Complex Topology and Class-A Surface Modeling with Inventor

PAUL MUNFORD: Good morning, everybody. Thank you very much for coming along. This is Thursday morning, so this is the last day. So it's really good to see so many people here.

OK. So this class is Complex Typology Class A Surface Modeling with Autodesk Inventor. Just to quickly do a class summary, so this is from hack and whack to planned and perfect complex topology. And learn the objectives here, how to use the language of curvature continuity with confidence, discover some of those hidden away software surfacing tools, building complex topology from individual surface patches, and converting surfaces into a solid model.

But on top of that, what I really want you guys to get out of today is the confidence to go ahead and play with this stuff. This is only an hour and a half class. I really can't cover everything about surfacing. But I want you to have a bit more of a theory so you can go and try these things out and practice and then give me some feedback, and let me know how you get on.

So just to let you know a bit more who I am, My name's Paul Munford. I'm an application engineer with a company called Graitec. We're an Autodesk reseller in the UK. And I've just been to Graitec for about three months. I actually just started off on the tools as a carpenter and building scenery for TV and film.

I did that for eight years, and now I moved into the drawing office and learned Autocad, and spent 10 years with Autocad and Inventor in the construction industry doing woodworking trades, joinery, and mill work, and that kind of stuff, and the last three years as a CAD manager. And I'm a big CAD geek. In my spare time I write for AUGIworld Magazine, Develop3D magazine. And I just finished a book, Mastering Events 2016 for Wiley, which comes out in December.

And I've also done some training courses for Infinite Skills. And in fact, this class seem like a father class of Infinite Skills. I'm just trying to pack it all down into an hour and a half to give you a good indicator of it.

I'm going to try and do as much theory as I can in the first half of this class. And the theory really is applicable to any software. So whether you use Inventor, whether you use other software tools, hopefully you'll get something out of that. Second half of the class is going to be a bit more demo.

So I'll be up in the machine. I'll be showing some stuff inside inventor. I'm happy to keep it a bit of a dialog. So if I do you go fast, or if you want to see me do something again, then just shout out.

OK. So what is surfacing? So surfacing modeling is creating kind of more organic shapes, industrial design. And it's a method of modeling using surface patches. We create one surface at a time. And a surface, what is a surface?

A surface can be considered to be an infinitely thin skin stretched between boundary geometry. Typically surfaces are open, but we can close them off once. Once we close them off, we can turn them into solids. So a solid is an enclosed volume completely surrounded by faces that can then have Information attached to it, like weight or mass and that kind of thing.

I also want you to define difference between prismatic and nerve surfaces. So prismatic surfaces are pretty much built out of lines and arcs. And prismatic modeling is what most people do with [INAUDIBLE]. It's a standard thing. So it's rectangles, circles, pyramids, that kind of stuff.

The last example over here would be considered a nurb surface. So a nurb surface is a surface built from splines. So why inventor? Well, I have to say, if you're really interested in surface modeling, you don't use inventor.

You'll need something like Alias. This class is really aimed at people who either don't have access to something like an Alias, or don't have time to learn it, or who pretty much 95% of the time you're very confident modeling with Inventor. And it's just that last 5%. It's just that kind of, when you get something a bit more complex, you're not quite sure where to start, which is why I want to cover so much of the theory because I really want to give you guys a sort of grounding, and how do I start, where do I start? So we use Inventor because that's what we got.

OK. So let's begin with a bit of theory about surface continuity. So when we're doing organic shapes, it's all about the smoothness, particularly where the shapes join at the seams. And where they join, that's called surface continuity. And that's the first thing they're going to look at and try to understand.

So curvature continuity is measured in units of g, which I believe just stands for geometry. So typically, if two lines aren't circles, if they don't touch, then there's no g. There's no continuity between them at all. And I think of that like this.

You can have beautiful curves, they can look really great, but if they don't touch, you got no continuity. So the first degree of curvature continuity is touching. Usually, we're talking about G0, we're talking about something that comes to a sharp point. And you can see here the constraint we would use in Inventor to create 2D curvature continuity between two curves, would be a coincident constraint.

