Rhino3d Video Tutorials Transcripts - To further support you as you learn and progress with Rhino we've transcribed each of our video tutorials.
Hi I’m Phil from Simply Rhino and in this video I’m going to continue with our engine cover model.
First I’m going to take a look at creating this scoop on the main engine surface.
There are two main considerations here. First we need to maintain a seamless continuity between the main surface and the lead in to the duct. Second, we need to control these edge blends so that they transition from a relatively straightforward edge blend condition and then run into the main engine cover surface. These are both fairly common problems in 3D modelling, even though the specific context might be different. Once we have the scoop completed, we’ll then take a look at mirroring the two halves of the engine cover and then creating the final centre blend. Finally, we’ll make sure that everything is ready to export into SOLIDWORKS.
This is the result we obtained from the modelling we covered in the last video exercise. Now to start to add the duct detail into this top surface, first of all I’m going to extract the top surface, the main top surface here and I’m going to hide the rest of the geometry. I then need to add some curves to describe the sharp boundary of the duct area. These can be either curves that you draw and then project onto the surface, or in this case they are actually created from isocurves. The advantage in this case of using isocurves to create the boundary shape of the duct, is that the shape that’s created will be very close to the overall shape of the surface.
So to create these curves, I went to curve, curve from object and extract isocurve and toggle to produce curves in the other direction. Then once I have these curves, I can trim them up with each other and join them. We need to make sure by just checking in object properties that the curves when they’re joined, produce a closed curve. Once we know that’s the case, we can then go ahead and split our main surface with this closed curve and I’m just going to hide the curve now.
Now of course, because these two surfaces are essentially derived from the same parent surface, then if we go to our analyse and surface and Zebra tools, then of course, the area that we’ve trimmed out will be completely curvature continuous with the surrounding area. And the idea here is that we’re going to leave the front edge of this surface as it is and adjust the rear edge of the surface to create the scoop and the fact that we don’t change the front of the surface means of course, that it’s going to be curvature continuous with our existing surface.
Now the first thing that we need to consider here is that if we look at the control points for our small trimmed surface, they actually describe the overall larger surface, because when you trim a surface you don’t actually change the control point structure. What we can do to make our control points here more manageable and relate more closely to our trimmed surface, is to select the surface and run a command from surface, surface edit tools, called shrink trimmed surface. What this command does is that it re-approximates a new surface that has the same shape in UNV. It has the same number of control points and the same degree in UNV. The idea being that now our control points are relative to our smaller surface, but when we analyse the curvature of this with our Zebra tools, we’ll see that our surface hasn’t changed in terms of its shape and so our two surfaces are still completely curvature continuous.
If we take a look at the control points on our newly shrunk surface, what we know is that these first three rows of control points need to remain exactly where they are in order for us to maintain the continuity at the leading edge of the scoop or duct. So it’s only these three rows of control points that we can move.
Now before we go on to really look in more detail at the shape of the scoop, let’s have a look at the principle behind this. So the principle is that we don’t move the first three rows of points, we leave those exactly where they are and the subsequent points we can move. Now a good way of moving these is to use the move UVN tool which is situated in the transform menu. What the move UVN tool does is move control points, either in the U direction, the V direction or the N direction (the normal direction) relative to a surface. Now normal means locally perpendicular. So each one of these control points will move locally perpendicular to the surface, so this is an ideal tool for either adding a recess or a protrusion to an existing surface. The value that we put into this box here, in to the scale box, is a real world value and if I move a slider from the mid-point to either end of the slider here, I’ll move the control points by 12mm in a normal direction to the surface.
So if I grab these three rows of points here, and move them, you can see that I can start to create a dip in the surface. And very quickly, just to show the principle, I’m now going to grab the last two rows of points and move those downwards and then finally the last row of points and move those downwards again. So you can see now I’ve started to create a surface which of course now changes from our original surface and starts to create the scoop.
