Need a little modeling help!

Firstly, I am using Rhino on OSX but I think this is a generic question. I don’t think I quite understand the difference between an extrusion created from a surface and a solid. They both show as “polysurface” in the Details pane. I basically want to union them to make a new solid. I’ve attached a simple example of a simple cylinder that was extruded from a planar curve and around its perimeter is a “tire” (for lack of a better description) that was created by drawn a closed curve and then sweeping 1 rail to “wrap” it around the cylinder. Now I want to join the two and have no clue after trying everything I can think of. I’ve attached the source file and would appreciate any insight.

MichaelFlyingDisk.3dm (408.0 KB)

First remove the surfaces that are shared by the two volumes (ExtractSrf), then join the two polysurfaces (Join).
FlyingDisk2.3dm (345.9 KB)

Thanks Marc, I have no idea how to do that! This might be part of the problem. I’ve only been using Rhino for a few months and used a pretty low end CAD app before that.

Ok, I got it, thank you for point the direction!

Now the basic question is, how would I have known to do that?

Rhino has a very hard time with coplanar and duplicate surfaces for boolean unioning and joining because the computer has no idea how to “unfold” the surface (oops… I mean, “unroll” in Rhinospeak)

The concept at work here—especially for creating watertight solids for 3D printing— is that every surface has a direction, and these all have to point in the same direction for optimal results (and proper unfolding)

Rhino has a VERY nifty feature that only a handful of (OK, only two other) programs I know of have—which is to color the backfaces. Why McNeel does not showcase this extremely powerful (and almost totally unique) feature, and turn on single color backfaces as the default remains a complete mystery. I used Rhino for two years before someone told me about this feature that I rely on like oxygen in my work. When I mention this to most people, their reaction is ZZZOOOOMMMMGGGGG!!!

Here’s how it works: When backfaces are on, and you have duplicate surfaces, you will often get a “moire” pattern, for lack of a better word. Like this, from your problem file:

When you get this sort of moire, you need to delete at least one of the surfaces. In your case, both actually need to be deleted if you’re after a 3D printable watertight solid using the outer “tire”. With both inner surfaces gone, you can then add the curved outer part and join it all up. Like so:

See how all the grey is on the outside and the orange is on the inside? Think of it as a candy-coated chocolate and you get the idea. When you bite into it, you can see the chocolate on the inside, and the candy coating on the outside.

Here’s how to turn on Backface coloring (which, is buried far, far deeper than it should be, methinks):
Menu > Rhinoceros > Preferences > Display Modes > Under Standard, pick all views that you want. In my case, I use Shaded and Ghosted display modes with back face coloring.

Then do the following separately for each display mode you’ve want to use this feature in:

On Right > General > Shading Settings > Backface Settings > Choose “single color for all backfaces” > Single object color > pick your favorite. (I like orange, can’t you tell?)

Completely obvious, right? :stuck_out_tongue_winking_eye:

To check for watertightness, select all objects, Menu > Analyze > Edge Tools > Show Edges. Select Naked Edges. Look at the prompt. It should say “no naked edges, no non-manifold edges” (And this is also a killer feature!)


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Dave, this is totally awesome thank you! I’ve enabled backface coloring and it does indeed rock!

Thanks for the analyze edge tip too! In this case, I get 3 backed edges. What is the strategy for removing those?

Ok, I couldn’t figure out HOW to eliminate the naked edges but I did realize that I could redraw the inner disk and eliminate them now that I know how to remove surfaces and join. I’m beginning to make some sense of it I think!



Glad this is starting to make sense!

As for trying to heal naked edges, you’ll find that with existing geometry, using Menu > Curve > Curve From Objects > Duplicate Edge/Border, will be very helpful to extract new geometry to turn into a surface that mates with these surfaces.

Keep at it!


Thanks a lot Dave! I appreciate the help and pointers.

I think I just don’t / didn’t understand the concepts of edges, surfaces and solids. I’m starting to fill in those gaps. Are you aware of any good references on the basic Rhino concepts (without spending an arm and leg for training, which I typically don’t enjoy taking)?

FYI, here’s the kind of stuff I do, I’m a reelsmith, maker of fly fishing reels:


Very nice progress on your model, Michael!

As for resources, I recommend, in Rhino, Menu > Help > Learn Rhino > Open Level 1 & 2 Training Manual. Written for WinRhino 4, it is largely transferable to MacRhino 5.

Very understandable. Few resources seem to directly address some of these concerns. Lessons are often learned the hard (and frustrating way). Incidentally, I’m currently writing a book for John Wiley & Sons (related to modeling for fabrication). Provided I keep on schedule, it’s planned be published this Fall. The content may help shed light on some of the fundamental concepts you’re encountering with regard to surface modeling.

If you’re interested in reviewing and providing feedback on material under development, shoot me an email: david at digifablab dot com. I’m in the process of lining up interested reviewers for the early chapters.

Keep at it, you’re doing a great job!


Thanks, I did start to go through those but got busy actually designing! I need to circle back around now and go through them to fill in the gaps.

I forgot to include this, the 3D reel that was printed from the design I posted. To the best of my knowledge, it is the first fully functioning, completely printed (no metal parts, fasteners, etc) fly reel:

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What material did you print it in?


The gold is Faberdashery’s (a UK company) Bling, Bling Gold PLA and the black is Ultimachine’s black PLA. The gold is spectacular in person, I am taking much better photos under studio lighting (another “hobby”) to try to do it justice. The black looks like licorice!

I’ve also printed these in ABS and Nylon. PLA is nice though so I can say it’s a renewable biopolymer and is biodegradable!