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Using the "shelling" technique to create wall thickness

From: Rhino 4 Essential Training

Video: Using the "shelling" technique to create wall thickness

In this video, we'll focus on creating wall thicknesses, which is also called shelling. Whether you're in prototyping or manufacturing, a big concern is maintaining a uniform wall thickness. But up until this point, we've focused all of our efforts on design, form, proportion, and generally making something cool, but now it's time to make it real. This process of shelling can get quite tricky. There can be as many shelling strategies as there are designers and designs. However, I've picked the shoe as a representative sample, so we can review a few common strategies.

Using the "shelling" technique to create wall thickness

In this video, we'll focus on creating wall thicknesses, which is also called shelling. Whether you're in prototyping or manufacturing, a big concern is maintaining a uniform wall thickness. But up until this point, we've focused all of our efforts on design, form, proportion, and generally making something cool, but now it's time to make it real. This process of shelling can get quite tricky. There can be as many shelling strategies as there are designers and designs. However, I've picked the shoe as a representative sample, so we can review a few common strategies.

Now notice that I've made an additional copy here. That's always a good idea when exploring a new direction. So, I'm going to work on that and leave these alone, just in case something goes wrong. I have the originals as backup copies. Turn off the robot layer. I'm going to zoom in here on the shoe. Now we'll notice that if we flip it over, it's all joined together. It also has no wall thickness. We can identify that by this has a single surface.

It's defining a perimeter. It's also open on the bottom, another major problem. It's currently joined. Let's go ahead and explode all of those pieces, so we can work on them more easily. Tip number one here. I would leave the bottom edge open until the very last. Tip number two is we're going to work on the outside and inside separately, because it can get quite confusing. Tip number three is we're going to do some Offset Surface commands to get those wall thicknesses. I'm going to start with this primary curved surface here.

So, I'm going to Surface > Offset Surface. Now these surface normals are pointing in the wrong direction. I'm going to offset to the interior, so I'm just going to click to flip them inwards. You have an opportunity to change the dimension. I just so happen to want to offset at one, so I'm going to leave the default, and I'm going to right-click to accept. So, we've made the first interior surface there. Let's get the wall thicknesses on the two ends. We'll notice that these are perfectly flat.

So, we can do the Offset command, or we can just copy them and move them. It all depends on the model. I'll try it both ways. Let's go to Surface > Offset Surface. I'm going to go in, looks like the unit is still set to 1. So, I'm going to right-click and we'll look inside there. It worked as expected. Now we'll just do the copy-paste on this edge. Ctrl+C to copy, Ctrl+V to paste. I'll just use my Nudge to move it in one unit, and I'll verify all this one more time.

So, here are the roughed out interior walls. We're not going to worry about that perimeter edge. We can do that at the very last. Now I mentioned we're going to break this apart at least visually, so we're only going to work on the outside or the inside one at a time. So, right now, I'm going to pick the outside surfaces and we're just going to hide them. So, you've got the inside there, so I'm going to use Ctrl to deselect and then Shift to add the top.

Hide command is this light bulb icon here, or you can use Ctrl+H and get rid of it just for a little while. Any longer than that, I typically would move those entities to another layer and turn it off. So, plan here is to trim these to each other. You're probably noticing well, how to trim them to each other? They don't intersect. So, we're going to go ahead and just scale these up a bit. It's not going to be critical as long as this face maintains the same position and orientation. We can scale it up and down. Then the trimming will be that much easier. We'll go to the Scale tool. Select the face.

I'm going to snap here to the Midpoint, so that is an edge even though there is no curve there, and just start and scale it out. Doesn't matter. We just want to make sure we go well past. The same thing on the other side, right- click to repeat, Midpoint, snap on the end, and make sure it's really easy to stop short, no charge for extra scaling, make it bigger than needed.

Another item here you're probably noticing is, well, how do I trim these to each other? There is an exact overlap here. So, what we're going to do is we're going to slice the bottom, so that we have a uniform bottom edge. That is the same and then the trimming will work. So, I'm going to switch over to the Front viewport, and you can see right off the bat, by virtue of those offsets, we've come out at 90 degrees and things kind of undulate up and down. So, this is another one of my tips. Whenever you have a surface that's getting a little complicated, always make it bigger than needed.

