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In Rhino 4.0 Essential Training, author Dave Schultze shows how the 3D NURBS-based modeling tools in Rhino 4.0 are used to engineer products from toy robots to full-sized aircraft. This course concentrates on using Rhino 4.0 for industrial design and rapid prototyping, with a review of common 3D terminology using specific examples. Along with a comprehensive exploration of the Rhino interface, the course includes an introduction to building 3D objects with Rhino's three primary entities: the curve, the surface, and the solid. Exercise files are included with the course.
Next up, we will talk about the Mirror command and how best to use it. This command is ideal for any symmetrical geometry, whether it's a curve, surface, or even a completed solid. It's also a big time-saver, since you only have to build half or even a quarter of the geometry and let Mirror do the rest. Even better, it provides complete accuracy since you know that each side matches the other side. We will just start off by making a mirror copy of the robot arm, but it's important to have an axis setup. So, in this case, I have got this line down the center. Let's go ahead and maximize the Front viewport.
I am going to start the Mirror command by finding it under Transform > Mirror. Objects to mirror are the arm. Enter. Now, we are going to have to snap the two endpoints of that line or axis down the center. So, make sure your snappings are correct. I have got Endpoint, which will work. I'll snap here. And if I don't have another endpoint to snap to, it's very easy to let something misalign. So, let's snap to this endpoint. So, I know that this is copied, flipped over and exact equal distance on the other side of that Mirror plane.
Let's do it one more time with the leg. I will just select. I am going to right-click to repeat the command and just define the Mirror with the same two points. Let's check out the Mirror command on some curves and see how it works differently. I'm going to go to the Top viewport, maximize that, zoom out and then hide some curve geometry. I'm going to select this curve and do a quick Mirror command and then talk about some potential problems.
Just snap the two endpoints, and notice we get a kind of a pinch here. I will show you the reason why that can happen and how to fix it. The last two control points are not perpendicular to the axis. So, anytime that happens, you can end up with a situation where it'll pinch or out, and you'll probably want it to be a smooth flowing transition over the top. So, let's delete this other side and I'll show you the fix. I have drawn a construction line from one of the control points going in perpendicular to the axis.
We just grab the last point and make sure it aligns. So, I'm going to drag and it should snap to the endpoint. There. Now, these two are in perfect alignment. We will zoom out and repeat the command. I am going to turn control points off with F11. Start Transform > Mirror. Object, right-click to two points. So, those should now flow perfectly smoothly as if you've drawn them in this one single curve all the way through. Okay.
Let's show the next logical step where we have taken the curves and we are going to extrude them into a surface. I'll show you another tip. I go to the Perspective viewport and zoom in on these two curves. I am going to select them both and do a quick Surface > Extrude and talk about some potential problems. Notice the thick edge here. These are two separate surfaces because they were generated from two separate lines. So even if we join them together, which they will, they will still have a little bit of a kink, as small as that may be.
I'm going to show you an improved method. After a Mirror, it's one extra step, but it prevents this problem from having. Okay, so after the Mirror has been completed, we are just going to join the two lines, the Join command here on the main menu. I am going to turn the control points on. So, this is now one curve. You can even delete this point in the center that is shared from these two sides with only a minor modification of the surface. Let's turn the control points off and ere- extrude that one more time and check it out.
So, notice no seam and that should much smoother for the final project. Okay. Let's talk about a related command which is called Symmetry, which does pretty much the same thing as Mirror but lets you continue to tweak it and update the other side. I am going to start the command here by selecting the object, going to Transform > Symmetry. It's right next to Mirror. Now, in this command you need to turn on what's called Record History.
It's very easy to forget. So, you can do that before or after the command starts, and I am going to define the plane with two points. Now, it looks like that same things has happened, nothing different. However, when I select the curve, F10 to turn on the control points, the other side updates. Occasionally, you can't really visualize how the whole thing will look with only half the points selected. So, this will update both sides. We can even do the same thing with the surface in this next example.
I have got it off with the plane just to show how powerful it can be. Start the command, Transform > Symmetry, turn on Record History. Select an edge of this surface or curve and then define this plane one more time. We are going to snap to both points. Notice how it flows across and maintains perfect smoothness. Let's verify that by highlighting the finished surface and turning the control points on and see what we can do.
I will grab this point here and just kind of pull it around. You see the other side update. It might be easier if I grab some points back here. I am going to use the arrow keys to nudge them. It will continually update both sides and even move other points as necessary to maintain that perfect smoothness and continuity. Now, one word of warning. As soon as you move either the axis or the surface, you have broken the relationship.
You can actually go work on other parts of the model and come back here. And as long as the relationship has not changed, it will continue to update. So, the Mirror and Symmetry commands are both ideal ways to build symmetrical geometry quickly and with guarantied accuracy. The Symmetry command does give you the extra ability to continue tweaking while seeing the final result, but remember, once you move the part away from axis, the Symmetry connection is lost.
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