Geometric Constraints in AutoCAD: Tuesday Tips With Frank

[The AutoCAD Blog]

Remember when you were first learning to use AutoCAD? You learned about the Line command, and probably created a rectangle shape out of four line segments. Not long after, you learned about the Rectangle command and subsequently the Polyline command. You found that your rectangle is actually a closed polyline. How handy!

But it doesn’t behave like a rectangle. Grip edit a corner and end up with a weird trapezoid shape. Maybe you’ve created a slot-shaped object using the Fillet command trick that I showed you in this post. Again, you don’t want it to lose its slot shape when you edit it. But, as the animation below demonstrates, that’s exactly what happens.

What’s a drafter to do? In this case, the answer lies in Constraints. Click on the Parametric tab of the Ribbon to get started. Yes, it’s a pretty busy menu with lots of icons. If you’re like a lot of 2D drafters, you’re probably aware of it, but have also probably never used constraints for anything.

Don’t worry, this isn’t going to be a full tutorial on how to use them. AutoCAD gives you a shortcut and does the work for you. On the left side of the Geometric tab, you’ll see a large Auto Constrain icon. Using it is extremely easy. You’ll be prompted to select objects… so select the objects you want to constrain. In our example, we’ll do the slot first and the rectangle second.

But first, there are a few things you’ll want to know if this is your first experience using geometric constraints in AutoCAD.

Working with Geometric Constraints in AutoCAD

Next to the Auto Constrain icon, you’ll see all of the types of constraints you can apply. These are things like perpendicular, concentric, or parallel. When a constraint is applied to an object, an icon of the constraint type will display at the affected geometric point. You’ll want to know that you can show or hide them using the tools to the right of the geometric constraint icons.

There’s also a very handy Delete Constraints tool in the Manage tab at the far right. You’ll be prompted to select objects. Choose what you want, or if you want to affect the entire drawing, just type in All.

Why did I want to make sure you’re aware of this? Imagine getting in a drawing from an external source, and nearly all of your attempts at editing it give you weird results. What could the problem be? Well, perhaps constraints have been applied, but all of their icons have been hidden. Just click on Show All, then Delete Constraints, and select all if you don’t want them. Badda bing – problem solved. **

OK, so we’re going to be using the Auto Constrain feature on the slot. It will apply whatever constraints that it finds to your selected object(s). In this case, it uses Tangent, Parallel, and Horizontal. Now, as we see in the animation below, grip editing the shape will now retain its shape.

That was easy. Two clicks and you’re done. But there may be some situations where Auto Constrain will constrain your object too much. You can also easily manage the constraints that it will use. For our Rectangle, we want to do just that, as if you use the default set, it will be constrained so much that you can’t grip edit it all.

Your only option while in the Auto Constrain command is to access the settings box. You can do this from the pull-down menu if you have Dynamic Input turned on, or by just typing S into the Command Line. The Constraints Settings dialog can also be accessed by clicking on the little arrow icon at the corner of the Geometric panel before using Auto Constrain. If you do it this way, you’ll need to make sure to click on the AutoConstrain tab.

By default, all constraint types but Equal are checked to be used. For our rectangle, we want to apply only the Perpendicular constraint. Again, this is very easy. Just click on the Clear All button, then click on the check for Perpendicular. Close the dialog with OK, and you’re ready to go.

Select the rectangle and then enter. The perpendicular constraint icons will appear, and now when you grip-edit the corner, it retains its shape.

That’s All Folks

Geometric constraints can be extremely powerful, or incredibly annoying (especially if you don’t know they’re there). In today’s example, I’ve shown you an easy way to use them to maintain geometric shapes.

As for my story about the incoming constrained drawing? I know this because it happened to me, and more than once. Well, actually, it would happen to my users. As the CAD Manager, I’d get the call or the message, and off I’d go to debug the problem.

And a final word of warning. Do not ever, under any circumstances, use Auto Constrain on all the objects in your neighbor’s open drawing and hide their icons while your co-worker is in the break room on April Fool’s Day. It is in no way funny.

We here at Tuesday Tips HQ do not condone this behavior and disavow any responsibility.

More Tuesday Tips

Check out our whole Tuesday Tips series for ideas on how to make AutoCAD work for you. 

The post Geometric Constraints in AutoCAD: Tuesday Tips With Frank appeared first on AutoCAD Blog.

View the full article