Now because we haven’t moved these front three rows of control points, when we look at this tool with Zebra’s, you will see that we have perfect curvature continuity between our existing surface and our new surface at this leading edge and so the principle really is that we don’t need to worry about matching this surface to our existing surface because we know that our control points are already doing this for us.
Now the one downside here of this method, is that we don’t have very many control points to play with here and there’s a large area of this surface that we can’t move. So what we could really do with introducing here are more rows of control points so that we can put a little more shape in to our scoop and that we can have the scoop starting to change direction, a little closer to this leading edge.
So if I just undo my move UVN operations, and get back to where we were a few steps ago, I’m going to look now at introducing some control points into this surface. Now the way that we do this is important. If we just add control points into the surface we are going to change the shape of the surface which of course is then going to change our matching. Likewise, if we rebuild the surface. So what we really need to do here, is to insert knots into the surface which will add control points by implication. So I’m going to go to my edit tools, control points and insert knot. I’m going to pick this surface here and I’m going to add a knot line just behind this first three rows of points and then I’m going to add a knot line just behind the what is now the fourth row of control points. And this is the result that I’ll get now. I’ll get my three control points which are still controlling the matching, have now effectively moved much further forward. So now I can move all of these points and get more shape going on in the scoop.
So again, I’m going to do something similar here. I’m going to go to transform, move UVN, maybe adjust this distance slightly and I’m going to move all of these control points down. The nice thing about this tool is that being slider based, is that you know you can push this back and get back to your original position and I can then change the value here and it’s a nice tool to actually interact with.
So I’m gradually going to push this shape down. Now what I’ve decided to do here is I’m actually going to move these last three rows of control points together. So I introduce a kind of S-Shape into my duct surface here. And the idea about using move UVN here is that the surface that I’ve now created still has a lot in common with the top surface, so that this edge is going to be fairly common to this edge and the fall off as it goes from left to right here, is going to be fairly consistent with this surface. So again, let’s take a look at the continuity here. So that front edge looks okay. Let’s also take a look at this with an environment map. Okay, and that looks quite nice. So you can see that we’ve got a seamless transition here between our two surfaces.
So the Zebra stripes that we use here, really only give us an indication of whether we have curvature continuity across our two surfaces. So to check with more accuracy, we can either go to analyse, curve and turn on the curvature graph for both of these surfaces, or sometimes where we’ve got a simple proposition like just one single edge here, we can go to curve and curve from objects and we can extract an isocurve from both surfaces and make sure these isocurves are coincident. Then we can go to analyse and curve, and geometric continuity and we can test the continuity across those two curved ends. Here we will see that Rhino is reporting these are G2 which are curvature continuous and we could check this in a number of positions along this edge. So once again here, technically what’s doing this for us is that these five control points here, the middle one of which is a coincident point are required for a G2 curvature match. If we wanted to match beyond G2, then it’s the next pair of points that would be required to be involved in the match for a G3 match. But in this sort of situation here, G2 curvature and continuity is fine.
Let’s now take a look at making the side surfaces for the duct. First of all I’m just going to check my distance between this point and this point, which is 36mm and I’m going to have some fairly simple linear sides to the duct but I want to put a ten degree taper on all three sides of the duct.
So how I’m going to look at doing this, is first of all to draw a line. This line I’m going to make slightly longer than my depth of the duct. So let’s make this 50mm long and I’m going to put a point on the top of the line and then I’m going to rotate this about the minus ten degrees that we need here. This is drawn in top view and we’re working in our world top C-Plane which is also shared here by our perspective view. The idea now is I’m going to orientate this curve on to these three edges, doing this in three separate operations and to do this, I’m going to use transform, orient, perpendicular to curve.
So this is the object I want to orient and this is the base point and let’s start first of all with this rear edge and you can see I can orient this on to this edge and make sure the copy option in my command is turned on and I’ll snap this to one end of the rear edge. Okay, and then I’ll repeat this process for the sides. So transform, orient, perpendicular to curve, object to orient, base point and edge. It helps if you can look down the curve when you use this command, just to make sure that your ten degree angle in using this example is facing the correct way. So once more, transform, orient, perpendicular to curve, object to orient, enter, base point and then pick the orientation curve.
