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In this lesson were going to create the rear bracket for our wagon. While creating this part, we will learn how to produce a smooth transition from one surface to another. And we will also see that we can trim our surfaces using two-dimensional line work. On my screen I have got some polylines. I'm going to orbit my drawing a little bit, so you can see their context in 3D space. Generally speaking, I've drawn the lower edge and the upper edge of my bracket. I am going to start out by extruding this lower edge up. So I'm going to launch the Extrude command.
I will select the edge and hit Enter, and then I'll pull this guy up 8 units. Let's zoom in on the top, up here I've got a closed polyline, and I would like to create a flat surface based on this geometry. To do that I'm going to come back to Create panel, and I'll launch the Planar Surface tool. This allows us to create a flat surface based on points that we click on screen, or by selecting an existing object. Since I have an existing object, I'm going to right-click, and select Object from the menu.
I will then select my closed polyline, and I'll hit Enter. This surface will now represent the top of my bracket. At this point I don't need my polylines anymore, so I'm going to turn that layer off. I am going to open up the Layer Properties Manager. Mine happens to be anchored to the interface. If yours is not, you can always type LA and hit Enter to turn it on. I am going to turn off the Surface Section layer. I'll let the palette collapse, and at this point I would like to create a nice smooth surface transition from the edge of this surface to the edge of this one.
To do that, I am going to use the Blend tool. We can find Blend in the Create panel on the ribbon. I am going to click to launch the command, and then I will select my first set of edges. I'll grab the three edges at the edge of this surface, and I'll hit Enter. Now I will select the second set of edges. I'll grab this one and this one and this one. Generally speaking, I am just was going to work my way around this object. Now I don't want all of them. I basically want to get these two sides.
When I am finished selecting, I'll hit Enter, and AutoCAD creates a nice transition between those two surface edges. Technically we are not done. We are in a Preview mode right now. We can still just the shape of this transition by modifying these settings. We have CONtinuity and Bulge magnitude. CONtinuity measures how smoothly our surfaces flow into each other. Let's adjust that setting first. I'm going to click to select. Basically we have three options, G0, G1 and G2.
G0 represents no smoothing. Basically it's an angular transition between the surfaces. G1 applies some smoothing and G2 applies the highest amount of smoothing. Now one thing to know. When we adjust our CONtinuity, we will be adjusting it twice. Once for the first edge, which is located right here, and then we will have to set it again for the second edge up here. I am going to select G0 first. Then I'll select it again for the second edge, and notice the difference. My surface transition is very angular.
Let's go back to CONtinuity. This time I am going to set each edge to G2, to get the maximum amount of smoothness. And you can see the difference. Let's talk about Bulge magnitude. This sets the roundness of the blend where the surfaces meet. And just like CONtinuity, we will have to set this twice. By default out Bulge magnitude is set to .5, and acceptable values are anything from zero to one. I'd like to have a pretty large curve in my transition from my first edge, so I'm going to set my Bulge magnitude to 1 and hit Enter.
And then I would like to have a nice tight radius on this upper edge. So I'm going to set the second Bulge magnitude to .2. And you can see the result on screen. Once you've dialed up your blend such that it looks exactly the way you want it, you can hit the Enter key to accept. Now at any point in the future, if you want to come back and change these settings, you can simply select this surface and notice we get a pair of grips. Generally speaking, we have one grip that controls each edge. I am going to select this one.
From here I can change my CONtinuity. I'm going to set this to G1, so we can see the difference. I will then select this grip, and I'll set this one to G1. When I am finished I'll hit my Escape key to deselect. You may be wondering how can we change our Bulge magnitude after the fact. Once again select the surface, and if you hit Ctrl+1 to bring up your Property Changer, right down here in the Geometry Settings, you'll find your start and end Bulge Magnitude. Notice we can also change our continuities from here as well.
I am going to leave these settings the way they are, so I will close my Property Changer and then I'll hit Escape to deselect my surface. Let's try something else. I'd like to go to our right side view, so I am going to click the right side hot spot on my ViewCube. And then I'm going to zoom in on the lower end of my bracket. Then I'll go back to the Layer Properties Manager and I am going to turn on a layer called Surface_Trim. On this layer I've drawn some geometry that I would like to use to trim this surface. In AutoCAD 2011, surfaces can now be trimmed.
To trim this surface I'm going to come up to the Edit panel and launch the Trim command. I will then select my surface and hit Enter. I'll then select my cutting edge and hit Enter. And then I'll click to select the area I'd like to trim. When I am finished, I'll hit Enter. Let's turn on another layer. Once again we'll go back to Layer Properties Manager. This time I am going to turn on the Surface_Hole layer. Let's use the Trim command to drill a hole in our surface. Once again I'll launch Trim. I'll select my surface and hit Enter.
I'll select my cutting edge and hit Enter, and then I'll click the area I'd like to trim. When I am finished, I'll hit Enter. Now I have one more hole I'd like to put in this bracket and that's up on the top edge. So I am going to come over to the ViewCube and I'll click this small triangle to switch to a top view. Let's zoom in on the top of the bracket, and once again, we will use the Trim command to remove this hole. Trim, I'll select my surface, and hit Enter, cutting edge, Enter, and then I'll click to remove the surface.
I am going to zoom out a little bit. Let's adjust our view in 3D space. Now that our part is finished, I'm going to turn off some unnecessary layers. Let's go back to the Layer Manager. I'll turnoff all of these layers that start with surface, and finally let's save this part so we can use it later in our finished assembly. I'll go to the application menu. I'll click Save As. Let's go to the Exercise Files folder. We will open up the Finished_Parts directory and I'm going to save this as rearBrackets_finished.
This completes the geometry for the rear bracket. In this lesson we learned how to use the Blend tool to create a smooth transition from one surface to another. We also learned that we can control the appearance of the transition using settings that adjust the continuity and Bulge magnitude. Finally, we learned that our surface objects can be easily trimmed using two-dimensional line work.
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