Section of a section view & section view as base view - Bad practices?
Section of a section view & section view as base view - Bad practices?
(OP)
That taking a section of a section view and using a section view as a base view to project other views is bad drafting practice (except where unavoidable) I have been told often.
But are there any official standards out there which expressly say that such a view is wrong/not to be encouraged? Any specific reasons (logic wise or engineering wise) why these are bad practices?
But are there any official standards out there which expressly say that such a view is wrong/not to be encouraged? Any specific reasons (logic wise or engineering wise) why these are bad practices?





RE: Section of a section view & section view as base view - Bad practices?
Also, there are no logic or engineering reasons against it.
In fact, logic of engineering practices suggests just the opposite: Your "base view" is supposed to be the most informative representation of the part.
If section is the most informative view, then so be it.
I am including picture borrowed from the drawing manual that is using this "bad practice":
RE: Section of a section view & section view as base view - Bad practices?
Although, in SOME cases it MIGHT be the only way around, like adding changes to already established big and busy drawing.
Either way it still a matter of personal preference, the realm of "may" and "should"; certainly not "must" or "shall".
RE: Section of a section view & section view as base view - Bad practices?
I don't believe making a rule would be advantageous to this topic because the "exceptions" are so numerous and common that they start to not become so exceptional.
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NX8.0, Solidworks 2014, AutoCAD, Enovia V5
RE: Section of a section view & section view as base view - Bad practices?
The reason, as far as I can ascertain, that it is considered "bad practice" is that it provides the opportunity for mistakes and mis-interpretations and can cause ambiguity as to whether to show the geometry that is taken away in the section in the following section. It can also add confusion as to what exactly it is that you are looking at, especially if taken to extremes such as a section from a section from a section.
ôKnow the rules well, so you can break them effectively.ö
-Dalai Lama XIV
RE: Section of a section view & section view as base view - Bad practices?
Unless I'm missing something this effectively precludes section of a section.
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: Section of a section view & section view as base view - Bad practices?
SolidWorks will allow a section-of-a-section. Maybe not "legal", but it's possible.
RE: Section of a section view & section view as base view - Bad practices?
It is ¶8.2.5 in the 2012 edition.
ôKnow the rules well, so you can break them effectively.ö
-Dalai Lama XIV
RE: Section of a section view & section view as base view - Bad practices?
thread1103-191012: PROJECTION VIEW FROM A SECTION VIEW
touched on this previously
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: Section of a section view & section view as base view - Bad practices?
ôKnow the rules well, so you can break them effectively.ö
-Dalai Lama XIV
RE: Section of a section view & section view as base view - Bad practices?
The specific examples in which I have seen the use of a section of a section and section view as a base view are unfortunately examples of lazy draftsmanship. To top it all, the person who made them insists that such a rule is not mentioned/suggested in any standards.
The ASME quote on section of a section is pure gold for me in this context. Now if only I could find something similar on the unnecessary use of a section view as a base view.
RE: Section of a section view & section view as base view - Bad practices?
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: Section of a section view & section view as base view - Bad practices?
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
RE: Section of a section view & section view as base view - Bad practices?
"Know the rules well, so you can break them effectively."
-Dalai Lama XIV
RE: Section of a section view & section view as base view - Bad practices?
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: Section of a section view & section view as base view - Bad practices?
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
RE: Section of a section view & section view as base view - Bad practices?
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: Section of a section view & section view as base view - Bad practices?
That other thread you linked to talks about that... as a checker, I've had numerous discussions with drafters about this. Plenty of them make a section, then project to a full view. Bad practice, yes, but even if it weren't, seems to me, using the logic of orthographic projection, if one were to make a projected view from a section view, that view would appear "cut in half", not full. Have no idea why one would want to do that.
RE: Section of a section view & section view as base view - Bad practices?
I have tried to follow "local" practices when I first started this position, and sections from sections was one of them. I quickly realized how easy it is to get lost in a complicated model and end up drafting something far different than intended, just because it was so easy to get lost in the model relative to where the sections are "supposed" to be coming from. I now try to avoid such local practices whenever possible.