Here I need to flip the orientation in X to make this taper inwards and then snap to the end of the edge. Once we’ve achieved the orientation, we can then use a one rail sweep to create the various surfaces. So surface, sweep one rail, do the sides first. This is the rail and this is the cross-section curve. When I use this command, I can use the simple sweep option here to give me some simplified geometry and a cleaner result. Repeat the process over here, rail, cross-section, simple sweep and then do this for the rear.
So next we need to trim these surfaces with each other. So I’ll just remove these curves and to trim these surfaces, I’m going to generate an intersection curve between the surfaces in question to start off with. You’ll see that the surface edges don’t actually run into each other exactly here. So the process that I’m going to use here is something like this. I’m going to go to curve, curve from objects and intersection, generate an intersection between this side and our scoop surface. That gives me a nice intersection curve and then just to check that this curve is running all the way along both surfaces, I’m going to go to curve and extend curve, curve on surface. And then I can trim these portions here.
I can do the same on the other side, so curve, curve from object, intersection and then curve, extend curve, curve on surface and then I can trim and then finally this one here as well. Okay and then we should be able to trim these surfaces now with each other.
So I can select my curves, delete the curves, select everything and join everything together and then I want to check to see if all these edges are closed. So select the polysurface, go to my analysis tools, run show edges. Make sure that only naked edges are selected in here, use a nice bright colour and you can see that all of this is closed up nicely in here.
So we’ve now got our kind of sharp version of our scoop or duct. So now I can start to add in the blends. So first of all I’m going to put in two larger corner blends. So I’m going to go to solid, fillet edge and blend edge. I’m going to use a radius here of 50mm and I’m going to pick this edge and this edge and then enter to get into the preview and the rail type that I’m going to use here is distance between rails. So this takes a perpendicular measurement across these two edges here, and then I’m going to enter and let that build. Again, you can check this page with the environment map just to make sure everything looks okay and then now for the more difficult part.
So as previous, I’m going to use the solid blend edge tool for this top rail and this lower rail here and as in the previous video, the blend will build correctly up to the point where the edges of the blend run into each other and then they will cross into each other. That’s fine because it means that the rear part of this blend will build correctly and the difficult part we have for manual control over.
So let’s build our starting blends. So solid, fillet edge, blend edge. I’m going to choose a radius of 10mm here and I’m going to pick the entire top edge, and then the entire lower edge. Enter, and look at the preview we get here. You can see that the outer edges of these rails possibly are not too wrong here, but Rhino isn’t really able to trim up the interim part here, and this edge over on this side, again the outer edges are almost probably where they need to, but again, nothing is built in the middle here. But this is a fairly easy solution now for us to remedy manually, so I’ll Enter to build the blend, and what we have here is a series of surfaces that have not trimmed my sharp sided poly surface at all. And what I need to do first of all, is to split these surfaces about the point at which they intersect each other. So, I’m going to go to Surface, surface edit tools, and split at iso curve and I’m going to just make sure I find the correct point here, turn shrink on here and split this piece of the blend and then split the upper part of the blend again with shrink on at the coincident position. Now I’m not going to throw away the front of the blend because I may need those later on, so I’ll just hide these. And, I’m going to do a similar thing over the other side here. So surface, surface edit tools, split at iso curve, just zoom in, just make sure we drop right on that intersection, make sure we enable the shrink option and split, and then same with this surface, and then hide these front parts. OK, so, if I just extract these portions for a moment, we can then hide this part and let's just trim away the side surfaces now with these blend parts. So I’ll run Trim, I’ll type in CRV so I can only pick edges, and I’ll start to trim away these sides. Ok, so each time I’m picking the curve option here, and just carefully trimming away these surfaces. And then the final piece here, ok and then we can join these together, and we can check that these parts are joined together correctly here, that looks good, and then just take a quick look at these surfaces, make sure everything looks alright there, that looks fine. Ok, so now let’s show back in the rest of the poly surface that we need here. And let’s look at what we can do with this front. What we need to avoid with these fillets as they come towards this front edge, is running them to a point. It’s perfectly valid to have a fillet condition here to run into a point, but in this case the geometry is not going to look quite right for us, but more important than that, because we have essentially one or two three-sided surfaces that are going to converge to a point, that’s going to give us a big problem when we offset to give us our B-surface when we shell this out. It’s going to give us a condition that will fail, so we want to create here a condition that not only looks good, but is also going to have enough integrity to be able to shell later on.
