From the course: Meshmixer Essential Training

Using CAD models in Meshmixer - Meshmixer Tutorial

From the course: Meshmixer Essential Training

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Using CAD models in Meshmixer

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Okay, so here is one gotcha when you want to go from parametric CAD modeling into Meshmixer. I modeled something here in Fusion 360, the parametric program. Just kind of like a little pedestal, or maybe a little awards statue and I might want to put something organic on the top. So, I want to bring this into Meshmixer and start working with it. So this is great. I go into bodies here and export as STL and I'm going to send it directly into Meshmixer. So I click OK. So after a second, Meshmixer comes up and we get the object right here. So good enough. We start going into the sculpt tool, maybe with a draw brush. Get it nice and big and start working and the entire model just starts to blow up the moment we touch it. It didn't blow up as much here, but I'll tell you why. So I'm going to undo this. So this model, if I hit the W key for wireframe, you can see that, it may be a little bit dark. So, I'll go in. When your model goes dark like this, sometimes you have your object not selected, so you go to show objects browser and make sure that your object is selected. So you can see up here that we do have a lot of triangles and down here we have no triangles. And because Meshmixer wants to work with a lot of triangles, when you hit it with a tool like the sculpt tool, I'll turn flow off. Even at a low strength, it only has two triangles to work with, so it starts to do weird things. It changed the entire three faces at the bottom because it only had two triangles and because I have refinement turned on, it starts to add them, but adding more triangles when you only have two to start with, ends up making huge changes to your mesh. If we try to do this up here, the triangles are a little bit more dense. But even up here, you start to get weirdness happening because I if undo this, these triangles go all the way from this side all the way down here. Even though they're skinny like this, they encompass the entire face, so trying to make a change to one triangle ends up changing your entire face like this. And you see this a lot in models that you download from online websites that are created in parametric CAD software. So, there's a very, very simple trick to get around this. You need more density inside of this. And then click on select and hit control A to select everything, or command A on a Mac. Everything is selected. We'll go up here to edit to remesh and you want to choose linear subdivision and what linear subdivision will do is it divides the triangles that are already there into smaller triangles. So it doesn't change the shape at all, it just adds more density inside. So you're still going to end up with triangles, but you're shape isn't changed. If you did something like relative density or adaptive density, even if it's very very turned up, you end up with kind of weirdness here. So what we're going to do is go to linear subdivision and turn it up as high as it will go. And what this will do is remember these triangles went from this side to this side, now you see that you have a band here, a band here, a band here, you have a lot more triangles to work with that don't go from face to face. So I'm going to click accept and clear selection. So now, we have all of these triangles here. You still have some discrepancies, you have this being very very dense here and not here, but if we click on the sculpt tool, we have a little bit more of a chance for the sculpt tool to have a known effect. You know obviously this is maybe smoothing out these hard edges a little bit more than you might want, but it's not destroying the entire mesh like it did before. Now I'm going to undo that. And I'm actually going to undo all the way back to where it was to start off with. So one other trick you can do. If this is something that you want to keep and this is something what you want to keep, but you want to make the subdivision only happen on certain surfaces, there's a couple ways to do it. If these are very easy like this, you can always go into the select tool, make your brush small, and then just click and drag to select only these meshes and the two bottom ones and then run the remesh tool with linear subdivision. So it ran a lot faster and we're not touching the top of the mesh at all. But, if your entire object, you want to remesh in a more kind of known fashion, you can also go up here to edit to generate face groups. So what this will do is it will split based on angle threshold if we turn it down everything because it's on face group, but we don't want that. We want to turn this up, so that all of these contiguous areas are all their own face group. I'm going to turn this down until we get a little bit better result right here and now we have these as all face groups. So I can go into select and then just double click on this and it will select that entire face group. Or, if I go into select and double click on this green, it will select just that face group. So, that edit, generate face groups command can be very good to segregate your mesh and now I can go in and just work on individual areas to subdivide them if I want. So that's what happens sometimes when you bring in parametric CAD models into Meshmixer. You need to actually add a complexity before you can successfully work with them.

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