Joining a revolved surface and a extruded surface

I am having trouble with creating a smooth surface when joining a revolved and extruded surface. The surface does not seem to match up and there is a small gap when looking at it in rendered mode, even when toggling the mesh render settings to slow.

I have tried trimming the surface and blending it, but when I try to join the surfaces, the ‘crinkle’. I have been trying for a few days and am not sure how else I should approach making this volume, any help would be appreciated, thanks!

I’ve attached the file here if anyone is willing to give it a shot. One side is an attempt to blend and another is just joined without blending. Thanks!pill shape tray.3dm (211.4 KB)

Hi Gushingg - the surfaces are tangent at the simpler end - that is OK, no gap, just a change in curvature - you can make it look cleaner by changing the meshing settings in DocumentProperties > Mesh page to Custom and set ‘Max distance edge to surface’ at say .01. If you want it really smooth, the ends cannot be arcs (revolves) they’ll have to be a little more complex and be curvature continuous with the straight part.


Hi pascal, what method should I be using to make it curvature continuous? And what method would be the best? Do I have to change the way I construct the line work and structure? I am always having trouble with surfaces like this and would like to get better at making such surfaces. Thanks!

Hi Gushinngg - the blend might work, but I think you may want to modify the profile curve so that it has a zero-curvature at the center of the object - since you have a zero curvature segment (the extruded part) you’ll get a clener result, I think if the curved part also straightens right at the center of the revolve as well:

That will help it in the center, then I think making a transtion surface to the revolved part may be a good way to go (blue surface):

Something like this, maybe -
pill shape tray_PG.3dm (68.8 KB)


Hi pascal, thanks for the help so far, but just two more questions

Firstly, wouldn’t there still be a slight discrepancy since it is revolved and joined to the extruded surface?

Secondly, what if the profile is not allowed to have a flat surface in the middle?

Also what is the cause of the weird surface between the two pieces?

Hi Gushingg - the idea is to have the middle, blue surface act as a G2 blend so that it is curvature continuous with the extrusion at one end and with the red revolved piece at the other. If the profile cannot have a flat, then the join cannot be curvature continuous at the very center - the revolved surface will have non-zero curvature at the center - that may or may not be a problem in real life.
Making a transition that cuts off the center of the revolve, as you had in your original file, is another approach of course - that might be fine too - I think it maybe needs to be a little deeper on the outer edges than you had it - maybe a little bit dog-bone shaped.

I get this for a Zebra on the example I made:


Ah that explains a lot about the surface issue, thanks! Guess I will have to practice blending more.

The zebra is really different, could there be something wrong with my settings? Why does it look so smooth on yours?

It’s possible - I joined the surfaces and I always adjust the mesh for Zebra and all of the analysis modes to make a very fine analysis mesh - a quick and easy way to do that is to set minimum initial grid quads to a large number, like 5000…

(Do this for analysis meshes only, it would cripple the display to have such fine settings on the display meshes)

Oh, that helps smoothen the zebra out a lot, however the surfaces still do not match up. It the issue only is on the red surface for me.

I’m not really sure if this what you are complaining about, but if you look at the render mesh (extract RenderMesh) there are a few long skinny triangles that disrupt the light reflections.
If you adjust the “Maximum aspect ratio” in the mesh settings that may get the appearance you want.