AutoCAD

LT On-line: Lesson 15

1 Jun, 2001 By: Mark Middlebrook


Stretch out with the Stretch command

Page 1: Not just your ordinary stretch

The previous two lessons covered object selection and editing techniques, with an emphasis on AutoCAD LT's command-first editing style. In this lesson, we extend those techniques to cover the Stretch command. Stretch is an immensely useful command-one that makes you wonder how drafters used to do it all with erasers and pencils-but it does take some practice to get the hang of.

Before you work through this lesson, make sure that you're familiar with "Object selection for all editing styles" and "Moving and copying: How far and in what direction?" in the previous two lessons.The procedures described here work with AutoCAD LT 98-2000i and AutoCADRelease 14-2000i.

Not just your ordinary stretch
The Stretch command's name is a bit misleading. In fact, it can stretch (make longer), compress, move, and even warp objects. The key to this flexibility is how you select the objects, usually with a crossing selection rectangle.

Note: You may hear a crossing selection rectangle referred to as a crossing window, crossing rectangle, crossing box, or crossing. All of these terms refer to selecting objects by specifying a selection rectangle in which the second corner that you pick is to the left of the first point. See "Object selection for all editing styles" for more information.

The Stretch command is superficially similar to Copy and Move. It has the same inscrutable base point and displacement prompts that I described in the previous lesson, and it shifts objects-or parts of objects-to other locations in the drawing. But, it also has important differences that often confound new LT and AutoCAD users to the point where they give up trying to learn or use Stretch. This is a mistake, because Stretch is one of the more valuable commands in the AutoCAD editing toolbox. Here's what you need to know in order to make Stretch your friend:

To use Stretch effectively, you must select objects using a crossing selection rectangle, as shown in figure 1. The other option is to use a crossing polygon, as described in the table in "Object selection for command-first editing". Save this more advanced option until you've mastered stretching with a crossing selection rectangle.

figure
Figure 1. Crossing selection rectangle.

Stretch operates on the defining points of objects-endpoints of a line, vertices of a polyline, and the center of a circle-according to the following rule: If a defining point is within the crossing window that you specify, AutoCAD LT moves the defining point and updates the object accordingly. For example, if your crossing window surrounds one endpoint of a line but not the other endpoint, Stretch moves the first endpoint. It redraws the line in the new position dictated by the first endpoint's new location. It's as though you have a rubber-band tacked to the wall with two pins, and you move one of the pins. You can see this effect in figure 1. The two vertical lines on the right of the figure move, because both endpoints of both lines are within the crossing selection rectangle. The four horizontal lines get longer, because only their right-most endpoints are within the crossing selection rectangle. The left-most endpoints of the horizontal lines don't move.

Stretch can make lines longer or shorter, depending on your crossing selection rectangle and displacement vector. In other words, the Stretch command really combines stretching and compressing. Figure 2 shows this effect: the upper horizontal lines get longer, the lower horizontal lines get shorter, and the vertical lines stay the same length (but move).

figure
Figure 2. Effect of the Stretch command.

You usually want to turn on Ortho before you stretch. Otherwise, you'll warp the objects. The effect, as shown in figure 3, is similar to what happens to a car frame when the car gets hit from the side. Fortunately, in AutoCAD, unlike in car accidents, you can just click the Undo button!

figure
Figure 3. Watch for warping.

Stretch out with the Stretch command
  Page 1: Not just your ordinary stretch
  Page 2: Stretch example


About the Author: Mark Middlebrook


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