Now, if we look at, for example, the one side of what Rhino actually built for us, you’ll see that there is a fair amount of consistency about these rails here. And, if we continued this edge, the front edge of the scoop here, along here, you can see that we can get two four-sided surfaces here that start with the two blend shapes, and then, blend into the main engine cover surface at the front. So, we can actually use most of these edges that Rhino has built for us here. So let’s just look at this side first of all. I’m going to just explode this surface so this part and this part are separate, and I’m going to extract and iso curve here from this main surface, and snap that to this leading edge. Remember we created this leading edge with an iso curve, so this is helpful to us now. Now let’s bring in the other surfaces here as well, and you’ll see we have a similar sort of situation here where the consistency of these outer edges of these fillets is actually quite good. So, I should now be able to run trim and again type in the curve filter so I can only select curves and edges, and I’m going to trim the scoop surface with those edge curves, and then I’m going to duplicate these two edge curves. Curve, curve from objects, duplicate edge, there. Ok, and now I’m going to hide these surface parts here, I won’t delete them just yet in case I need to backtrack at any stage. This here can be trimmed up like so, and here this edge is a little short so I’ll extend curve, curve on surface here, and then I can trim these parts up with each other. Now I should be able to trim this outer blend edge from my main surface. So this is a combination of curves and surface edges here. So I’m going to run, trim, use the curve filter and then pick these edges, and these front curves, ok and trim these out.
Having trimmed our top surface with the outer boundary curves, we can now join everything together and then select any remaining curves and delete those, and check using our edge analysis, that all our edges around here are joined up correctly, and also as we go along it’s worth checking with an environment map and also Zebras as we go to make sure we’re not storing up any problems. So, just want to look at the continuity here, need to zoom into these areas to see Zebra’s, and we may need to adjust meshes as well.
When we created the corner of the main surface in the previous video, we introduced a blend curve from this point here to a midway point on this edge. And we created two four-sided surfaces and then matched to each other. We can do something similar here and before I do that I need to make sure that this short edge here and this short edge here is split about its midpoint. This should have been the case from when we trimmed, but just to make sure that indeed the case we can go to Surface, and edge tools and split edge, we can pick this edge here and split it about the midpoint, re run the tool and do the same over here. Ok, now if we were to the adjustable blend curve, we can either blend curves or edges, but we can’t blend one of each, so because it would make more sense to use a curve for this position, what I’m actually going to do is to generate an iso curve here and here that snap to the split edge, So I’m going to go to Curve, curve from objects, extract iso curve and snap to the end here and the end there. So now we can look at creating the adjustable curve blend. So let’s go first of all from this curve here to the lower edge of this top rail here. So let’s go to my adjustable curve blend tool, pick this curve, and then this edge and we’ll blend between there.
Now, because of the way that the geometry is working here, we’re going to see a big difference in this curve between blending from this edge and this edge. So let’s repeat the adjustable curve blend, and blend this front curve to this edge. And here we’ll see that we generate two quite different looking curves, and probably what we want is somewhere that’s between these two curves. And there is a method here that we can use that will give us that result. So, I’m going to delete these two curves and I’m going to create a curve that’s an average of this edge here and this edge here. So to do that I’m going to go to Curve and tween curves, and I’m going to choose this edge and this edge, move my cursor to the left edge and click, and you’ll see that I can generate a curve now which is an average of those two edges. And if I go back to my adjustable curve blend here, we might see that this gives us a slightly better looking result. Now, we need to look at this curve carefully and make sure, for example, that this curve isn’t dipping below this scoop surface here. So, let’s just take a look in right view here and confirm that and that looks ok for the moment.