And I kind of think of that like this. So it's usually sharp curves, the kind of stuff you'd get with your prismatic modeling. Now, as we go through curvature continuity, what we're doing is we're matching information between the two curves. So we have to have touching to be able to have curvature continuity.

But as we start to match, we start to match properties. So the first property we're matching would be the Tangent Property. So the two curves are tangent to each other. And we call that G1. So one property is matching between the two curves.

So I think of that like the Batman car. This is in the Michael Keaton Batman, when the grappling hook comes out the side of the car, and grabs the lamppost, and it spins 390 degrees. So G1 is usually considered to be kind of engineering fillets.

So when you put a fillet on the sharp edge, and you get that tangent continuity between the sharp edge and the fillet, that's G1 continuity. The next one we would match up is curvature. So what we're matching here is we're matching the degree of curvature at the point where the two things meet.

OK. So if we had two arcs, the curvature would be consistent. In this case, we're doing spline. So the curvature can change along the degree of the spline. But at the point they meet, we got the same curvature. And just to backtrack slightly, I've got a tangent constraint on the last one. This one I'm using a G2 constraint.

OK? I've turned on the curvature cone here so you can see the degree of curvature on these two splines. And we know the degree of curvature is the same because the height right here is the same. So where those two curvature cones come in, we got the same degree of curvature. And I think of that like this.

This is like a race car with smooth curves coming in and out, smooth accelerations that goes around the corners. And this car's from Battle of the Planets. I used to watch them as a kid. And I was surprised to find it's actually called a G2 car. So that was pretty cool.

So the last degree that we're going to talk about today is acceleration. Now actually, you could continue matching properties. But realistically, G3 is as far as you would usually go in surfacing. And in fact, there is no G3 constraint in Inventor. So we can coax G3 out of inventor by careful manipulation. But it's not a standard out of the box thing.

So G3 matches. It's touching, it's tangent, it's got the same curvature where the two curves meet, and we have the same acceleration. And acceleration can be thought of the degree of changing curvature. So right here we start off with not much curvature where it's pretty straight.

And as we go up we got more and more curvature. And here we can see that the curvature cone graph here is tangent at the top as well as the two lines being tangent. Now, that tells us we've got G3 curvature continuity. And again, the only way you can get that is by manipulating that spline until you get that curvature continuity.

So I think about this. This is super smooth. This is as smooth as you can get. Now typically, you only really want G3 on some of your most important surfaces. So it's not something you're going to be doing all the time. But you can get it.

OK. So that was 2D curvature continuity. But the same rules apply with 3D curvature continuity. So we can see here again, G nothing. They're not touching. There is no continuity. G0 G-0 is typically touching but shark. G1 will be tangent. G2 is tangent plus curvature. And G3 is tagent plus curvature plus acceleration.

OK? So that's how we understand whether we've got smooth curvature in our model or not. OK. So I'm going to move onto another important concept. This is topology versus Geometry. So topology can be thought of as a number of faces and edges there are in your model. Geometry is the shape.

So on the left-hand side, I've got two surface models that have the same topology, one face with two seams there, one seam on the bottom and a seam up the side. On the right-hand side, I've got two models with the same geometry but different topology. So one has this seam going up the side and one is seamless.

OK. So we all know from the normal prismatic modeling that we do, that the same shape can be built in a number of different ways. So the way we describe that is using a number of different kinds of topology. And given the same shape, we probably will go-- probably in this room we'll all have a different approach. But it's worth thinking about your topology before we start the model.

Here's another important concept. And this is all stuff that I'll be using as I go through because I just want to make sure that there's a level of knowledge in the room. So I apologize if you know this stuff. But I can't assume that everyone knows it, so I'm going to just step through some of these words.

So this is surface normals. So the normal direction of a surface is really it's front and its back. And the normal direction can be thought of as a vector. A vector's coming off perpendicular to a surface. Now it's a little bit easier to see with work planes. So you may have noticed work planes have a distinctive, like usually an orange side, and the back side of it's blue.

