EXTRUDING TO CREATE 3D OBJECTS

The purpose of this lesson is to look further at the EXTRUDE command. As you saw in Lesson 3-7, it can be used to create a 3D solid from a 2D shape. Two other ways you can extrude (which you may have seen as options on the command line) are to taper the extrusion and the extrude a shape along a path. If you need to, you can also combine the two options and extrude along a path while tapering the shape (shown below).

One example where you can use extruded paths is to represent pipes in a drawing. You may not use the tapered path option, but at least it's there.

EXTRUDING ALONG A PATH

Draw a POLYLINE from 0,0 to 120,0 to 120,120 to 240,120 to 240,0 and then press <Enter> to finish the command.

Do a Zoom > Extents to see the polyline and then zoom out a little more. Your line should look like this:

Next you will put a 24 unit radius on all the corners. The easiest way to do this is using the Polyline option of the FILLET command.

Command: F <ENTER>
FILLET
Current settings: Mode = TRIM, Radius = 0.0000
Select first object or [Polyline/Radius/Trim/mUltiple]: R
Specify fillet radius <0.0000>: 24
Select first object or [Polyline/Radius/Trim/mUltiple]: P
Select 2D polyline: <SELECT THE POLYLINE>
3 lines were filleted

What you're going to do next is extrude a circle a long the polyline - or to be more accurate, the path of the polyline. This would be one way of drawing pipes in 3D. For this example, you'll draw a pipeline with a diameter of 12 units.

Next draw CIRCLE at the bottom right end of polyline. Use a diameter of 12 (radius of 6). Once you have that, you need to rotate it in 3D. This is covered in the next lesson as well. To do this, you will select the circle, select the axis you want it rotated around and then choose the angle.

Command: ROTATE3D
Current positive angle: ANGDIR=counterclockwise ANGBASE=0
Select objects: <SELECT THE CIRCLE> 1 found
Select objects: <ENTER>
Specify first point on axis or define axis by
[Object/Last/View/Xaxis/Yaxis/Zaxis/2points]: X Specify a point on the X axis
<0,0,0>: <SELECT THE BOTTOM RIGHT END OF THE POLYLINE - Make sure your Osnaps are on for endpoints>
Specify rotation angle or [Reference]: 90 <ENTER>

Your circle should have rotated 90 degrees and now you are looking at the side of it so the circle appears to be a line as shown in the image below.

Now comes the easy part. Next you will EXTRUDE the circle along the path of the polyline.

Command: EXT
EXTRUDE
Current wire frame density: ISOLINES=4
Select objects: <SELECT THE CIRCLE> 1 found
Select objects: <ENTER>
Specify height of extrusion or [Path]: P
Select extrusion path or [Taper angle]: <SELECT THE PLINE>

Note: After the Extrude command, the polyline will still be there. If you need to keep your drawing clean, remembe to erase the path if you don't need it any more. To see how it looks, view the object in the SW Isometric view, and use the HIDE command. It should look like this:

This is just one option available with the Extrude command. Try it on other paths and see how it works. You will find that if your circle is too large, it may not be able to be extruded on polylines with tight corners. Any object that can be extruded can be extruded along a path. A path can be any open object such as lines, arc, polylines, splines, etc.

For more practice, try to created a cord for your lamp (Lesson 3-8) using a Spline as the path. You can also extrude 2 circles along a path (make one one circle smaller) and then subtract the smaller diameter extrusion from the larger to create a hollow pipe.

EXTRUDING WITH A TAPER

Extruding along a taper gives you another option in your 3D toolbox. Here is an example of how it is done:

Draw a RECTANGLE 100 units by 100 units.

EXTRUDE the Rectangle 50 units high with a taper angle of 45 °. Here are the commands needed.

Command: REC
RECTANG
Specify first corner point or [Chamfer/Elevation/Fillet/Thickness/Width]: 0,0
Specify other corner point or [Dimensions]: 100,100

Command: EXT
EXTRUDE
Current wire frame density: ISOLINES=0
Select objects: <SELECT THE RECTANGLE> l
1 found
Select objects:
Specify height of extrusion or [Path]: 50
Specify angle of taper for extrusion <0>: 45

Here is what you should have:

Use the 3DORBIT command to view it at different angles (Click on the screen, hold the button down and move the cursor around the screen). Try extruding different shapes with various taper angles for more practices.

These options give you a lot of versitility within one command. You may not use these options very often in your everyday drafting, but they're good to know.