section View

(OP)

Quote (Kenat):

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.

RE: Dimension to Background Lines in a Section View

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

RE: Dimension to Background Lines in a Section View

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." - Robert Hunter
 

RE: Dimension to Background Lines in a Section View

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.

RE: Dimension to Background Lines in a Section View

(OP)
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.

RE: Dimension to Background Lines in a Section View

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

RE: Dimension to Background Lines in a Section View

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.wink
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." - Robert Hunter
 

RE: Dimension to Background Lines in a Section View

(OP)

Quote (MintJulep):

I'd say dimension the depth in Section B-B.  
Section B-B was added in the last revision to do just that. I think it's much clearer that way. A composite section A-A (with a knee in it) would also work, I think.

From the sound of things, the initial detail wasn't illegal. Still, I think that it's much clearer this way.

RE: Dimension to Background Lines in a Section View

So I go back to my initial comment after you posted the first version.  The dimension itself is perfectly fine.

However, if within context of the whole drawing it could be confusing then that should over ride matters and may give cause to either crank the section line through the slot or add an extra view.  Like ewh kind of said.

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RE: Dimension to Background Lines in a Section View

I think disallowing lines not in the plane of the section cut is much too harsh.  Depending on the section it may be more or less clear.  My practice is by default to show what you call 'background lines' (and dimensioning to them is fine, too), and add a note the view if I do not show them.

RE: Dimension to Background Lines in a Section View

(OP)

Quote (SteveMartin):

My practice is by default to show what you call 'background lines' (and dimensioning to them is fine, too), and add a note the view if I do not show them.
I think that BACKGROUND FEATURES OMITTED FROM SECTION A-A or something along those lines would be a valid note. The reason for not leaving them in is they sometimes tend to clutter things up without giving added information. In my mind it's often a bit cleaner to omit them.

Really, though, it sounds like a matter of preference and style, rather than one of standards.

RE: Dimension to Background Lines in a Section View

For "background" lines visible in cross-sections Y14.3M-1994 gives something like this:
"3.6.1. Visible Lines. Visible lines behind the cutting plane are generally  shown. Selected lines may be omitted if greater clarity is gained."

I haven't found anything in any standard related to dimensioning of "background" features in cross-sections, but IMO this is acceptable and very often indispensible practice.

The only situation (that I can imagine at the moment) where I would not go for such dimensioning is for features that are visible in a background of cross-section but are not in the same projection plane as cutting plane.    

RE: Dimension to Background Lines in a Section View

I don't think it's a good idea to turn off the background lines in this case. I also think the dimension is fine as originally presented. The lines do not obscure anything and they are an accurate representation of what the part looks like from that view. Turning the lines off won't clarify anything.

I have seen cases where turning tangent lines either on or off makes a view more clear but I don't think I've ever seen a case where removing lines representing actual features did more good than it caused confusion. I always expect any view to accurately represent what the part will look like. I agree that excessive dimensions in one view can make a cluttered print but that's not the case here.

If you look at the parent view in the first print you provided, there is no dimension for the OD, ID, or counterbore. Will turning off the lines to those features in your parent view make the drawing more clear since those lines aren't "adding information"? To me, it would be a much more confusing print. I just don't think it's a good idea to turn off lines depicting features. I'm sure there are some cases where it makes perfect sense but this isn't one of them. I think that hiding feature lines should be more the exception instead of the rule.

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