So the orange side would be the face side. That's the normal direction of that work plane. Surfaces in inventor don't usually have an indicator of which side is the normal, which side is the face. You can usually tell. For example, if you thicken something, the direction it goes in is the normal direction. If you extrude some geometry, then it extrudes, that's the normal direction of the work plane that the sketch was hosted on.

OK? So again, it's just worth thinking about normals. It's worth thinking about how your faces, which normal direction you've got in your faces becomes important when we stitch them together later. OK. So this concept is called isoparms. Now, what you don't see in Inventor is you don't see how Inventor calculates surfaces. So I've tried to indicate that here using this analysis, this curvature cone analysis.

Isoparms are a grid. So inventor actually mathematically calculates surfaces as a grid. And it's a mesh square. OK? So this grid-- like in Autocad, you'd have Cartesian coordinates, x and y-coordinates. This grid for isoparms are known as Us and Vs. It's just the U and V direction of this grid.

But what's important to recognize is that inventor will always use a four-sided patch, so always a four-sided patch. So on the left-hand side here, we have a surface with a bit of a problem. You can see some of these patches don't have four sides. But in fact, they do. They are diverging into a single point.

That single point is known as a singularity because we have an edge in there, and everything calculated about that edge is being calculated as a 0 value. And not just Inventor, but any CAD system has a problem doing multiplication division of 0.

So you can build surfaces with singularities. And if that's your only surface in your model, that's great. But if you try and build more surfaces of that, you may have an issue. So I'll show you some techniques later to get around that. So that's isoparms.

OK. So there are a few things, a few phrases I'll be using I want to make sure everybody knew. So I'm going to talk briefly about patch layout. So when we're looking at something we'd like to build using surfacing, some we got to get smooth, surface continuity, the first thing we can think about is the theoretical sharp edge. So we can imagine when we take a square shape, and we apply a filet to it, the theoretical sharp edge is where the edges would have met before we applied the fillet.

So if it's something like this, the theoretical sharp edge would be somewhere right there. Now typically, it's a good idea to build to the sharp edge and then trim it back. So we got the edges, the theoretical sharp edge where they would meet. And then we can think about the blend line, so if we did a blend across that sharp edge, so we trim the surface back and apply a blend in there, where those blends need to start and finish.

OK? So one thing I struggle with in the past from the surface modeling is trying to put the blend lines in first, build the surface patch, and then blend. And that's just quite tricky to do. So I recommend you build to those theoretical sharp edges, then trim them back, then apply the blend in there.

So one more thing to think about after that, so typically you'd have three types of patches. So I'd say this is a primary patch. This is the first patch we're going to build. And we can build this without reference to anything else.

So typically, this might be a couple splines that are swept. And we could trim it back to make it that shape. Next, we'd have secondary patches. So these we've drawn up to that theoretical sharp edge. So secondary patches are patches that you have to build using existing geometry. You can't build them first, because you need to build a primary patch first.

And then the last set of patches would be the tertiary patches, which are usually those blends. So when we've trimmed them back, then we blend between the two. And there's one more, construction surfaces.

So one limitation in inventor, if we create a line in a sketch, and extrude that line, we can't apply any continuity or tangency to the sketch plane. So we'd have to apply a surface going in the other direction first and use that as a construction surface. So it's a surface that may never appear in your model. And you'll just put it right in there so you can use it to create tangency.

And one last tip on thinking about your patches and planning your model is flow. So it's keeping your loft so your sweep's flowing in the same direction. So again, those isoparms are all flowing in the same direction. So they match up nicely.

If you sweep things in different directions, again, you can have issues trying to get continuity. So it doesn't really matter whether you go one way or whether you go the other way, as long as it's consistent. So that's just a tip, help you out there.

OK, so creating surfaces. So how do we create a surface with Autodesk Inventor? Well actually, you'll find the surface option just about everywhere. It's not the standard. If you create a closed profile with Inventor, it will create a solid. And a solid really could be thought of as a short cut. It's a collection of surfaces that have already been trimmed and stitched together into a solid.

