Take a look at the drawing
above. You'll see a complex assembly drawing and two different section
views. On the far left, you see the line that indicates where Section
B-B is. On the right side, you see the section view. Does it make sense
to you? What you are seeing is the cross section view of the metal beam
part of the of the bracket. It's shown so that you can see what size the
area is without having to look at the entire side view of the assembly.
Section views are used for clarity.
Look for the indicators for
Section A-A. Then look at the top right view. You'll see that the beam
part is shown as well as the hole that is drilled through it.
Section views are used in
Mechanical and Architechural drafting. Anytime you need to show some
detail that isn't readily seen from an exterior view, "cut it up" and
draw it.
Looking at Section Views
If you understand
Orthographic Projection and Hatching (you read the other two tutorials,
right?) then you should be able to handle section views easily. Have a
look at the image below and see if it all makes sense.
What you see is a very
simple block with a hole drilled. This shows that the section view and
the front view are almost the same. In fact, I just copied the Front
view down to begin the section view. I changed some linetypes and then
hatched it.
If you have more than one
part in your view, you will need to make sure that it stands out. Here I
have the same part as above, but with another piece placed inside it.
Here's an example of how a
section view can be used in Architechural drafting. By using standard
hatch patterns, someone else can look at the drawing and see that this
shows a concrete foundation with earth on one side.
I think by now you're getting the idea of how section views and hatching help to tell the story of what you are drawing.
Drawing Section views in AutoCAD
For this exercise, we'll
start with a simple drawing. Begin by drawing the part below, and as
you're drawing, think about what the section view will look like. You do
not need to draw the Isometric view, it is just for reference.
To draw the "Cutting Plane"
that marks the section, draw a line and then use the leader command to
make the arrows. Add text for the "A"s. Ok - what is your section view
going to look like?
The Cutting Plane points up
from the front view, It doesn't mean that it's pointing at the top
view, but in this case it works. Also note the the Cutting Plane is in
the middle. So if you chose the Top View, you're correct.
Copy the Top View. Straight
up will work fine. You can keep the dimensions. It's a good idea to
make sure that it is directly above the other view in case you have to
stretch part of it. Then you can do both views at once.
What lines need to be changed? Do you still need hidden lines?
This is what your Section view should look like before hatching:
Is it still making sense?
You needed to trim the line where the shaft on the right joins the part,
because in the section view, this is solid. You needed to change the
lines for the two holes from hidden to solid because they are not hidden
any more. You should now be ready to add a Hatch patten to the view.
The Hatch command might be a little different depending upon the version that you are using. This example shows AutoCAD 2012.
Start the Hatch
command and pick in the spots shown below. You want all three areas
picked at the same time so that the hatch creates one object instead of
three. This is needed so that you can edit the hatch and all the areas
will look the same.
The areas picked will fill up with the last used hatch pattern and settings that were used. That's fine, we'll edit them now.
This is a big toobar / ribbon for this command. There are really only three items you need to be aware of to make it work:
- Pattern: The pattern should indicate what material is used in the area that is hatched.
- Angle: Most of the time this will be 0 degrees, but sometimes you want to change it.
- Scale: This is the one that gets changed a lot. If your hatch pattern 'looks solid' - then you usually have to increase the scale because the lines are too close together. If the hatch pattern 'looks empty' - then you might have to scale it down because the lines are too far apart. The scale will vary depending upon what size your drawing is.
If everything went well, the Section view you have should look like this:
It's up to you if you want
to put your hatch on a separate layer. It can help a lot as you get into
more complex drawings. As you learn about printing through Layout Tabs,
think about how having your Hatch can be useful on it's own layer - and
maybe more than one layer.
Other uses for Section Views
Here is a section view that
is used to show a break in a solid bar and a pipe. This is a common way
of showing long pipes that don't fit in your drawing, just add a break,
but dimention the full length.
Here's an exercise for you: reproduce the image of a foundation below:
More exercises from Textbook of Machine Drawing. Draw these parts out in Orthographic View and then draw the Section view.
Conclusion
Section views are not
usually very difficult to draw, because you should have a lot of the
information first. You will draw your sections last and try to base them
off of existing drawings first.
If you have the
opportunity, look at drawing sets and see where they are used. If you
are drawing something try out a section view, it's good practice for
Hatching and also for developing your "CAD" eye.
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