Part 3
Module 14: Trimming and Extending
Learning Outcomes
When you have completed this module, you will be able to:
- Describe the geometry of regular polygons.
- Apply the TRIM and EXTEND commands to shorten and lengthen drawing objects at selected cutting edges.
Geometry Lesson: Regular Polygons
A polygon is defined as any plane figure bounded by straight lines. A regular polygon is a polygon that has equal angles, equal sides, and can be inscribed or circumscribed around a circle. AutoCAD has a command to automatically construct polygons and it will be taught in a future module. For now, it is important for you to be able to construct polygons using geometry.
The first nine regular polygons are shown in Figure 14-1.
Any regular polygon can be inscribed in or circumscribed around a circle as shown, using a hexagon, in Figure 14-2.
It is important to understand and know the geometry involved to construct a triangle, square, hexagon, and octagon as shown in Figure 14-3. Study each one and try to understand how they are constructed and the angles used to construct them.
The following are the steps used to draw a hexagon in an AutoCAD drawing. See Figure 14-4.
Step 1
Draw 6 lines on layer Construction from the center to each corner, 60 degrees apart.
Step 2
Draw six lines snapping from the end of one line to the end of the next line.
Step 3
Turn layer Construction off.
Trimming and Extending
Not every object can be drawn using exact coordinates or locations as has been taught to this point in the book. There are times where it is essential that objects be drawn to approximate lengths and sizes and then trimmed or extended to their exact size and location. This does not mean that you can guess at the size and location of the objects. Objects must still be drawn with 100 percent accuracy. The length can be approximated and then adjusted using the TRIM or EXTEND commands.
In AutoCAD 2021 there have been changes to the Trim and extend commands and the default settings will not produce the expected results in the following tutorials. The default MODE setting, QUICK, will give access to the [cutting edges/Crossing/mode/Project/erase] options, which should be set as explained later in this tutorial. Then, as a last step, the mode should be set to standard. This will produce the expected behavior of TRIM and EXTEND. If you do not see the above options, set the MODE to Quick, make the setting changes and then restore the MODE setting to Standard.
AutoCAD Command: TRIM
The TRIM command is used to shorten objects to meet the edges of other objects. It is not required for the object being trimmed to intersect with the object forming the cutting edge.
Shortcut: TR
AutoCAD Command: EXTEND
The EXTEND command is used to lengthen objects to meet the edges of other objects. It is not required for the object being extended to intersect with the object forming the cutting edge.
Shortcut: EX
WORKALONG: Using the TRIM and EXTEND Commands
Step 1
Start a new drawing usi