Fortunately, this company is doing it's best to follow ASME standards; unfortunately, it still takes exception to the section from a section rule.
"Know the rules well, so you can break them effectively."
-Dalai Lama XIV
RE: Section of a section view & section view as base view - Bad practices?
Where people get ideas like that? Then, if we project from the view that has "broken-out" section, do we show chunk of material ripped out of the part?
RE: Section of a section view & section view as base view - Bad practices?
RE: Section of a section view & section view as base view - Bad practices?
I guess we do:
RE: Section of a section view & section view as base view - Bad practices?
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: Section of a section view & section view as base view - Bad practices?
I guess it /could/ be exceptional, however in many contexts it is as common as lunch.
Imagining a cylindrical part with a lot of interior contouring, grooving, threading, and a keyway or broached-grooves parallel to the centerline of the part. I could see a section view being the best Base View, and then a section of that view showing the keyway or groove geometry.
Like I said - I guess "exception" is dependent on context. In the greater world-view of a standards organization, I guess it might be an exception, but it seems it would be a situation that arises often-enough to warrant consideration.
/2cents
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NX8.0, Solidworks 2014, AutoCAD, Enovia V5
RE: Section of a section view & section view as base view - Bad practices?
"Should" to me means "it's better not to do it the other way, but if you don't have a choice - do"
TWJR and KENAT, sorry, I missed the <sarcasm> tags when preparing my posts.
RE: Section of a section view & section view as base view - Bad practices?
Diego
RE: Section of a section view & section view as base view - Bad practices?
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NX8.0, Solidworks 2014, AutoCAD, Enovia V5
RE: Section of a section view & section view as base view - Bad practices?
Isn't the section view of a part basically a planar cross-section having an infinitely thin thickness? And if you take a planar cross-section of that infinitely thin part section, wouldn't the result simply be the intersection of two planes, or a line? What value would the section view of a line provide?
It's not specifically "bad drawing practice" to take a section view from a section view, instead it results in a drawing view that makes no sense.
RE: Section of a section view & section view as base view - Bad practices?
IME, MOST of the time, a section view is merely a view of the part, and what is beyond, with a certain portion sliced away. You still see the mass 'beyond'. It's usually not an infinitely thin slice. I've very, very, very rarely seen that type of section used, actually.
_________________________________________
NX8.0, Solidworks 2014, AutoCAD, Enovia V5
RE: Section of a section view & section view as base view - Bad practices?
RE: Section of a section view & section view as base view - Bad practices?
A section view (or sometimes called a section cut) always shows the component shape or construction at the cutting interface defined in the associated view. Sometimes offset sections are used where the cutting interface is defined by angled or offset lines. Sometimes developed sections are used where the cutting interface is a defined curve. But in every case the section cutting interface is defined by a 2D line/curve shown in a 2D view of the the part/assy. So by definition the cutting interface is a projection of the line/curve normal to the view it is defined in. And the result of the section cut are the boundaries of any solid areas that the cutting interface passes thru, or "slices". The only valid features defined in a section cut/view are those existing at the cutting interface. Sometimes features beyond the cutting interface are shown to provide some perspective or clarity to the view, but they are considered as reference and it is not usually acceptable to use them as a basis for defining features at the cutting interface.
The type of orthogonal projection view sometimes defined by a line passing thru the part/assy in a 2D projection view is called an auxiliary view, and they are given the title "VIEW X-X" rather than "SECTION X-X". These are different than section views/cuts since they are interpreted just like any other orthogonal projection view.
A few years back when I worked at BCAG, their drawing practice was that any section view should only show the profile of the solid parts cut by the section interface, with nothing shown in the background. And no cross-hatching was used. The CAD system (CATIA) even had a specific function called "section cut" for making these types of simplified drawing views.
RE: Section of a section view & section view as base view - Bad practices?
