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In this video, we'll review the three different ways to create solid geometry mostly from existing entities. Rhino calls these resulting objects solids, but you may also be familiar with the term primitives from other 3D software apps, which I'll use interchangeably. A reminder on the terminology: a solid created using these commands ideally results in a finished and completely closed entity, but you're always free to build a solid one curve or surface at a time. Okay. Let's spin around the backside here and take a look at some of the setups.
We're going to build a jet pack starting with curves then some surfaces and some solids. Let's take a sneak preview at what the jet pack might look like. So, there's our twin engine rocket pack. Let's turn that back off. We'll start in reverse order. I am going to end up with the solid from curves, which is actually the recommended method, and you'll see why in just a minute. Okay. And let's go to the Solid menu and select Cylinder and I've got my Intersections snap on here. That's a no snap.
So, we can go right to the center of those two lines, and I am going to type in some numbers here just so everything kind of looks consistent. So, I am going to type in for Radius 10 and then of course, you can always move it up and eyeball the final height. I am going to go ahead and type 40. So, we've just made a cylinder primitive. That's the quickest and easiest way but also is the most restrictive as far as going backwards in time.
Let me show you a quick example what might happen if I were to delete this or make a change to it later. Unless I had remembered the radius and distance, I could not regenerate that and resume work. So, that's why I recommend that you start from either a curve or a surface. Let's check those out. This is a flat plane that happens to be round. So, we'll check out Solid > Extrude Surface > Straight. I want to just click that one surface, hit right-click to enter and go up, again typing in 40, just the old match.
Now one quick note here. That surface, which used to be separate, is now joined and we have an additional copy of it on the bottom. So, let's try it with another surface that is not flat on the construction plane. Solid > Extrude Surface > Straight and I'll type in 40. You notice that it works just as well, the key being here that the original surface was on a flat plane, so it can only be extruded forward or backwards in a single direction but not a problem.
Here is where it gets a little bit tricky. I want to pick a deformed surface. It does look like a circle from the top view. Let's repeat the command again, Solid > Extrude Surface > Straight, and now since that originating or generating surface was bent, Rhino is just defaulting to the construction plane, so the extrusion just goes up vertically, and I'll type in 40 again. Let's see what we get. So, it does close it off, but that cap is not attached.
All right. Let's look at the final case where we create from curves. This is the recommended approach. Let's take this curve here, highlight it go to Solid > Extrude Planar Curve > Straight, type in 40. So, now we have a completely enclosed solid form and notice we have the curve still there separate. It's not included in the set. It's not joined together. That is ideal if I ever make any changes to this or throw it away and start over.
I've got that curve and so I don't have to remember what its exact radius was. I just have the existing geometry there as reference. It's always the way to go if possible. I'll just do one more Extrude Planar Curve > Straight, not a problem since it was on a flat plane, but here is our bent shape just for comparison. So, I've got a seam on there. Let's see what happens. Solid > Extrude Curve > Straight.
It said planar curve, but it looks like it's still working. However, when I go up to 40, I wasn't able to cap it. So, you can see the difference here. This was a single flat surface, and that's just not possible since this curve is bent. It would actually be two. So, the best it can do is go up vertically from the construction plane and then it ends up being open, so you would have to manually close that off. So, the Solid commands are very simple and fast to work with, but they can quickly introduce limitations if you're concerned about the ability to reverse or undo multiple complex steps or simply just explore multiple design options.
So, if that's the case and you still prefer to use solids, then try to build from curves, since you have a record of your construction geometry, and then you can quickly regenerate your forms if there's a change. And you know it will change!
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