>> So in this lecture, we're going to talk
about sectional views or sectioning in terms
of the need for visualization.
This chapter can be typically one
of the most difficult for a student.
So be a little patient especially in the beginning
if you're having problems visualizing.
Sectional views are nothing but additional orthographic views,
okay, that we create in order to expose internal features
of the objects especially features
that will normally appear in a standard front upright views.
Here's an illustration.
Here's a 3D object.
And it's very easy to visualize if you have the isometric.
Here's the top view and here's the front view.
And what we notice in this normal multiview drawing is
that the front has a lot of hidden lines.
We know from experience that the more hidden lines an object has
in the view the more difficult it is to visualize that object.
So the hidden lines here in the front view indicate
that some parts are empty and some parts are solid.
And we need to help our audience determine which parts
of the drawing are solid, which parts are empty.
And the way we do that is by creating a sectional view.
And we do that by imagining a cutting plane.
Here's the cutting plane here and in this case,
we make that cutting plane slice right through the middle
of the object like this and then we remove the part of the object
that is in front of that cutting plane.
So we remove the front part and then we look at the object
in the same direction as the front.
The arrows here indicate the direction of the line of sight.
In the normal standard views,
we indicate the cutting plane's position right here.
This is the actual the cutting plane as show in the top view
and here's the directional of line of sight.
And the view below the top view is now the front view
after taking the cutting section and removing the front part.
Now we realize that all this section areas here are the solid
parts of the original object that were sliced
through by the cutting plane.
So the hidden lines here
in the original front view now become solid.
These are now visible because we've sliced
and removed the front part and as you can see,
we indicate this part here with section lines
that evenly spaced the 45 degree lines on this area
and this area indicating that those two L-shaped areas,
this L-shape area and inverted L-shape here are solid parts
of the object that were directly sliced
through by the cutting plane.
Other hidden lines like this two circles here becomes solid
because now you can see those two circles
after removing the front half of the object.
So as we noticed, sectional views have the
following elements.
Cutting planes, okay.
That's the plane you use to slice the object into two parts
and it's shown in one of the standard views as an edge view.
We have this 3D solid object that has --
looks like a shell and there are some other features inside
that we don't know and we're trying to clarify that.
As seen in the front view here, you have a lot of hidden lines.
So what we do is we take a cutting plane,
we also include a cutting plane arrow.
In this case, these 2 arrows here indicate the direction
of the line of sight.
After you slice the object,
we also have section lines right here.
An element of the actual full section.
These are the front view here
and this arrow view's here has been replaced
by a full section view.
And the section lines or hashing indicate areas
where solid material has been cut
through by the cutting plane.
Okay? Here's another illustration.
Here is the 3D object.
Before we cut it, we indicate the position
or it's in isometric.
So we indicate the position of the cutting plane
and the direction of the line of sight.
We remove in this case right part.
There is a couple of different ways of indicating the position
of the cutting plane and it's edge view.
Okay? The most common one is using this long short short long
series of lines.
Okay? Or this could also be dash.
I do not like this dash here
because sometimes student confuse it
with regular hidden line.
I prefer this line type.
With respect to the section lines or the hashing,
they should be evenly spaced between one sixteenth of an inch
to one eighth of an inch in the final drawing.
Generally they should be about 45 degrees but not parallel
or perpendicular to the outline of the object.
I will show you an example of this later
and why you should avoid that.
There are symbols that correspond
to a particular type of material.
And I will explain that later.
So with respect to the 45 degree, okay,
so generally okay do you the section lines along 45 degrees
unless the 45 degree direction end up being either parallel,
in this case here, to major object lines
or perpendicular to the object lines.
And the reason why we avoid cases a and b is
because your audience might confuse
between actual object lines and the section lines
that are either parallel or perpendicular.
So in cases like this, you just go a long direction
in that case, neither parallel nor perpendicular
to major object.
The symbols for the section lines also give you additional
information about the model.
The generic symbol is this equally spaced line.
So you use this is if you do not know what type
of material you have.
It's also used for cast iron or malleable iron.
Generally used for all types of materials.
Here's for steel.
Here's for bronze.
So different materials that are commonly used
in engineering have different hash symbols.
The good thing is you do not have to memorize this
because AutoCAD has a built-in library of materials.
As a general rule for sectional views,
we do not show hidden lines.
Here's the 3D object shown in its isometric
and here's the position of the cutting plane
and the direction of the line of sight.
Here's the original top view and the original front view
and we choose to position of cutting plane right here passing
through this hole in order to expose these features here
in the front view that are mostly here.
