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In this lesson, we are going to create the socket that connects the handle of our wagon to the front axle plate. While creating the part, we are going to learn what NURBS surfaces are and how we can press and pull them into free form shapes. We will also take a closer look at how to use the Patch tool as a means to close a hole or cap a surface. There are two types of surfaces in AutoCAD: procedural surfaces, these are the associative type surfaces we have been creating so far, and NURBS surfaces. NURB stands for Nonuniform Rational B- Spline and a NURBS surface is what you would use to create an organic freeform shape.
To create a NURBS surface, I am going to click the NURBS Creation toggle in my ribbon. As long as this toggle is turned on, every surface that I create from this point will be a NURBS surface. I would like to start by revolving this arc around this cyan axis. So I am going to launch the Revolve command, I will select the arc and hit Enter, and then I will select these two endpoints to define my axis of revolution. Finally, I will enter a value of 360 and hit Enter. Now, if I hover over this object, we can see that's it a NURBS surface.
NURBS surfaces are non-associative. Their shape is determined by control vertices much like a spline. By default, the control vertices are not visible on screen. If I want to turn on the control vertices for this surface, I am going to click the Show CV button in the ribbon. I will then select my surface and hit Enter. Let's back up a little bit, and I will center this on screen. Each of these control vertices represents a handle that I can use to push and pull this surface into whatever shape I like.
To make a change, I can click on a vertex and then I will hover momentarily till my Move gizmo snaps into position. I can then select an axis. In this case, I am going to select the Z axis and as soon as I go to make a change, AutoCAD brings up a warning. It says, you know what, if you want to edit these vertices, you are going to have to rebuild the surface. Notice that AutoCAD is requiring a degree 3 in both the U and V directions. But don't worry, this is quite common. It happens a lot. Let's click Close.
We will close up the warnings and my part is still selected. To rebuild this, I am going to go back to the Control Vertices panel and I am going to click the Surface Rebuild icon. As you can see my surface had a degree 2 in the U and V direction. AutoCAD has already fixed that for me. Up here, I can set the number of vertices that I'd like in the U and V direction. I would like to use 5 vertices in the U direction and 8 vertices in the V. When I am finished entering values, I will click OK, and notice the difference.
I am going to orbit this up just a little bit and we can see one, two, three, four, five vertices going left to right and I have eight vertices going around the outside. I am going to tip this up just a little bit. I would like to make a change to this topmost vertex. I am going to click to select this. As soon as my move gizmo snaps into position, I am going to select the Z axis and I will pull this up a height of 2 units.
When I am finished, I will hit Escape to deselect. We can use that same workflow to adjust any of these handles around the outside of a surface. If we like even more controls, I can add or remove vertices if I like. Notice in the Control Vertices panel, there is a tool right here we can use to add. We can use this one to remove vertices. If we look right here in the Control Vertices panel, I've got a tool that I can use to add vertices, and one that I can use to remove them. I would like to demo the tool. I am going to click Add vertices.
I will then select my surface and notice that the tool's not working that well. At the time of recording, AutoCAD has a bug that's preventing this tool from working like it should. I am going to hit Escape to cancel out of the command. Let's back up a little bit. I am going to pan over. Notice I have another surface over here. If I select this surface and turn on the control vertices, we can see it's essentially the same thing. I am going to select Add control vertices again. I will select this surface and notice that as I move my cursor around the outside, I can add a new row of control vertices wherever I like.
If I right-click, I can select Direction and I can change the direction of my row. Now I am going to turn off my running object snaps so these don't get in the way, and then I am going to click right here to place my new row of vertices. At this point, I can select any of them. I will then select an axis on my gizmo and I can pull or push this and place the vertex wherever I like. Once again, when I am finished I will hit Escape. Let's remove some vertices this time.
I am going to click the Remove tool. Once again, I will select my surface. As I go back and forth, I can select a row of vertices that I would like to remove. Let's remove the row that we just added. To do that, I am going to right-click, change my direction. I will then move to that row and click and those vertices have been taken away. If we would like to make an even more precise edit to our surface, we can use the CV Edit Bar. If I launch this command and select my surface, as I move around the outside of the part, I can see these two red lines that form a cross.