Now, with this process there may be an element of iteration, so we may need to redo this process a few times, but for now I’ll use the similar process on the second side so, tween curves, and then adjustable curve blend, and take a look at this curve as well and we’ll accept that, and then we can start to build some surfaces. As previous we’re going to start by using a sweep to rail here. So, rail, rail, cross-section, cross-section and I’m going to match curvature at point A. And I’m going to take a look at the result that we get here. So that looks OK with the environment map and let’s have a look at this with the Zebra’s, what we can see if we go in close to this front edge here is we’re slightly out of continuity there, and let’s have a look at this point here, and again, slightly out here.
So, before we start to get too worried about that little lack of continuity, one thing that will help the Zebra’s is actually joining these two surfaces together. So let’s do that and see what this front edge looks like now, and you’ll see that looks a lot better. So, for the moment I’m going to leave the surfaces as they are, we should just actually check, I guess, that these are actually joined up properly, Ok that’s fine, and let’s build in our other surface here. And let’s again use a sweep to rail. So, edge and edge as the two rails, and then these two edges as the two cross-sections. Match, curvature across both, let’s join them, check first of all that they join up, that’s ok, and now let’s have a look at the analysis. Ok, so shape wise that doesn’t look too bad there, and let’s take a look at the Zebra’s, just look right across that front edge, that looks ok. So, let’s take a look at doing something similar on the other side. So, surface, sweep two rails, first rail, second rail, cross-section, cross-section, and let’s match for curvature on that top edge. Take a look at this shape that we get here, ok, that looks ok, and take a look at the front edge with the Zebra’s, just pull right into that edge, it’s not too bad, and let’s build another sweep in here. I want the edge here and not the curve, edge here, edge and edge, match for curvature, cross both of the rails, join, check the join and repeat the work with the environment map. Ok, so we should see that we should get a pretty good result here. Now, in some circumstances you may find that as we get towards the front here, that this edge becomes slightly problematic. So you might need to consider building a four-sided surface here, matching to three sides, splitting the edge of that surface and then, in other words, giving a little more room where this is one single surface, might help the shape of the front of the blend in some instances. So, once we have achieved this we can show in our other parts of the geometry, and join back together. Once we’ve joined the surfaces together, we just want to make sure that our result is a closed polysurface, and also we can just run the environment map again just to make sure that we’re happy with the various blends that we’ve created.
Now it’s time to look at adding any additional detail, and then to mirror the other half of the engine cover. So I’m going to extract this centre planar surface here, and delete that, and then just run the mirror tool. Here, the copy option, fairly obviously is on, and I’m just going to hit the y axis option here to mirror about a line of symmetry. I can then join the two halves together, and take a look at the result again with an environment map. Ok, so, for this centre blend here, I could use the solid blend edge tool, but there’s possibly an easier way to do this. I just want to check the distance across the perpendicular here, 19.999 so it looks as though I used a 20mm blend across this edge. And I’m going to go for something similar across the middle here. Actually, I’ll probably use something slightly sharper across the middle, and let’s look at a pretty easy way that we can do this. Going to take a line here, with the both sides option, start the line at Zero and pull the line along the centre of our engine cover here. And then I’m going to offset this curve with the both sides option on, by a distance of 8mm. so I’ll have a 16mm overall blend across the centre. And then I’m going to pick the two outside lines here and just trim away my engine cover. So, we’ve not got a gap here between the two halves of our engine cover and I’m going to use the blend surface tool to create a blend across these two front surfaces, and across the two top surfaces, and then this area here I’m going to blend separately, because I really need to control the shape of this blend correctly across here. And then, for the underside and the back, these are just fairly simple plainer surfaces.