So here's the position of the cutting plane.
So we cut it here and here's the resulting front view.
And notice that this solid line here came
from this line here that is not exposed.
However that solid line is this solid line in the middle.
This hidden line in the middle.
These 2 hidden lines here, one to the left and one
to the right correspond to this back area here.
This one line, one edge going down here.
Another edge going down here which we did not expose
because our cutting plane did pass through those edges.
But notice that those two hidden lanes, the one on the left here
and one on the right here are not shown here.
Why? Because generally even those those lines still exist
corresponding to the edge here and this edge here,
we don't show them because it kind of defeats the purpose
of the cutting -- or the sectional view.
The main purpose of taking this sectional view right
at this position is to expose these features here
and leaving the hidden lines there would create confusion.
Visualization of sectional views can be challenging
because now you're not just trying
to visualize how the object looks from the outside,
you're also imagining having to slice through the middle
of the object and then trying to expose the internal features.
And like we did for multiviews and isometrics,
it is often very helpful to label planes
as well as vertices.
Some illustrations of sectional views.
Here's the regular top view and the regular front view
and regular right side view.
And we're going to try to attempt
to expose the internal features in the right side view
as indicated by this hidden line
by taking this cutting plane here.
So slicing it right through here and removing this part
and looking at it in this direction, of course,
that will result in our right side view
with its hidden lines being converted
into the sectional view.
The way it's illustrated here is you look at the parts
of the object that were solid right here that was sliced
by your cutting plane.
Don't forget to indicate the section lines
or the other solid parts over here.
And then do not forget that although you need not slice
through the cylindrical surface,
the cylindrical surface here curving this way was not
directly sliced by the cutting plane except for the quadrant
up here and the quadrant up there, down here.
However, you still see this line here corresponding the
cylindrical surface here and another line here corresponding
to this cylindrical surface and also the cylindrical surface
of this smaller hole here.
On the other hand, there's no line here
because this is not a cylindrical surface.
There is actually an empty space.
Different parts of sectional views.
The most common type is a full section.
It's called a full section
because the cutting planes cuts fully through the object
and removing exactly half of the object.
So here's an example.
The regular top view and regular front view, okay,
as you can see there's a lot of hidden lines in the front view.
So what we do is we're going to try
to clarify those internal features
by taking this cutting plane and taking this line of sight,
removing the front half as indicated here
and showing what's now visible.
So this the cutting plane
and here's the resulting full section
with this hidden lines being replaced by solid lines
and then this line is a curved line here
and this line correspond to this.
These two solid lines correspond to these two lines here
and as you can see the left and the right sides were solid parts
of the object that were cut through or sliced
through by your cutting plane.
Notice how the hidden lines become solid lines and now serve
as boundary of section lines or hashed.
Half section is one that does not cut
through fully through the object.
Instead only passes halfway through the object
and this is usually useful for symmetric objects.
An object here is the regular top view
and here's the regular front view.
We take a cutting plane over here.
Okay, but instead of the cutting plane cutting fully like this.
It only goes through half of the left half.
And take note that the cutting plane goes this way
and then stops there.
And here's the direction of the line of sight.
So basically we remove the left half of the front of the object.
So as we expose here, this hidden lines here become solid
and they become boundaries for the section line.
Notice, however, that if you compare the right part
of the regular front view and the right part of the front view
of the sectional view notice
that we now have removed the hidden lines.
That's generally, as we said
as a general rule we do not show hidden lines.
Another side of section is an offset section.
Here's an illustration of an offset section.
Okay? So instead of one whole plane cutting
through the object, the cutting plane line is not straight
but it's offset in order to pass
through important features of the object.
So this is what we do is we just offset the position
and here's the directional line of sight
and then we remove this part that is in front
of the offset cutting plane.
Notice that we don't show the cut form.
So right here where I actually did the bent right here.
So it's going through here
and then bent backwards a little bit, the actual position
of that is not important.
It could have been slightly to the right or slightly
to the left and as a result, we do not need
to show the cut formed by the offset because in reality,
if my cutting plane had to bend here,
there should be a solid line here
and notice we don't show that solid.
Okay? Because it's not important in what we're trying to do.
What we're trying to do is simply expose the features along
this position here of the cutting plane.
Aligned section is one in which it's cut at an angle
and it's usually used for the circular shapes.
It's cut at an angle.
So here's the position of the actual cutting plane.
So in this way and then bent along here, an angle.
