Making “Smart” Drawings with Parametric Tools - Mastering AutoCAD for Mac - page 450

3. Click the center grip of the arc, and then right-click and select Rotate.
4. Move the cursor to rotate the arc. Notice that the “piston” that is connected to the arc with
a fixed-length line follows the motion of the arc just as a piston would follow the motion
of a crankshaft in a gas engine.
As you can see from this example, you can model a mechanical behavior using constraints.
The piston in this drawing is a simple rectangle that has been constrained in both its height and
width. A horizontal constraint has also been applied so it is capable of moving in only a hori-
zontal direction. The line connecting the piston to the arc is constrained in its length. The coin-
cident constraint connects it to the piston at one end and the arc at the other end. The arc itself,
representing the crankshaft, uses a diameter constraint, and a fix constraint is used at its center
to keep its center fixed in one location. The net result is that when you rotate the arc, each part
moves in unison.
The Bottom Line
Use parametric drawing tools. Parametric drawing tools enable you to create an assembly
of objects that are linked to each other based on geometric or dimensional properties. With
the parametric drawing tools, you can create a drawing that automatically adjusts the size of
all its components when you change a single dimension.
Master It Name two examples given in the beginning of the chapter of a mechanical
assembly that can be shown using parametric drawing tools.
Connect objects with geometric constraints. You can link objects together so that they
maintain a particular orientation to each other.
Master It Name at least six of the geometric constraints available in AutoCAD.
Control sizes with dimensional constraints. Dimensional constraints, in conjunction with
geometric constraints, let you apply dimensions to an assembly of objects to control the size
of the assembly.
Master It Name at least four dimensional constraints.
Put constraints to use. Constraints can be used in a variety of ways to simulate the behav-
ior of real objects.
Master It Name at least three geometric or dimensional constraints used in the piston
.dwg file to help simulate the motion of a piston and crankshaft.