Creating 3D Drawings - Mastering AutoCAD for Mac - page 512

3. Click a point roughly at the center of the box. The circle appears on the surface, and as
you move the cursor, the circle's radius follows.
4. Adjust the circle so it's roughly the same 6-unit radius as the one shown on the bottom
image in Figure 19.15, and then click to set the radius. You can also enter 6 ↵.
5. Choose Modify  Offset from the menu bar or type O ↵, and offset the circle 2 units
inward, as shown in the bottom image of Figure 19.15. You can use the Center osnap to
indicate a direction toward the center of the circle.
USING A FIXED UCS
If you're working in a crowded area of a drawing, or if you know you need to do a lot of work on one
particular surface of an object, you can create a UCS that remains in a fi xed orientation until you
change it instead of relying on the Dynamic UCS feature. Choose Tools  New UCS  Face from the
menu bar, and then click the surface that defi nes the plane on which you want to work. The UCS
aligns with the selected surface. Press ↵ to accept the face that the Face option has found, or you
can use one of the options [Next/Xflip/Yflip] to move to another surface or flip the UCS. Once
you've set the UCS, you won't have to worry about accidentally drawing in the wrong orientation.
To return to the WCS, click World UCS from near the bottom of the Tool Sets palette. You'll learn
more about the UCS in Chapter 20, “Using Advanced 3D Features.”
This demonstrates that you can use Dynamic UCS to align objects with the surface of an
object. Note that Dynamic UCS works only on fl at surfaces. For example, you can't use it to place
an object on the curved side of a cylinder.
Pushing and Pulling Shapes from a Solid
You've just added a 2D circle to the top surface of the 3D box. AutoCAD offers a command that
lets you use that 2D circle or any closed 2D shape to modify the shape of your 3D object. The
Presspull command lets you “press” or “pull” a 3D shape to or from the surface of a 3D object.
The following exercise shows how this works:
1. Make sure the Polar Tracking button in the status bar is turned on, and then enter
PRESSPULL ↵ at the Command prompt.
2. Move the cursor to the top surface of the box between both circles. (See the bottom image
of Figure 19.16.)
3. With the cursor between the two circles, click the mouse. As you move the mouse, the
circular area defi ned by the two circles moves.
4. Adjust the cursor location so the cursor is positioned below the center of the circle, as
shown in the top image of Figure 19.17. Enter 3 ↵ to create a 3-unit indentation, as shown
in the bottom image of Figure 19.17.
You've created a circular indentation in the box by pressing the circular area defi ned by the
two circles. You could have pulled the area upward to form a circular ridge on the box. Pressing
the circle into the solid is essentially the same as subtracting one solid from another. When you
press the shape into the solid, AutoCAD assumes you want to subtract the shape.