Now, I want to make sure that I’ve got enough shape to the blend here. So, I don’t want this blend to be too flat. So, I’m going to run the blend surface tool here, first of all across this edge here, and I’m going to lock the sliders, I’m just going to push up the blend a bit here. Just make a note of this blend factor that I’m using here, and let’s just have a look at this with the environment map. I want to make sure that I can see a reasonably sharp blend across this centre, ok, that looks ok. And then I’m going to use a blend with the same factor on the front edge. So once again, lock the sliders, and use the same factor here, and then also take a look at this, ok, that looks ok. Now, you can see that this blend here is built slightly short and as a result, what I’m going to do is extend all of the edges of the blends just slightly here and then I’m going to trim them off. So let’s extend this by a couple of Millimetres, and this one, this one and this back edge here. First of all let’s do the easy parts here, let’s just trim with a line this piece of blend here, and do the same at the front. OK, and then to get the shape of this little nose piece right here, I’m just going to use a technique that we’ve used before in this exercise, I’m going to use the adjustable curve blend, blend across here, with the curvature continue as blend, and do the same here, and then I’m going to take this and pull it back on to the blend surface and then trim away the blend with it, and then likewise do the same here.
Ok, if we blended this all in one go, so we blended this, this and this part here, then we wouldn’t get this curved shape going across here, I think this is going to be important to explain the shape here when we see the final result. So now we need to look at just creating the surface that’s going to fill in this little nose area here. Now, I could use a two rail sweep here, but the issue will be in actually getting this edge and this edge, which are the cross-section edges, to actually join into a watertight condition. So I’m going to look at using a network surface here.
Now, the disadvantage of the network surface, is that it’s going to be slightly complex. But because my geometry is reasonably good here, and my boundary shapes all have a lot of similarity to each other then I think the result should be ok here. So, going to use curve network, pick the four boundary curves or edges, match for curvature on each edge and the important issue here is to make sure that this value here and the tolerance is the same as your absolute modelling tolerance that you’re working to. So, here we’re using the default small objects millimetres tolerance of .001 of a millimetre, and that’s the value I need to set in here. If I slacken this value off then my surface will be less complicated, but there’s less chances that my edges will actually join into a watertight condition.
So, I’ll preview that surface, I’ll ok this, I’ll join this together, and now we can take a look at what this looks like. Ok, so, that looks ok, and let’s take a look at this with the Zebra stripes. Let’s firstly take a look, make sure that this is joined up into a watertight condition. Yep, that’s ok, and let’s take a look at the Zebra’s across the edges here. OK, so that’s pretty good, ok I can’t see any disruption along these edges here. So, all we need to do now is to create our plainer surfaces to close off the volume. So, just draw a little line across here, and then use surface from planar curves, here join this together and I can just cap to finish off the lower part. Ok, so, we’ve got a closed polysurface now, so, just a few things now that we need to do to get the geometry ready for SOLIDWORKS. First thing is that, any co-planar surfaces like this are possible issues for solid work, so we can clean these up very easily. Pick the geometry, go to our solid tools, and right click on this tool here, and this merge all co-planar faces. And any coplanar faces here will be merged. Ok, so you can see that this face now is once face, as is this one here. The other tool that I need to run here is, Shrink trimmed surface. And I can run this on a poly surface here and it will shrink the individual surfaces. So, surface, surface edit tools, and shrink trimmed surface. Ok, and here it’s going to shrink 75 surfaces and 44 are already shrunk. The solid modellers will work much better with trimmed surfaces, the disadvantage of shrinking is that if you need to un-trim and re-work any of the blends, then you may have reduced the size of your base untrimmed surface by too much to do this. So you would generally do this on a copy of the geometry.
So, one last thing that we should do now is to pick our geometry and run check, just to make sure our poly surface doesn’t contain any bad surfaces, and, that’s all fine, and so we’re now pretty much ready to move downstream in this case to SOLIDWORKS. So I hope you found this video useful and thanks for watching.