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A very common place to find curves in a building is in arches. Arches can be employed over doors, windows, or openings. Since these items when created in Rabbit are actually component families, it's often desirable to make your arches parametric. This way, when the width or the height of the door or window is adjusted, the arch can adjust accordingly. Now of course, arches come in many shapes and sizes, but in this and the next few movies, I'm going to focus on just a couple of the shapes. And specifically in this movie, I'm going to look at the segmental arch.
Now to get us started, I'm in a file called FB Seed, FB stands for face based, and of course, it's a seed family. Now this seed family is very similar to the seed family that we created together in an earlier chapter. You can find it in the seeds family folder in the exercise files. If you have access to the exercise files. And it's a very simple family that is face based. So what exactly does that mean? Well I talked about face based a little bit in the hosting a nested family on a reference line movie in the, Revit family editor course here at lynda.com.
But let me give you a brief explanation of how a face space family works. It does require a host. But the host is actually a surface. It's a face of some other 3D geometry. So this rectangle that you're seeing out here is actually sort of a stand in surface. And you can see that best if you open up the 3D view and kind of take a look. So this surface here, represents the host or the face that you'll have when you load this into a project. So, you're going to build your geometry on the surface of this face.
This extrusion does not go into the file when you load it in. It gets left behind, so it's just here for reference. So I'm going to close that out. Otherwise we're going to work with this family in pretty much the same way as we've worked with other families. So I set up the reference planes and the dimensions in pretty much the same way as our other. Seed family. So I got a right and a left reference plane. A front and a back reference frame. A d and a w dimension. And I also included an h dimension for the height in this file as well.
So everything flexes and works like everything we've already seen in previous movies. And when were finished working with this family and we load it in, we'll see the face based part of it in action. So the first step that I want to do is reconfigure the dimensions a little bit to describe the shape of the arch that we want to build. So the height that were going to be describing is actually going to be the distance from the spring line of the arch up to the top of the arch. And so I'm going to use the center back reference plane that was already part of this file as the spring line for this arch.
In fact, if you wanted to, you could even select this and rename it. There's nothing special about the center front back name. It's not a required name. So if I want to read this to spring line to make it clearer, that's what I intend to use that for. Its just as easy as selecting it and typing in a new name right there on the Properties palette. Next I'm not really going to want this reference plane at all. So I'm going to delete that. Now of course when I do that it removes the d dimension and half of the equal equal.
Now the dimension is left behind I'm going to use that as my height essentially of my arch. So I'm going to use the h dimension that I've previously defined because I'm thinking of that as the height of my arch. And then later I will use the d dimension is actually the depth of the arch itself. So that So that's going to be the distance moving from the surface of the plane towards me. Okay and that'll be the depth of the arch. So you can see here I've defined the height now to this line, and I've kept my width right there.
So the next thing that I want to do is place my arc. Now I'm going to build my arch as a sweep, so I'm going to go to the create tab, click the Sweep button, and then I'm going to sketch the path. So for this one, I'm going to use the center end radius arc. So I'm going to click that tool. My start point for the arc is going to be the intersection of the left and of the spring line. The end point of the arc is the intersection of the right and the spring line.
And when I start moving to place the third point, the third point is actually indicating the radius of this arch. Now in the illustration that I showed you on screen when I started we movie, there was a few different arches in there. If I leave the proportions set the way they are, width and height And I snap right here. What I've basically created is a Roman Arch. Because you'll see that I have a half circle. Let me press escape here to cancel out of the sketch mode for drawing the path.
If you flex the height, what we want to happen to is we want the arch to kind of flatten out a little bit, therefore becoming more of a segmental shape, more of that eyebrow shape. So what we can't do for this particular family; is we can't lock the center point of the arch If we lock the center point, like we've done in previous movies, then we would be forcing this to always be a Roman arch. So if you want to kind of make a permanent Roman arch.
A full half circle. Then you can lock down the center point. But what we need to do is lock it differently. Constrain it differently than we've done previously. So that we have the flexibility of being able to flatten out that arch if we want to. So, you'll notice that we got several automatic sketch dimensions, of course. So, the next step that I want to do is, to begin locking things down. So I'm going to go to my align command, just like we've done in previous movies. Pick my left reference plane, get my end point of my arch, lock it.
My spring line. End point of the arc, lock it. Repeat that on both sides. So it's four alignments and locks. So, that locks the two end points, but now I want to be able to make the height of this arch parametric. I want to be able to vary that. So here's the trick that we need to do a little bit differently. We can't do this with reference planes. We can't do this with the alignment command. So the trick here is to add a dimension. So we're going to choose an aligned dimension.
DI is t shortcut. I'm going to start dimensioning from the spring line. And then I'm going to come up here and highlight the actual sketch line. Now, normally you wouldn't do this. Okay? We typically try and avoid doing this, but in this case it's going to become necessary. Just like it was necessary when we built a parametric ellipse a couple movies back. So here we're going to click right on the sketch line and then just pull the dimension out here somewhere. Cancel out of that. Select that dimension, and I'm going to label it with the same h parameter that's being used to drive this reference plane.
In fact, we don't really need this reference plane at all. We just have it there because people typically like to see the reference plane and it kind of defines the height. But technically, this is doing all the heavy lifting. I'm going to deselect the dimension and then, I'm going to go ahead and finish the Edit mode to finish the path. So, there's my sweep path. And then I'll open up my 3D view, orbit slightly so that I can get a better look, and we need to just draw something right here to represent the shape of the form that we wannna push along this arch.
So, I'm going to do Edit Profile and draw a simple rectangle that starts here and is about this big. For now, I'm just going to eyeball this, we can come back and make that parametric later. Finish it. Finish again. And you can see my arch form right here. Now let me go ahead and tile this two windows, w + t. So that we can see it in 3D and in 2D as we flex. So now because the dimension is directly on the sketch, if I take my H dimension and I flex that, let's try 0.5, you're going to see that arch begin to flatten out.
If I take the width and widen that out. Take the width again make it narrower. You can try as many different sizes as you want. But notice that in each case, the arc is still constrained with three things. Right? So in a previous chapter we talked about how you needed to lock down three things of your arc. In order to make it parametric. Here we've got the end point. The end point, but we're also dimensioning the arc itself. So essentially what's happening is the center point is being allowed to move.
So by dimensioning from here to here, we're essentially setting up a cord length, and allowing that center line to move. And it still controls the arch in the same way. So, of course, you could go in and make the shape of the arch anything you like. You could make it, you know, parametrize this rectangle to make the brick size variable, or you could add some other shape to it. I'll leave that to you as an exercise. But this is the fundamental steps that you need to create a very flexible segmental arch.
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