Join Dave Schultze for an in-depth discussion in this video Building a 2D gear, part of Rhino: Tips, Tricks & Techniques.
- [Instructor] This video we not only build a cool gear, but we also learn some very important lessons on strategy. Let's recap some of the points I mentioned earlier. We're always going to build with curves first, then generate surfaces. Building with curves gives us the ability to change the design much easier at any time. We're also going to try to avoid building stuff all at once, which means we just break it into simpler parts which you're going to see right here. The final tip I like to mention is I build things bigger and then trim them back if it's easier.
You'll see what I mean here in just a minute, we're going to start building this from several components and get the gear on the right. Let's zoom out and go down to the construction plane here. We're looking for a command called star, it's a polygon, we can find that over here on the main toolbar. If you click and hold, here are some of the other shapes, there's polygon star. I'd like to change the number of sides. It'll default to different numbers depending on who used the computer last.
I'd like you to type in 24 for this one. Now we can snap to the center to create this but if you don't have your O snaps on or the grid snap on, here's a really cool trick. Hit zero and that jumps to the origin. Notice I didn't have to type 0,0,0. One zero, enter, gets you at the origin. For the star, we got to give it two separate radii, so we can start somewhere here at the top, I'm going to hold down shift so it goes straight up.
Click once and then it's looking for the second radius, that's the inside and outside. This does not look like a gear but hang on, we're going to do two more curves here, both are circles. I'm going to go over to the circle command here on the main toolbar. We can snap to that origin if we have the snaps on or just do zero again, we have a lot of options. As we come up here you might accidentally snap to different stuff, if you want to avoid that problem just hit alt and then it'll ignore all the snaps for as long as you have alt pressed down.
There's the inside, I'm going to make one more, so just click on circle again, go ahead and snap there. This time I'm going to zoom in just a little bit. Right about there should be good. This looks like a big stinking mess, so what am I doing? I'm breaking stuff down into simpler elements. Imagine, if you will, we've got a gear. Here's one of the teeth, here's a little groove, coming back up, over, back down. See what's happening here? Now, this would normally require a lot of trimming, however, we're going to use a tool call curve boolean.
Again, we have to do a couple steps because this is a lot of stuff but I've only drawn three simple curves. What's the big deal with two simple steps? The trick is, it just takes a few times to memorize this. Let's go ahead to the curve tools toolbar and almost here at the end is the curve boolean, so select that. I did say we're going to do this in two passes, however, we got to make sure that delete input says all. When I do an operation like this, I just want the final result, not the components that went into it.
That would give me too many things. We just want to delete the input and only keep the output, that's what it's really asking. We're going to break this into two parts finally. I'm going to pick the gear, we're going to use that every time and we can start with the inside curve or outside. Let's do the inside circle here. Right click to say I'm done selecting. I could select in these areas, if you used the curve boolean command you know how it works, you can click in an area to add or subtract, however, that's a lot of clicking so if we want the inside a little trick I've discovered is click on the outside.
Watch what happens, I click one time, it zooms around and then I right click to accept. Let's turn that off and kind of examine. Instead of clicking in all the different zones, adding and subtracting, all you're really doing is giving it the fast path around. Sometimes you have to do it in the center and click a lot of times. But in situations like this, you can just click on the outside where the opposite parts you want to keep. That's a quicker path for the curve boolean command to trace. Okay, let's do it one more time. I can just pick both of these guys with the crossing window, go up to the curve tools toolbar, select curve boolean and since we want to keep the opposite side here I just come on the inside.
That looks like that'll trace the path I want, so just click, get kind of a highlighted area, it depends on your settings but hopefully you can see that, and right click to accept. I'll deselect, un-highlight that guy and we'll zoom out just a little bit. Now you can see the breaking things into steps, even though it initially seemed a little more complicated, was a way better way to do this. Otherwise, you'd have to build each of these teeth and array them in a polar array and then do a lot of complicated math.
Let's finish this up by putting one more circle here in the center, just for the axle and just for fun, we can pick those two curves inside and out, just to double check how cool this will look soon. My favorite surface command is surface from planar curves, and sure enough, that's going to work pretty well when we wrap it up. Even though we just made a really simple gear, this demo has touched on several very important steps shown here in the workflow list. In the next video, we'll continue work on the gear in 3D.
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Skill Level Intermediate
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