In this lesson, you'll begin using true 3-D commands. First
you will create a 2-D region and then extrude it into
a 3-D solid. Then you will add 3-D surfaces to the tops
of your previous drawing (line thickness) to
close the
back, sides and seat.
Begin a new drawing with the acad.dwt template.
Create 3 layers called SIDES, SEAT, and BACK and
give them different colors.
Draw the outlines (using rectangles) of the back, sides
and seat as you did in Lesson 3-5, but
don't add line thickness.
You'll start by creating a region for the back of the chair.
Make sure that back is your current layer. (Any region
you create will be on the current layer, regardless of
which layer the object was on when you selected it.)
Start the region command by entering REGION (or REG)
at the command line. Pick the polyline that will become
the back of the chair and press enter. Your command line
should look like this:
Command: REGION
Select objects: <SELECT RECTANGLE> 1 found
Select objects:
1 loop extracted.
If the Region wasn't created, it usually means that you
have a gap in the shape. Polylines must be closed to
be used for Regions. Repeat this for the other polylines representing the 2 arms and the seat,
ensuring that you have the correct layer current.
At this point, you have four 2-D regions. The next step
is to extrude them into 3-D solid objects. Make
BACK the current layer and start the EXTRUDE command.
Pick the region on the back layer. Look at the command
line. You will be asked a few things:
Command: EXT EXTRUDE
Current wire frame density: ISOLINES=4
Select objects: <SELECT REGION> 1 found
Select objects: <ENTER>
Specify height of extrusion or [Path]: 34
Specify angle of taper for extrusion <0>:
The
first thing that AutoCAD needs is the height of the extrusion.
This is similar to the thickness that you gave the polylines
in lesson 5. Remember that if you give a positive number,
it will extrude in the positive Z-axis. If you give a
negative number, it will extrude the region in the negative
Z-axis. Then you are asked for the 'Extrusion Taper Angle'.
In most cases this will be the default of zero. Press <ENTER> to accept the default.
Note: You can also extrude directly
from rectangles, circles and closed polylines, but I
wanted to show you the Region command.
Extrude the
sides and seat. Remember to move the seat up 12" if you
haven't already. Check that the model is correct by viewing
it in the SW isometric view. Type HIDE (HI) and
you should see a solid chair like the one below.
Now you can see how solids are a good
way to go in some cases. They will usually give you the
most accurate way of viewing the model. You can also get
a lot of information out of a solid. Start the Mass Properties commands (MASSPROP). Click on one of the solid objects and press <ENTER>. You'll
see that AutoCAD can give you a lot of information about
it. A lot of these are useful in engineering applications,
but the volume is something that may be needed in many
different instances. As you'll see in the next lessons,
you can do a lot with solids.
Save your drawing under the name: chair_extruded.dwg
NEW PROJECT
Open your chair_line_thickness.dwg drawing and immediately
save it under a new name: chair_3D_face.dwg
What you're going to do is add 3-D faces
to the tops of the back, sides and sides. Begin by viewing
your model in the SW Isometric view. Type hide to
see where you need to cap off the extruded lines. Type REGEN or RE to
regenerate your screen so you can see all the corners
again.
Make sure that BACK is the current layer. Type 3DFACE to
begin the command. You will be asked to select some points.
Make sure that your endpoint Osnaps are on.
When asked to pick the points, select them in the order as
if you were drawing a rectangle. Do not go from one corner
to an opposite one. After you have picked the fourth
corner, press (enter). Your command line should look
like this:
Command: 3DFACE
Specify first
point or [Invisible]: <1>
Specify second point or [Invisible]: <2>
Specify third point or [Invisible] <exit>: <3>
Specify fourth point or [Invisible] <create three-sided
face>: <4>
Specify third point or [Invisible] <exit>: <ENTER>
Repeat the command to add 3-D faces to the top of the sides
and the seat. 3D faces are great for making odd shapes
that include any four lines (or arcs) that are touching).
Enter the HIDE commands
to check that it was done correctly. If it all worked,
you should see an image that looks identical to the solid model.
You'll notice that the 3D face covers what would be the
opening at the top of the arms and the back. If it was
done incorrectly, there may be a line running down from
the back corner of each piece.
Save the
file.
Now you have created some true 3-D objects. Take some time
to think about how much work was involved in each method: Wireframe, line thickness and extruding.
Think about instances where one might be better than
the other. Review the methods that you have used so far.
Extra Practice: Create a 3D solid model of this drawing. Start with the bottom profile and create a region, then extrude the region. Save this and other exercises for using in Lesson 3-9 (adding materials).
Extra Practice: Create a 3D solid model of this drawing.
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