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If you are someone who creates drawings using geometric constraints, you know that it's a two-step process. First, you have to create your line work, then you have to come back and apply your constraints. Well, AutoCAD 2011 cuts our work in half, by allowing us to apply our constraints automatically as we draw. In this lesson, we are going to learn how to use inferred constraints. On my screen I have a simple mechanical part and this part has several constraints applied to it. Now, they are not showing up on screen right now. To turn on my constraint bars, I am going to go to the Parametric tab and in the Geometric panel, I am going to select Show All.
If we hover over the constraint bar, we can see the relationships between the entities. Now, I would like to recreate this geometry, but I don't want to do it the typical way. I don't want to create the line work and then add the constraints afterward. Instead, I am going to use the new Infer Constraints toggle in the status bar. By turning this guy on, AutoCAD will keep an eye on the line work that I am creating and it will add my geometric constraints automatically. Since the tool is turned on, I am going to go back to the Home tab. I will launch my Line command and I am going to create a line from right here.
My Ortho happens to be locked. I am going to pull this straight down and enter a distance of 10. Now, this is a little bit longer than what I need, but since this part's going to be parametric, I can always change the dimensions later. Now that I am finished, I will hit Escape. Notice that AutoCAD recognized that this was a vertical line and it applied the appropriate constraint. Let's offset this line next. I will launch the Offset command, I will enter a distance of 6, and I will offset this line to this side, and I will hit Escape.
To create the rounded top, I am going to use the Fillet command. Now, I know what you are thinking, these lines are parallel, they doesn't intersect. It doesn't matter. We can fillet parallel lines in AutoCAD. Simply launch the command, click one line and then the other. Since our Inferred Constraints toggle is turned on, our arc is not only coincident at both ends. It's also tangent at both ends. I would like to create another line segment. We will launch the Line command, and I will create a line from this endpoint to Shift+Right Click, perpendicular to this line.
And I will hit Escape. Once again, AutoCAD automatically applied the appropriate constraints. Let's add a circle. I will launch my Circle command and I will create my circle from the center of this arc. We will give it a Radius of 1.5 and I will hit Enter. Finally, I will create the rounded corners. Once again, I will use the Fillet command. Let's launch Fillet. I will right click and select Radius. It looks like we need a Radius of 1 and the default happens to be 2. I am going to hit Enter to accept the default, even though that's incorrect.
It will just give us another opportunity to edit our geometry in a little bit. Let me select my first line, and before I select the second one, take a look at this coincident constraint. When I grab the other line, that constraint was no longer needed, so AutoCAD got rid of it. We can see that right here. So not only will AutoCAD add constraints when necessary, it will also remove them if it's necessary. I am going to hit my Spacebar to go right back into the Fillet command and I will select this line and this one. Now that my geometry is essentially finished, I would like to make one more change.
I am going to go to the Parametric tab and I would like to create an equal constraint. So we will select the Equal button and I would like this arc to always be equal to this one. Inferred constraints aren't going to take care of everything. Occasionally you will have to add some constraints manually. All right. Now that I have completed my part and my constraints. Let's make this geometry match the part on the right. I will start by selecting this arc and I will grab the triangular grip. This gives me access to the Radius. I will set this to 1 and hit Enter.
Then I will hit Escape to deselect the line work. I am going to select this line, grab it by the midpoint grip, and I will pull this down, such that these are approximately the same level. Once again, I will hit Escape when I am finished. Then we will select this arc. I will grab the triangular grip and we will set this guy to a Radius of 3.5 and hit Enter. Finally, I will select this line. We will select this grip. I will hit my tab key to put the focus on the total length of the line and I will set this to 8 and hit Enter, and that essentially completes my part.
Now, since we have been grip editing our parametric geometry, let me show you another quick change that occurred in AutoCAD 2011. If I select this arc and then select this grip, when I move my cursor I am obviously changing the geometry of my part. If I wanted to edit the arc only, I would press and then release my Ctrl key, and AutoCAD relaxes those constraints and lets me change this geometry. I am going to drag my arc out to here and click. Now, since I did violate some constraints, AutoCAD removed those constraints for me automatically.
Let's click on Do to put this back. Since I am finished with my part, I am going to come down and turn off the Infer Constraints tool. This is probably good practice, because the setting of this tool stays constant between your AutoCAD sessions, and this way I am not adding unnecessary constraints in this drawing or another one. Using Inferred Constraints can be a great time saver when drawing. By turning on this toggle, AutoCAD will keep an eye on your work and add or remove geometric constraints automatically.
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