I'm in no mood, this morning, to go search through ASME docs to support my statement, and the detail and explanation you give seems like it's probably rooted in something more than "because I did it this way at one company before" so I'm not going to argue. But I will say that what you describe as an "auxiliary view" is quite commonly referred to as a Section View both in industry standards of my entire work history as well as the software defaults of every application I've ever trained on, from Dassault, Autodesk, Siemens, Rhinocerous, and others. It just seems very unusual for the commonplace industry standard as well as the software manufacturers (particular those who /do/ try to base their software on proper specs/standards) to deviate so commonly and universally from the rule you purport.
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NX8.0, Solidworks 2014, AutoCAD, Enovia V5
RE: Section of a section view & section view as base view - Bad practices?
And while orthographic views can be defined by a2D line/curve shown in a 2D view, axonometric views are also allowed. ¶9.2.3 Section Views states "Section views may be created
from orthographic and axonometric views. A resulting section view may be orthographic or axonometric."
Section views are not necessarily auxiliary views and visa-versa.
Y14.3-2012 ¶7.7 "Auxiliary views are used in orthographic projections to show true shape and relationship of features that are not parallel to any of the principal planes of projection."
If the cutting plane goes through the part at any point, the result is a section view. If the cutting plane is oriented so that it is not orthoganal and does not go through the part, it is an auxiliary view. Removed views can also be defined by a cutting plane which does or does not go through the part.
"Know the rules well, so you can break them effectively."
-Dalai Lama XIV
RE: Section of a section view & section view as base view - Bad practices?
plane and the observer is assumed to be removed", which leads me to think that the portion beyond the cutting plane is to remain, unless there is sufficient reason to remove it. This is not addressed directly in the standard, and sections without backgrounds (or partial background) are often used in industry and may be appropriate when drawing clarity is enhanced.
"Know the rules well, so you can break them effectively."
-Dalai Lama XIV
RE: Section of a section view & section view as base view - Bad practices?
In response to your comment I simply offer the attached screen captures showing the drawing view menu options provided by Dassault's CATIA V5 software application. As you can clearly see there are specific options for orthogonal projection views, auxiliary views, aligned and offset section views, and aligned and offset section cuts.
RE: Section of a section view & section view as base view - Bad practices?
I do have to mention that Catia V5 is a pretty old product and is originated with the French, who don't really have much respect for English translations.
One does have to give the French some credit in drafting. Without them and the snooty British (kickin' a lot of sand on this beach) there would not have been numbered pencils. The Brits had a gigantic lump of graphite and kept the soft, uniform stuff, exporting the contaminated material. A French company got tired of sand-contaminated graphite and ground it up, and mixed it with varying amounts of clay - more clay = Harder pencil. Eventually this resulted in the F, B, and H scales for pencil hardness which was much better than what the Brits made. For more info, Pretrovski's "The Pencil"
Overall, I would not gift any CAD company with being standards compliant, even in areas where there are standards. Some of them bend over backwards to every whim users have, regardless of standards; others aren't even bothered to keep up. I saw one of them dinged recently for failing to currently include the '2009 symbols in feature control frames.
RE: Section of a section view & section view as base view - Bad practices?
Don't be too hard on the French and CATIA V5. CATIA V5 is not an obsolete software, and in fact it is a de-facto standard CAD/CAE application currently used by most of the aerospace and automotive industry. As far as drafting standard compliance goes, CATIA V5 user settings can be configured to comply with any standard currently in use or any legacy standard you can think of.
RE: Section of a section view & section view as base view - Bad practices?
The problem I have with this statement is that if the cutting plane is "passing thru the part/assy", it is a section view and not an auxiliary view. The Catia snapshot agrees with this (notice how the auxiliary view icon is not sectioned, while the section views are). If the icons are taken literally then I agree that they infer a cutting line thru the part for auxuiliary views, but the arrows are facing the wrong direction; this is not per the ASME standard. I would not base my understanding of the standards on what any CAD software offers, but on the standards themselves.
You don't need an engineering degree to understand drafting standards.
"Know the rules well, so you can break them effectively."
-Dalai Lama XIV
RE: Section of a section view & section view as base view - Bad practices?
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems