Trying to create a hollow solid with a wall thickness starting with a closed surface created by revolving a curve. Having no success with Shell or OffetSrf or creating an offset surface.
Curve to revolve.3dm (127.0 KB)
A - Revolve the curve and offset the surface.
B - Offset the curve and revolve two curves.
Select both surfaces and run _NonmanifoldMerge
Why are you trying to do this?
Why is this not a solid? This is the same result I get with using shell and offsetsrf, two separate surfaces.
What do you mean?
Itâs a closed surface.
Did you run _NonmanifoldMerge?
As @martinsiegrist says, you need to run _NonManifoldMerge, but that isnât sufficient. After running NonManifoldMerge you need to take a couple more steps to complete this:
- Run _CreateRegions on the non manifold object.
- That will leave you with a polysurface and some surfaces. Delete the surfaces, leaving the polysurface which will be your hollow solid.
NonManifoldMerge combines the two surfaces but doesnât flip the normals of the inner one. This leaves various problems, including: booleans donât work. Wirecut doesnât work, Volume returns the wrong result (it adds the inner volume to the outer volume instead of subtracting it.
CreateRegions sorts most of this out.
HTH
Jeremy
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Iâm curious, why do you need a hollow shape with no opening?
Thank you. That worked. I am surprised that the _shell command doesnât do all of this.
I want to be able to properly show the solid wall when showing cuts through the shells.
By cuts do you mean drawing sections or do you mean openings that are part of the ultimate object?
If you are making openings then you donât need to go through the above rigmarole. Indeed, before NonManifoldMerge etc the âold schoolâ way of creating a hollow solid in Rhino was to create a solid (i.e. closed) outer surface, boolean a microscopic radius cylinder out of it, too small to appear in a rendering, but long enough to intersect the planned inner surface, then boolean out the closed inner surface. That thin bridge was enough to meet the criterion that all the surfaces of a polysurface had to be connected. Rumour has it that that may be more robust than the non manifold method.
If you are making big openings then the thin bridge is redundant of course.
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well Rhino is not a solid modeller, we have solid tools in Rhino but that means though something similar actually something entirely different here, i am not equipped to explain the differences. i am sure you can look it up.
If Rhino would easily allow a seam to be inside and along one rotational axis that would not be a problem i guess, right now most of the tools complain or just skip the geometry on the inside or just create two independent objects.
but Rhino has one last trick up its sleeve without making a microscopic hole as mentioned above or to create non manifold edges etc, though it might be a bit unorthodox:
create a closed profile and a circle then use Sweep1, it will create a closed object with an internal surface that is properly connected. i have no idea why this is not possible with revolve or rail revolve and why some strange mechanisms have to act there. i am sure there are reasons but right now with Sweep it still seems to work.
swept.3dm (195.5 KB)
Rhino IS a solid modeler.
The definition of a âsolidâ in CAD is ONE set of joined surfaces enclosing ONE volume. Thatâs how you know you have a solid, thereâs no such thing as working with âsolidâ volumes, there are no voxel-based CADs. Non-manifold shapes are also illegal to make in âsolid modelersâ because you could never machine such a thing.
But the world has changed: now you can print itâŚ
Only via FDM, if you donât need infill, if weâre being pedantic.
Well, Iâm sure youâve noticed, but FDM - declared âdeadâ a number of years ago with the advent of resin-based printers with higher resolution, is now everywhere⌠because people like BambuLabs managed to make FDM (or FFF) with a speed, resolution and low cost that works for a lot of consumer applicationsâŚ
Um guys I have as much 3D printing experience as anyone what does this have to do with the subject at hand?
Non-manifold geometry is not allowed normally in ANY CAD, for the reason that a)the mathematical definition of a solid is a manifold shape and b)such shapes are normally what one would consider ânon-manufacturable,â and a solid inside another is not the only non-manifold shape, and the others arenât âmanufacturableâ at all.
without pretending that i am a professional mathematician, i can tell you that there is a whole world of a difference between a nurbs and a solid modeller. solid in Rhino means something else than solid in Solidworks for instance.
also look at the example i have created, there is no nonmanifold edge, it simply has the seam inside where you dont see it.
talking about prints, in the end its just a slicer and an extruder or a laser or a led created light beam that follows a path.
No there isnât. Itâs just using a different NURBS surface kernel. The ONLY definition of a âsolidâ is a hole-free collection of surfaces that donât intersect. The way âsolidâ modelers (used to) never let you do anything that left the model in a non-solid state was a deliberate part of the UX design, not the math.
i think you might be interpreting something into how others might see the definition of solid modellers. maybe there is some overlap in solid modellers and nurbs modellers but by definition they are different. Rhino is not a solid modeller per this definition.