Then feel free to just trim it back, and then you have to maintain a perfectly clean edge. So, I'm going to just draw a quick straight line here. Hold down the Ortho or Shift key, make it la ot bigger, and that's probably too much trimming. So, I'm going to scoot that down with a couple of Nudges. That should do the trick. In most situations, a curve can trim a surface if both are fairly clean. Otherwise the backup plan would be to take that curve and extrude it straight and then trim with a plane, but let's give it a shot.

So, I'm going to use Trim command here. Cutting objects is the curve, accept, and let's see if we can get lucky. I'm going to trim some of these surfaces. First one worked. Here's the back plane and here is the shell. That's curved. Picked the wrong side. Ctrl+Z to undo. This is where it gets little tricky. You might want to zoom in, make sure you're picking the right part. There, got it. I've another one over here as well. The purpose of that is that they now share a bottom edge, and they can be trimmed to each other.

I'm going to show you a technique. Instead of just trimming them apart, sometimes it's a good idea to do a Split. You can verify that both shapes will trim to each other first, instead of trimming one and having the second one fail. It's a great way to have the built-in backup plan. So, objects to split, I'm going to pick a curved shell, Enter and then use these two as the cutting objects. So, I just want to verify that those broke off. If they didn't, I could use other parts.

So, that's the built-in backup plan. So, they worked. Let's split again. I'm going to split this face, Enter. Now I can pick either side if there is any problem or both sides. I'll just pick this larger side, Enter, looks like that worked. Let's repeat it for over here, cutting objects, shell. Okay. Once the Split Split technique has worked, next up is the stage called just throw away the garbage, pick the extra pieces we don't need.

Don't forget, we're still working on the inside here. That's the reason I turned the outside off. It would be very confusing if everything was upside down or inside out. Let's unhide the exterior. There it is. Let's take a look at how things are coming along here. So, we have a nice clean interior shell there. We do have to close off that wall thickness. Let's flip over to the Front view here, and let's switch viewports. Notice that it is longer and extended beyond the inside shell.

So, that's why we'll use this to trim one more time. So, hopefully, everything will trim out. I'm going to zoom in just to avoid any problems. They should now share a common flat bottom. It looks like we missed one edge. We'll go back and do that - this happens a lot - because we're seeing them straight on. Easy to miss. Back to Perspective, and this is why I like working in the Perspective viewport as much as possible. It's an opportunity to constantly inspect the surface and catch mistakes as they crop up. So, that looks pretty clean.

So, all we have to do now is cap this. Unfortunately, we can't use the Cap Solid command, because these two surfaces are no longer connected. They're completely separate. They don't touch anywhere. However, we can join all the pieces together pretty easily. So, I'm just going to select all these objects. I'm going to hit Ctrl+J for Join. Let's take a look. Inside shell all joined, outside all joined. So, now we're going to use this cutter to create a surface, and that will be used to cap those.

Again, we can't use the Solid Cap command because they're not touching anywhere. We'll just do a simple Surface > Extrude. This happens a lot too- especially when we're working with Perspective, it goes the wrong way. That's because it typically goes perpendicular to the construction plane unless the curve is rotated. Not a problem. We just say new direction by clicking this option and all it's asking here is just for two points. I'm going to click there. Holding down Shift, pick the second point in the direction we want to create the Extrude, selected the BothSides, Yes, and make it way bigger than needed.

Now we have a flat cap just about ready to split or trim. Let's start the Split command. Objects to split will be this flat plane, Enter, and we'll select the two surfaces. Don't forget, you have to get the interior. The outside will light up first. There is the inside, hit Enter. If everything is going as planned, it'll tell you one surface was split into three pieces. That's actually a good visual check. Let me zoom over here and notice we have an outside and inside and that lip.

That's the three pieces. So, again, we can throw away the garbage. It looks good. We still have to join them. So, here is the new edge inside plus outside. I'm doing Shift, add, Ctrl+J or Join, cross your fingers, and this is the-- hallelujah! Command line prompt. X number of surfaces or polysurfaces joined into one closed polysurface. So, that would be ready to prototype.

It's clean and it's closed. So, there you have at least one way to shell a robot shoe. These few tips will hopefully get most of your shelling needs streamlined, but it's also worth noting that some smaller thin parts may not need shelling as they sometimes can be built solid. With that in mind, we'll tackle the arm next and prepare it for prototyping exporting.