If we have an open profile, that in most cases Inventor will by default pick the surface option, not always, but most of the time. But you can override it. You can choose it yourself. And then you can create your surfaces. So most commands here you'll find here have got a surface option in it. So you have to make sure you pick it.

The thick and offset one, just take a look at that one, kind of come back and talk about that in a second. So that's it. You found them everywhere. Editing surfaces, well, most of the surface edit tools are in the surface panel of the modeling tab. So we have the trim surface. So that allows us to trim a surface to a sketch or to another surface.

Split face. So split face works on surfaces too. And don't forget that a surface creates a surface body in your model. So you can use body commands as well. Thick and offset we just scoped out earlier, could be thought of as copying a face. So if you thick and offset a face, choose a surface option, set it to 0, then you'll [INAUDIBLE] and copy that face.

Now, do have copy object in Inventor. But if you copy object, its non-associative to the underlying geometry. So when you change the underlying geometry, that surface won't update. If you use a thicker option, you can create a copy of a face that will update to the surface geometry underneath. So it's not something you would see. It's not intuitive, but it's a little tip.

So again, a surface will create a surface body. And you can operate on that body with some of the body commands. So if you want to move a surface, you can move a surface with the Move Body command. You just have to make sure you pick the body and not the surface. The Extend command-- so I go back in some of these tools here in the surface panel. The Extend command allows you to extend the surface. So you can select the edges and extend it. It's like untrimming it. So it's the opposite of Trim.

And then Rule Surface, so Rule Surface is new in 2016. I don't know if you have seen this one. So a Rue Surface allows you to select an edge of an existing surface and then create a surface of it off it that can be tangent or can be perpendicular to the edge. So that saves your hand to do it, like a line, and a sweep, and a 3D sweep around a curve. So that's a really helpful tool.

And the last one that could be thought of as a surface in too is Delete face. Now, one of things you'll notice, if you create a solid body in Inventor, you'll see a new body appear in the tree. If you delete a face, you'll see that body turn from a body into a surface body.

So by deleting a face, it's now open. It's no longer an enclosed volume. So even though it's gray, it's a surface. It's not a solid anymore.

Surfacing continuity tools. So again, these are kind of hidden away. A lot of people don't know they're there.

But in fact, in a lot of places, if you click on this little fellow at the end here, you'll have options to create curvature continuity between curves. And again, you'll notice we have G1, and we have G2. There is no G3. So if you want to create a G3 super smooth curvature continuity between services, it's all about how you create those splines that you then are going to build the services from.

OK. So that is a lot of the theory I want you to talk about. So it would helped you plan a more complex model. You can look at it in terms of its sharp edges, in terms of where you're going to put your blend lines in, in terms of the blends you're going to use, and some of the things that you think about in terms of curvature continuity.

So I'm now going to jump up here and start demoing stuff. OK. So there are two kinds of splines at Autodesk Inventor. There's the interpolation spline, and more recently we've got the CV spline. So I'm going to show you how these two things work.

So I will double click into this sketch. And you'll find the Interpolation Spline command up here tucked on the line. This is 2016. Sometimes the UI elements move around a bit. So I apologize if you're in a previous issue of Inventor. But this is 2016.

So I'm going to create an interpolation spline. And here's a tip. I recommend that when you create interpolation splines, you make it as simple as possible. So interpolation spline will create a curve between two points. Now we've created this curve, actually, we can apply curvature continuity to it using constraints because I'm using the G2 constraint there. And that is the best curve that Inventor can give me between those two original straight lines.

So I don't need to add anything else in there to get a nice blended curve. If you did want to add an additional fit point, just right click and choose Insert Point. There we go. And that will allow you to insert an additional point in there. And now you have a point that you can manipulate and move around to change the curvature.

You also have the option, if we right click somewhere near that point, we choose Activate Handle. When we activate the handle, that means we've got this handle that we can grab and pull and manipulate and push and pull around. And you can also dimension that point. You can dimension that handle.

