Join John Helfen for an in-depth discussion in this video Understanding constraints, part of Autodesk Inventor 2018 Essential Training.
- [Voiceover] Before we begin to learn about sketch geometry, we need to take a minute to learn about sketch constraints. There's two different types of constraints in Inventor when it comes to sketching. There's dimensional constraint and geometric constraints. We're gonna look at the geometric constraints right now. I've gone ahead and created a Sketch Practice.ipt file that has a single sketch with some predefined geometry. This will allow us to explore sketch constraints more closely. Let's go ahead and activate the sketch by double-clicking on it in the browser.
You can now see that the Sketch tab is active and we're ready to look at sketch constraints. A constraint by definition limits or restricts something and in this case, it's gonna restrict the motion that can be made by a piece of geometry. Let me show you what I mean. If you right-click in the Graphics window, you have an option to Show All Degrees of Freedom, and if you right-click a second time, you have the ability to Show All Constraints or F8 on your keyboard. By turning both of those on, we've had new information placed in the Graphics window.
When we turned on the degrees of freedom, all the red arrows became active, and when we turned on the sketch constraints, all of the locks became active. The locks are just a type of constraint. They're a fixed constraint. These are constraints I applied to this sketch geometry in order to make it so that you actually go through this course. The red arrows tell us a little bit more about how geometry can move. Let's go ahead and zoom in on the horizontal constraint up here in the corner. You can see on this line that each endpoint has arrows in all direction.
The center point has an arrow that kinda rotates. To see that motion, you can left-click + drag on an endpoint, and you can see that the line does rotate and the endpoints can move in any direction. That's what we expect. Let's go ahead an apply a horizontal constraint to this line and see how that constraint affects the geometry. The sketch constraints can be found on the Sketch tab under the Constraint panel here in the menu. The Horizontal Constraint is near the center. By clicking on that, we're now active in the horizontal constraint and we can apply that to a piece of geometry.
Now, when we hover over the geometry, you'll see a heads-up display with a horizontal line just helping remind and show you what type of effect this is gonna have on the geometry. If we go ahead and left-click on that geometry, you'll notice a few things happened. First, the circular, or rotational, arrow was removed, and then the up and down, or vertical, arrows on the endpoints were removed. I'm gonna right-click and select OK to get out of the command, and we can look at that a little more closely. If we left-click + drag on the endpoint now, it can move and make the line shorter or longer, but it can't move up and down because we have applied that constraint.
We've added the intelligence to this piece of geometry to tell it it should always remain horizontal and that's what it's doing. The other thing that happened was the constraint was applied. Now, they do get stacked up on each other a little bit and you can left-click + drag each of the constraints to make things a little more clear, and if you hover over the lock icon, you'll see that the center point highlights. That indicates that this lock is affecting that center point, and then if you hover over the horizontal constraint, the entire line highlights. That indicates that this horizontal constraint is affecting the entire line.
Now that we've seen that, let's go ahead and clean up the user interface just a little bit. We'll right-click and we'll select Hide All Constraints, which is F9 on your keyboard, so remember, you can toggle them on and off with F8 and F9 on your keyboard. Now, you can also turn off the degrees of freedom if you wish. I'm gonna go ahead and do that, but if you still feel that they provide you good information, you can leave them on for now. Next, let's go ahead and apply a Vertical Constraint. Just like the horizontal constraint, it works the exact same way, except it's gonna make the line vertical instead of horizontal. By clicking on it, you can see that it rotates around that center point to become vertical.
We'll right-click and select OK to get out of that command, and now we're ready to apply a colinear constraint. A colinear constraint will make this line and this line perfectly in line with each other. Because this line is fixed, if you left-click on it, you can see the constraints that are applied to a piece of geometry. In this case, it's just fixed in space, so let's go back to the Constraint panel and select the Colinear Constraint. If you hover of a button for a moment, the heads-up display will bring up the help, describing how this specific constraint works.
I'm gonna go ahead and click that and then select the first piece of geometry, and then the second line, and you'll see that they are now in line with each other and they both have a colinear constraint applied. Remember that at any point after you're out of a command, you can click on a piece of geometry to see what constraints are applied to it, and if you hover over that, you can see the pieces of geometry that are actually included or affected by this. Next, let's zoom out and move down to the concentric constraint. Here, we're gonna make the center points line up exactly.
The Concentric Constraint is here at the top of the menu and all you have to do is select the first circle and then select the second circle and the center points are now aligned with one another. If we slide to the left a little bit, we can go to the tangent constraint. The tangent constraint will make this line become tangent to the circle. Right now, if we left-click + drag this, you can see that this line is not tangent. It intersects this circle at two different points. A tangent line only touches the circle at one point, so let's go ahead an apply the Tangent Constraint.
We select the line and then we'll select the circle, and you can now see that a tangent constraint is applied and the line only touches the circle at one point. If we left-click + drag on the endpoint of the line, you can see that the circle adjusts so that it is always touching that line at one point. Finally, we can look at the perpendicular constraint. The Perpendicular Constraint, essentially, lines up two pieces of geometry so that they're at right angles to one another. If we left-click on the green line and then left-click on the horizontal line, you can now see that they're perpendicular to each other or they're at 90 degree angles from one another.
Hopefully, this explains how sketch constraints affect geometry, and shows how much power they can actually provide when you're sketching.
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