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This video is part of

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Rhino 4 Essential Training

67 video lessons · 16847 viewers

Dave Schultze
Author

 
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  1. 4m 13s
    1. Welcome
      1m 1s
    2. Using the exercise files
      28s
    3. Recommended hardware
      2m 44s
  2. 19m 8s
    1. Understanding the three types of entities: curves, surfaces, and solids
      5m 51s
    2. Comparing Bezier curves, B-splines, and NURBS objects
      3m 35s
    3. Comparing isocurve surfaces and mesh surfaces
      4m 50s
    4. Setting measurement units and tolerance
      4m 52s
  3. 18m 16s
    1. Introducing the viewport
      3m 20s
    2. Using construction planes to anchor model design
      5m 27s
    3. Changing the way a model is viewed using shading modes
      3m 11s
    4. Navigating the viewport with pan, zoom, rotate, and reset controls
      3m 24s
    5. Exploring help options
      2m 54s
  4. 29m 48s
    1. Understanding Rhino's command philosophy
      3m 10s
    2. Using toolbars and docking buttons to a toolbar
      3m 33s
    3. Navigating the geometry menus using a "department store" analogy
      3m 35s
    4. Using the command line and status bar to get feedback
      4m 56s
    5. Modifying the nudge control and setting other preferences
      6m 54s
    6. Using the Properties window
      3m 1s
    7. Opening and saving files
      4m 39s
  5. 14m 24s
    1. Creating basic objects: curves, surfaces, and solids
      4m 22s
    2. Performing basic transformations
      3m 14s
    3. Selecting objects
      3m 37s
    4. Organizing a project using layers
      3m 11s
  6. 21m 18s
    1. Understanding lines and polylines
      4m 10s
    2. Building rectangles and polygons
      5m 12s
    3. Creating arcs, circles, and ellipses
      7m 8s
    4. Drawing freeform curves
      4m 48s
  7. 47m 36s
    1. Comparing different types of 3D surfaces
      7m 11s
    2. Extruding surfaces to create features in a model
      8m 58s
    3. Creating surfaces with lofts
      7m 49s
    4. Using Revolve and Rail Revolve to create surfaces
      7m 42s
    5. Using Sweep Rail to create a 3D claw
      7m 49s
    6. Creating complex surface shapes using Network Surface
      8m 7s
  8. 46m 48s
    1. Introducing solids
      5m 42s
    2. Making solids with primitives
      5m 41s
    3. Extruding curves to create solids without primitives
      8m 59s
    4. Creating unique shapes with the union, difference, and intersection Boolean operators
      6m 46s
    5. Troubleshooting solids and Booleans
      8m 53s
    6. Editing with the solid edit tools
      6m 20s
    7. Creating and transforming holes in solids
      4m 27s
  9. 27m 8s
    1. Understanding Rhino's modeling aids
      3m 59s
    2. Working with the Grid Snap modeling aid
      2m 22s
    3. Using the Ortho modeling aid
      3m 4s
    4. Using the Planar modeling aid
      2m 4s
    5. Incorporating the Osnap modeling aid into your workflow
      6m 7s
    6. Understanding the Project and Smart Track modeling aids
      4m 42s
    7. Setting cursor constraints
      4m 50s
  10. 50m 14s
    1. Editing corners with Fillet and Chamfer
      7m 38s
    2. Trimming and splitting with curve Booleans
      5m 37s
    3. Moving and rotating objects with the Drag and Nudge tools
      7m 24s
    4. Copying and pasting objects
      4m 10s
    5. Understanding how Rhino uses Undo and Redo
      3m 42s
    6. Grouping objects
      3m 21s
    7. Scaling objects
      6m 40s
    8. Duplicating objects using the Mirror command
      6m 36s
    9. Making copies and structured sets using arrays
      5m 6s
  11. 20m 37s
    1. Using the Analysis toolbar to understand characteristics of a model
      6m 14s
    2. Defining degrees of curve and surfaces
      6m 6s
    3. Using Rebuild and Change Degree
      8m 17s
  12. 26m 21s
    1. Measuring and labeling values on a model using dimensioning
      5m 22s
    2. Creating screen captures for quick proofs
      5m 16s
    3. Creating 2D views of a 3D model
      6m 44s
    4. Rendering a project
      8m 59s
  13. 22m 5s
    1. Preparing a model for prototyping by confirming that all gaps are closed
      5m 17s
    2. Using the "shelling" technique to create wall thickness
      10m 54s
    3. Exporting to the STL format for 3D printing
      5m 54s
  14. 14s
    1. Goodbye
      14s

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