On completing this lesson, you will be able to do the following
■ Describe dimensional constraints.
■ Create aligned and angular constraints.
■ Change a design by changing the values of the dimensional constraints.
■ Plot dimensional constraints for design reviews, and understand the
differences between dynamic and annotational constraints.
Command: DIMCONSTRAINT
Dynamic dimensional constraints control the lengths, radial sizes, and angles
of objects. They also control the distances between objects or points on objects.
For example, in addition to controlling the lengths of selected objects, you
might want to keep the distance between lines constant, such as the tread
length of stairs.
Let’s apply dynamic constraints to the drawing of the deck plan.
To create dynamic constraints
1 Open the drawing file, PD_Deck3.dwg.
This drawing is the deck plan with all the geometric constraints applied
Let’s verify that the geometric constraints are applied.
2 On the Geometric panel, click Show All to display all geometric
constraints.
3 On the Geometric panel, click Hide All.
4 On the Dimensional panel, click Aligned.
5 At the Command prompt, press Enter to specify the Object option.
6 Select the horizontal line as shown and then click a location for the
dynamic constraint.
7 Press Enter or click anywhere outside the box to accept the current length
of the line.
This step provides the opportunity for you to change the length of the
line.
8 Click Aligned again.
9 Create an aligned constraint for the bottom horizontal line as shown.
You will need the extra space later.
10 Create two more Aligned constraints on the vertical lines as shown.
You might wonder why we did not apply Horizontal and Vertical
constraints instead of the Aligned constraints. For this design, we want
to control the lengths of the lines. The Horizontal and Vertical constraints
control only the horizontal and vertical distances.
This distinction is important when you work with diagonal lines or later need to rotate a
drawing.
11 Zoom into the area of the stairs.
We will apply constraints on the tread length for each step.
12 On theDimensional panel, click Aligned.
13 Click the vertical line as shown, making sure that you see the endpoint
glyph.
14 Click the endpoint of the vertical line to the left, and click a location for
the constraint.
15 Press Enter or click anywhere outside the box to accept the value of 45.
16 Create an Aligned constraint between the next pair of lines as shown.
17 Repeat the process for the last pair of lines as shown.
Each of the endpoints of these lines will now maintain a distance of 45
cm from each other, and the parallel geometric constraints will keep the
lines parallel.
18 On the Dimensional panel, click Angular.
19 Click the two lines in the corner of the deck as shown.
20 Click a location for the constraint, and press Enter or click anywhere
outside the box to accept the value of 90 degrees.
Later, you will see why we chose to use an Angular constraint for this
corner.
21 Zoom out until you can see the entire deck plan as shown.
Now that we have fully constrained this deck design, let’s change some
of the parameters. There are several ways to do this.
To change dimensional constraints
As mentioned previously, before you modify a constrained design, it’s often
a good idea to apply one or more Fix constraints first. This keeps those objects
from shifting or rotating. You can always delete the Fix constraints later.
1 Turn on the display all Geometric constraints and verify that the two Fix
constraints are applied. Then turn off the display of all Geometric
constraints.
2 Double-click the d1 dynamic constraint as shown.
3 Click within the edit box and enter 1000 as the new value.
The entire deck was shortened slightly. Next, we will try to make the deck
plan a little less boring.
4 Double-click the ang1 dynamic constraint as shown.
5 Click in the edit box and enter 120 as the new value.
This design is more interesting, but still too timid. Let’s make the angle
larger.
6 Change the value of the ang1 dynamic constraint to 140.
This design is much more interesting. You might want to experiment
with other values.
7 Close the drawing without saving it.
To plot dimensional constraints
Dynamic constraints do not have the same purpose as the dimensions in a
construction document or a manufacturing drawing, nor do they maintain
typical dimensioning standards. Thus, dynamic constraints are not plotted
with the rest of the drawing. However, you might want to plot them for design
reviews. In those circumstances, you can change dynamic constraints into
annotational constraints.
Annotational constraints are plotted, have a static size, and use the current
dimension style.
1 Open the Properties palette.
2 Select a dynamic constraint.
3 In the Properties palette, under Constraint, select Annotational from the
Constraint Form drop-down list.
The resulting annotational constraint uses the current dimension style.
4 Close the Properties palette.
5 (Optional) Plot your drawing to a plotter or a printer.
Summary
You have learned how to apply dimensional constraints and how they work
with geometric constraints to control a design. You also learned how to change
designs by changing the values of dimensional constraints. Finally, you learned
how to change dynamic constraints into annotational constraints for plots
to be used in design reviews. Next, you will learn how to add formulas and
expressions to a design.
Review Questions
1 What is the most commonly used dynamic dimensional constraint that
controls the lengths of objects or the distances between them?
2 How can you change the value of a dimensional constraint?
3 What is the purpose of a Fix constraint?
4 What must you do to create a plot that displays dimensional constraints
for a design review?
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