Now if we rely on this actual direction of a cutting plane
and we look at it from the right, you will see
that the holes here will actually be foreshortened
because here the upper part of the cut through the hole
and here's the lower part.
Okay? We look at it directly from the right,
okay this arm here will actually be shorter
than it's actual length
because we're not viewing the length perpendicular
to the length itself.
So it kind of defeats the purpose of trying
to clarify the object to the sectional view so instead
of viewing it entirely from the right, what we do is
for the angled cut, we imagine that this arm is rotated
into this vertical position.
And that's why this is lowest part, okay,
which should have corresponded
to this vertical position is now all the way down here
because this whole arm is imagined to be rotated
into vertical position and that way we actually see the actual
size of this hole.
Another type of sectional view is the phantom section.
This is the exception to the rule
that there are no hidden lines in a sectional view.
So in a phantom section, then in a phantom section we --
although we still indicate the position of the cutting plane
and the direction of the line of sight, it's a phantom section
because we do not really cut -- take the cut.
We don't cut through here and remove the front part.
Instead we just imagine that we have x-ray vision like Superman
that can penetrate the solid objects to expose what's inside.
What you do is take the regular front view,
here's the regular front view okay and instead
of the regular section, you cut this line here.
This cutting plane here and then some
of this line will become solid, okay,
and then you add the section.
In this case, none of the hidden lines will be changed.
Why? Because we do not actually cut through the object.
It's a phantom section.
We pretend that it along this position of the plane
which ones are empty, which ones are solid.
And that's what we do by adding the sectional views.
There's a couple of reasons for doing this.
One is you notice here if we do the regular cutting section here
and remove the part, this detail here, this hidden line here
which corresponds to this hole is actually a hole
that is stored at the front part of the object not in the back.
So we remove this entire half here
in the front we will lose this detail here
or this hole in the front.
So instead of doing a regular section
like we just do a phantom section along this position here
which parts in the front view are empty.
So this parts empty.
From here to here solid.
And this one here is empty again.
Okay? And from here to here is solid again and this one here,
along this plane is empty again.
So what we did is we simply added the section lines
without changing any of the hidden lines to solid lines.
In other cases, phantom section is really --
you can think of it as an after thought.
You have the regular front view, or the regular views
and then you realize, oh I have a lot of hidden lines.
But I do not really want to change everything
into a regular section.
So I'm just going to help my audience by indicating
which areas along this cutting plane are solid and hidden
by adding the section lines
without changing any of the hidden lines.
So phantom section looks exactly like a regular view,
regular multiview except you add additional information
by indicating which parts of the object are solid
by adding section lines.
So the original hidden lines were kept.
Another type of section is a broken-out section
and here's an illustration.
So instead of taking a cutting section
through the whole thing that slices.
A cutting plane that slices this whole thing,
we just take a broken-out section here.
So we're simply interested
in exposing the details around this area.
So the break line, the jagged edge here corresponds
to, separates areas that were sectioned
from the un-sectioned parts.
Take note that there's no need to do the cutting plane.
All right because it's obviously really where the position
of the cutting plane is --
that you're trying to use to expose the details
in the broken-out section.
A revolved section, okay, is -- here's a nice illustration here.
Okay. So instead of creating a regular section, here's --
I can look at it from the top view and then in the front view.
So instead of creating a right side view, okay, to the right
like where my laser pointer is.
Okay. As a separate section --
sectional view to the right
of the front what we do is along this cutting plane we are going
to expose the details by taking the section
and then revolving it or rotating it by 90 degrees.
So that this "T" here okay is actually showing right
where the front view is.
Where it's rotated, 90 degrees.
So we revolve the cross section view 90 degrees about an axis
and the visible lines, right here,
right next to the revolved section can be drawn as out --
or as indicated drawing out could be broken-out.
The axis of revolution is drawn
on the revolved view as a center line.
Removed section, okay, it's very similar to the revolved section.
Okay. Except instead of revolving it in place
and putting it there, it's actually removed from the view
so you want it to be clear
and you create it right to the right of it.
And take note that we only show the details of the section
that you're trying to expose.
Okay? So the cross section is then draw adjacent
to the orthographic view.
So we, in this case, here's the slice
and we just show the removed section.
Remove it from the current position
and put it to the right of it.
And it's used when there's not enough room
for the regular orthographic view for a revolved section.
So if this gets too cluttered here, too clouded,
instead of doing a revolved section where you --
where this is, it's going to get confusing,
we just take the regular front view and just --
this part of the section we just remove and show it --