I can use this cross to place a vertex at any specific location that I like. I am going to click right here. Once again, I am going to select my Z axis and I will pull this vertex up. Notice there is another circular grip over here. If I click this, I can adjust the magnitude of my change. Once again, I am going to click on screen to set the magnitude and when I am finished, I will hit the Escape key. Why do those changes work nicely here, but not over here? It seems the farther our part is away from the origin or the 0,0 coordinate, the more difficult it is for these commands to function and you may be asking why didn't we just draw it over at the other location.
Well, every part we have drawn so far has been created at the location where it's needed in the final assembly. This way, when we assemble our components later, each of them will drop in where they belong. Now I do have a workaround. If you happen to be working on a surface that's a distance away from your origin, and you want to add some vertices, I am going to click to launch the command. I will select the surface. Notice it's not working but if I back up far enough, all of a sudden it does start working. I will zoom in a little bit, AutoCAD gets scared and it stops. Zoom out and it starts working again.
Now I don't want to add any more vertices, so I am going to hit Escape to cancel. I will zoom in a little bit. Since I am finished working with the vertices, I am going to turn them off. I can do that by clicking the Hide CV button and at this point, I would like to close up the holes on either end of the surface. To do that, we are going to use the Patch tool. I will click the icon to launch the command. I will then select this edge and hit Enter. And notice that the Patch tool has the same settings as the Blend tool.
We can adjust Continuity and Bulge Magnitude. Now by default, my Continuity is set to G0 so I am getting a nice flat cover over this hole. If I was to set this to G2, we can see that AutoCAD creates a nice rounded cap to cover the hole on that surface. Now in this case, I am interested in a flat patch. So I am going to right-click, set my Continuity to G0. When I am finished, I will hit Enter. Let's orbit this around. We will do the other side.
I will launch the Patch command. I will select this edge, and hit Enter, and I will accept the default Continuity of G0. Now notice as soon as I am finished with this command, if I select this surface later, there is no grip that I can use to adjust the continuity. Remember that NURBS surfaces are not associative. Once they have been created, the only way we can edit them is by using is a control vertex. I am going to hit Escape to deselect. I'll orbit this back around. I would like to drill some holes in this object.
I am thinking the easiest way to do that would be to convert these surfaces into a solid. So I am going to launch the Surface Sculpt command and I will select my three surfaces. Since these surfaces form a watertight volume, as soon as I hit Enter, AutoCAD converts this geometry into a solid. Let's turn on a layer. I am going to go to the Layer Properties Manager. We will turn on the solid_extrude layer and then we will return to the drawing.
This geometry represents the holes I would like to drill in this part. I am going to be using the Extrude command and since these will both be solid extrusions, I am going to set the Solid tab current. I will start by launching Extrude, I will select this circle, and hit Enter and I am going to extrude him through the part at distance of 3 units. I will launch the Extrude command again, and I will select this circle and hit Enter and I am going to extrude him down a distance of 3.4.
To remove their volume from the part, I am going to launch the Subtract command. I will select the socket and hit Enter, and I will select the cylinders that represent holes and hit Enter and as you can see, their volume has been removed. Now that I am finished with the geometry, I am going to go back to the Layer Properties Manager, I am going to turn off this solid_extrude layer, and the surface_ revolve layer because I don't need to see that geometry anymore. Let's go back to the drawing. I am going to back up and I am going to erase this extra surface so that there is no confusion later.
To do that, I will select it and hit the Delete key on my keyboard. Finally, let's save this geometry so we can use it in our final assembly. I will click the application menu and I will select Save As. We will save this in the exercise files folder inside the finished_parts directory and I am going to call this socket_finished and I will click Save. This completes the geometry for the socket. In this lesson, we learned that AutoCAD produces two types of surfaces, procedural and NURBS.
We learned that NURBS surfaces have control vertices that can be used to press and pull surfaces into freeform shapes. We also learned that the Patch tool can be used to close a hole or cap at the end of a surface and it uses the same Continuity and Bulge Magnitude setting as the Blend command.
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