Typically we do surface modeling, it's kind of underdimensioned or underconstrained, just because if you try to constrain every fit point in the spline you'd be there for a long time. So that is a lot different prismatic model. We like to lock everything down.

We also have the option here if we right click again to get a curvature handle. And the curvature handle allows us to adjust the degree of curvature around that point. And both of these I'd say can be dimensioned. This one is dimensioned. You can see it's a unitless value. So the highest that can be is 1, is a percentage of 1.

The curvature handle isn't just a radius. You've got to turn off the curvature. So here's a helpful thing. Sometimes when I'm working with interpolation splines, I can get out of control. So I just wanted to show you there's an option here to reset the handle or reset all the handles. And if we click that, it just goes back to the best degree of curvature we can get again.

One more option we have, if we look at the display curvature, so this is the curvature cone graph that I showed you earlier. So if we click on this, we can see what kind of curvature we've got. And we can begin to understand these relationships between the existing lines and the line that we've got. So we manipulate this to try and get a smoother curvature looking our curvature cone graph to see what we've got.

One other option you've got here is to choose Apply Intention. And if we choose Apply Intention and we bring out this little dialogue, we can use to adjust the degree of tension in that spline and smooth it off a little bit.

But OK. So interpolation splines are what we've always had in Inventor. They can be kind of tricky to work with. I'd recommend that you have as little or fewer fit points as possible to give you the nicest curve. But we do have a relevant ability of newcomer, the control vertex spline, which I also have to show you.

This time when we create points the curve doesn't go through the points we created. Each of these points is known as a CV or control vertex. And our curve is always going to be tangent to the line that comes off it. So by moving the point, we can adjust the degree of curvature, which is a little bit easier to deal with. We can add additional points, and again, just by right click to use this time instead of vertex.

And what you'll notice is when I click to insert a vertex, it's basically dividing that. It's subdividing each of those lines. OK. So those lines are called holes. So you have one CV and two holes to adjust the degree of curvature in this CV spline.

And if we click, we now have two CVs and three holes. If we were to add another one, it will subdivide again. And that means you got more points to adjust the acceleration of that curve in different places. So that's way simpler. I want to show you a couple of slight more practical example about how you might use that.

So I've dropped in here a sketch. So this is something we're using as reference to begin our surface model. So which spine we use in which case? Well, one of the nice things about an interpolation spline is an interpolation spline will create a closed loop. So if I work my way around this sketch using it as reference, when I hover over the closing point-- I don't know if you can see that there-- as I hover over the closing point, it creates a closed loop.

I'll hollow out that, see if you can see it. So we've got a completely closed loop of geometry. So interpolation spines do that really well. And that will maintain a G2 curvature. That will maintain a G2 curvature through each of those points.

Now, where I suggest you use a CV spline would be working on the outside of this shape. So you can have as many fit points in as you like, use those fit points to adjust until you get the kind of curve you're looking for. And then you will need to add additional curves for something like this.

And what we'll then do is apply our curvature continuity. So I'm using a G2 constraint to apply continuity. And then if I select both of these curves, right click, and show curvature, we can see that's actually pretty good curvature. I'm just going to go to select on the line again and choose Setup Curvature Display.

And that brings up a little dialog that allows us to adjust the height, just to help us see what's going on. As you can see, as I've adjusted the curvature here, it adjusted the curvature to the next one. So what we're looking for is really good tangency here. And that shows we've got the same degree of acceleration going in across this curve and across this curve.

So that's 2D, CV, and interpolation splines. I'm now going to jump in and talk about 3D splines. So in this example, I've created two sketches, the 2D sketches on different planes. But what I would like to do is create a blend that goes between the two. And I'll do that with the 3D spline.

So we start with a 3D sketch up here. Choose 3D Sketch. And I'm just going to create a control vertex spline between this point. I'm going to add [INAUDIBLE] between this point and this point. Choose Create.

OK? Now, in order to get that to be curvature continuous, I'm adding git points in there. So I'm going to choose Insert Vertex and just add some vertices in. Clicking it each time is subdividing. I'm going to add in three vertices. Now, although Inventor is automatically projected through this point for me and this point for me, in order to apply curvature continuity to this line and this line. I'll need to bring them into this 3D sketch. I'm going to use that as a tool called Include Geometry.

So in 2D we would have Project Geometry. But in 2D it's called Include. So our choose include this line, include this line, and it projects them into my 3D sketch. Now I can use the same continuity tool. So it's the curvature continuity constraint between this line and this line this line and this line. And that's given me the best blend I can get between those two curves.

But once again, if I want to control that a bit more I can turn on Display Curvature. And I'll display the curvature for those two curves as well. And you see I've got quite a good acceleration going from this curve to this one. This one's maybe a bit sharp. So then you could begin to use these CV points to adjust that curvature. See if you can get a slightly better result.

So we can use 3D splines to build these theoretical sharp edges. But typically-- just wanted to show you one more thing here, actually. So again, I just wanted to show you an example of how you might use an interpolation spine, again, for using a closed surface. So if I create a new 3D sketch here, once again, I've got some geometry underneath. This is 2D geometry sketched on two separate planes.

So this time I'm going to use my interpolation spline. And I'll start at one point, come down to the next, back up, back down, then I hover over that last point. Again, you can see it creates a closed loop with G2 curvature continuity built in. So that gives me my Pringle, which we could then use. We could then create a patch, then thicken it, and that would give us our surface model.

Here's a thing. Tell me how well that shows up in the projector. You can kind of see when you have a surface in a solid overlaid on top of each other.

You can see the isoparms there. OK? So along the Inventor is creating real geometry in the background. It actually uses the mesh, that mesh that it uses in the background to create the visuals on the screen. So you can kind of see those isoparms as yo go through.

OK. OK. So we can use 3D splines. But typically it can be quite hard to define a 3D spine in the middle of all that space. So typically, we would use 2D sketches. We want to map them onto a 3D surface. And again, there is some more tools in the 3D sketch environment. I want to just walk you through so we know what they are to do.

So if I'm going to project these curves down onto the surface, once again, I'm going to start with a 3D sketch. We're going to be looking at these tools here, projectiles. So the first one I'm going to choose is projector surface. I'm just going to choose the curves I want to project. I'll choose the face first, then choose the curves that I want to project.

And finally, it's asking me for direction. By default it's just pick the ends of that axis in my model. But I'm going to choose this axis because I want it to be tangent to the curve underneath, make sure I've picked that curve. Choose Apply. So you can see how it's projected onto that surface in that direction, using that direction as a vector.

AUDIENCE: [INAUDIBLE]

PAUL MUNFORD: I have to find that vector by placing a sketch point in the curve that I used to create that surface, and then using sketch point and the face of the surface itself to create the vector. So the question was then, do you have to create that vector yourself or can you use the normal direction of the surface? Actually, I'll show you the next tool It might help.

So this time we're going to look at the projector closest point, which I guess would be the normal. So once again, choose the face, choose the curves we want to project. This time there is no direction option. Inventors going to work out for us. Choose Apply. Let me just reset this so we can see this a bit better.

Now this time it's projected this curve to the closest point, projected this 2D sketch to the closest point you can find on the curved surface. So if I create a couple of axis it might help us just to see that a bit better. Create and axis here. Create an axis here.

So can you see that? Can you say it's just picked the closest point on that curve? So that means it has distorted our 2D sketch quite a bit. So there's one more option we can look at. Double click back into the Sketch Tool Editor.

The final option is the Wrap To Surface, so same sequence. Choose the surface, choose the curves, choose Apply. So it's projected that curve on the surface. But this time if I take a measurement here, I can see that this line is 25 millimeters. And if I measure the same line down here making sure I get the line and not the radius, you see that's also 25 millimeters.

So depending on which Project Curve Tool we choose would depend whether we preserve that geometry or not. OK? So by Wrap to Surface, we get exactly the same shape. It's just projected onto that surface.

So these tools are really useful for be able to build up sketches and have a little bit more control rather than using a 3D spline and kind of having to pick points in space and guess.

AUDIENCE: [INAUDIBLE]

PAUL MUNFORD: In the last case, that's a good question. It is going down. But you can adjust the position down here by adjusting the position in this one. So I guess you'd move that around to get where you need to be.

AUDIENCE: [INAUDIBLE]

PAUL MUNFORD: The question is which direction is the last one going? And it looks like it's going to the z of that one. OK. The last one I want to show you the Intersection Curve Tool. So this is an extremely useful tool. So once again, I've got two 2D sketches. But what I really want, I really want the combination of both. And I don't have to project surfaces to create that.

So once again, I'm going to start a new 3D sketch. I'm going to use this tool here, Intersection Curve. So I use Intersection Curve, choose one geometry, choose the other geometry, choose OK, and it gives me the 3D equivalent of them both, this kind of mapping one curve onto the other curve.

So that's an extremely useful tool, being able to create your 3D curve for your theoretical sharp edge. OK. Any other questions about 3D curves?

OK. So surface analysis, so once we created some surfaces-- so we've created our 2D curves. We projected surface geometry off them. We want to see that that seam in 3D has good curvature continuity. How do we tell?

Well, there are some tools inside Inventor we can use for analyzing curvature continuity. Now, I'm only going to show you the two main ones that I think you'll use most just because we're a little bit limited on time. Let's just shut some of these down that we're finished with. So the first thing I recommend-- this is something I like to do when I'm doing surface modeling-- is I light to use this silver appearance.

So it's up here under Appearances, Silver. And the reason I like doing that is because you can actually see pretty well as you work whether you've got any issues with curvature continuity. As you're spinning your model around, you can kind of see where you've got nice, sharp edges and where you got good blends.

But if you did want to do something a little bit more precise, you'll find in the Inspect tab you'll find your analysis tools here. So we're going to look at Zebra Analysis and Curvature Analysis. Draft Analysis is particularly useful if you're doing plastics, allows you to detect when you've got any undercuts. Surface Analysis is another way of looking at the curvature continuity. And Section Analysis is particularly good, again, if you're doing plastic parts to detect whether you've got any problems with thin walls anywhere, making sure you've got consistent wall thickness.

But for today, I'm just going to to show you the first two. So Zebra Analysis, when we pick that, it's going to give us some options. But I'm just going to say, OK. And what that does is project these black and white stripes all over our model. And what that allows us to do is to look at the curvature continuity across this model and see if we have any issues.

So we can see if we just shift to make sure I'm on Slate Faces and Edges. This is basically two main patches. I've got the primary patch here, which I've then trimmed back and add a second repatch in.

And then at this point I've asked for curvature continuity. And as I look across here, there's a little bit of a break there. But actually, it's pretty good. We can see how smooth these type of stripes are cross this joint, across this seam. Right here, where I was looking for a style increase, I can see there's definitely a break there.

So it's a visual tool, the zebra stripes are a visual tool if you inspect your model and see whether you've got any kind of issues there. Just a little hint, it's not too obvious. If you right click here, you can turn off the visibility analysis and turn it back on again.

The other option one to show is the curvature. So the Curvature Tool is right here. So this is the 3D equivalent of that 2D curvature tool we looked at with our splines. So once again, we would choose a face or a couple of faces we want to work with. I'll just pick the defaults and choose OK.

So this is going to project onto their curvature cones. And the distance apart they all depends which option which chose. That allows us to see the degree of acceleration we've got going across our model.

So in this circular feature on the top, you can see the acceleration is pretty much the same the whole way around that curve because it's a circle. So acceleration is the same. It's a constant radius. We can see down the front here the acceleration changes. We've got more curvature at side. It flattens off across the top, and then we have nice curvature again.

We've got good curvature in the seams. That's nice. We do have a bit of a wobble in the front. So you can see here that's maybe not as smooth as we could get it. But it rises right down the front there. I'm cool with that.

So there's a couple of tools that you can use to inspect your surfaces after you've created them. So you can kind of analyze whether it's as smooth as you would like it to be. It can be quite deceiving when you're looking at something on a computer model. It can look pretty smooth. If you try to 3-D print it, you might find it's not as smooth as you thought.

OK. So I'm moving on. What I would like to do next, what I've called surfacing gotchas. So there are some slightly weird things that you might need to deal with.

Actually, they're not weird. Inventor does it's geometry in a different way. If you don't understand it, it can look weird. So I wanted to give you a few hints and tips about how you might handle some of these issues.

So the first one I want to look at is high curvature. So we can say that this line here, this straight line we could say has low curvature. Or you could even say it's got no curvature. Unless your math geek, and it's probably got infinite curvature. That's not the way we're looking at it.

This line here definitely has low curvature. OK? So this one here is definitely high curvature. So where that could give is an issue is if we try to do a sweep around that curve. So I'll just show this. I'm going to sweep.

I'll choose the Surface option. I'll choose my profile. I'll choose my path. I'll choose OK, and it follows. Now, how many people know what happens if I click on the red text?

Cool. Here's a tip. It shows you a preview. Who knew that was there? I didn't know that was there. Nobody ever showed me that when I started learning Inventor.

Now, if you try and use your mouse, you can't navigate this. But if you're using a 3D connection control like I am, you can keep working on the model so you can see. The reason that hasn't built is because that curve is self-intersecting because of the high curvature. So now we know that's the issue. We can work around it.

And the work around here was to do it as a loft instead. So I had to replicate that 3D sketch on the other side and then do a loft from that edge. So there's a loft from this curve to this curve using the previous surfaces [INAUDIBLE].

So we do them with high curvature, you may need to think outside the box a bit and do something which is maybe not the most intuitive option. But that little tip there about clicking on the red text is a great diagnosis tool to help you realize what the issue is.

OK. So next one I want to talk about its near tangency. So in each of these surfaces I've created two surfaces, which are then joined together. And we can see here these two surfaces, it's pretty clear these are tangent where they join on this seam. And it's pretty clear here these are not tangent.

So this would be a G2. This would be a G1. So you've got this sharp seam where they join. This one here, it's a little bit tricky to see whether that's tangent or not. So in order to try and find that out-- so I did some curvature analysis on this. And I can see here that these two curves have got G3 curvature continuity.

So the curvature cones are telling me that where these two join on the seam, the curvature cones are the same length. So we have the same curve. And they're nice and tangent across the top as well as the curves themselves being tangent. So the curvature cones tell me I've got good curvature there.

We can see here on the one that's not tangent, we can see that although the curvature cones are the same length-- so we've got the same curvature-- they're not actually touching so we can see that we don't have that curvature continuity there. Now, we can also see on this one, now that we've done the curvature analysis, we can see that we don't have tangency because these two lines are not projected in the same direction.

But there is a slightly easier way to detecting near tangency. And that's just by selecting on the seam. So if I select on this seam, nothing. If I select on this seam, Inventor says, OK. What do you want to do? Do you want to do a fillet or do you want to do a chamfer?

If I select on this one, it offers me the same options. Do I want a fillet? Do I want a chamfer? So I know that that's near tangent.

OK. So if you ever get some slightly weird things going on in your model, and you think you've got good coach continuity, when you try and do your analysis, it doesn't look so great, maybe just select on that and see whether you've actually got tangency there or not. OK. Moving on to sliver faces.

So a sliver face, I'm going to quickly go into Shaded With Edges View. So sliver faces are typically more of an issue when you're dealing with imported geometry. So if you bring in geometry that's in a neutral file format or geometry from another CAD system that comes in as a surface, sometimes you have this little issue with sliver faces.

So if I zoom right in here-- so I've actually built this sliver face. And obviously, I recommend if you're building it yourself, just don't build sliver faces in. But I've had to build it to show you.