Split and then loft

Hi, I am new here and new to rhino also. I am trying to split an object (a .STL object) into two pieces, add some space between splitted parts, and refill the gap via extrusion or any relevant tool.
Created a simple example below to better describe, a cube splitted to two parts using a cylinder, one piece moved away a bit, then filled the holes at splitted parts (dont know if this was necessary), and now looking a way to create an extrude from one splitted face towards to other, to refill the gap.
Thanks for any advices.

Hi @alper4,

Welcome to discourse.

Could you explain what form the rejoining should take? For example like this:

or like this:
or something like this:

It’s hard to give the right advice without knowing more…


Thanks for the reply, I am planning to make a single plane cut. I mean, I will split the object with a 2D rectangle plate, which remains parallel to ground, then will rise the upper part, and want to fill the space. The shape is like an inverted U (like a tunnel). And I want to make a cut from vertical middle of legs of U, basically. (Object is composed of triangles, not rectangular, since .STL)

I re-read your answer, I think misunderstood your question. More like may be in the first picture? Edge to edge fill. @jeremy5

Can you post a Rhino model with the actual object in it?

One way to do this in V6 might be:

  1. Use Split to split the mesh (don’t fill the holes)
  2. DupBorder the two split parts
  3. On the resulting curves, run Loft to loft a surface between them (check the seam)
  4. Use Mesh to mesh the lofted surface - use a custom mesh and set all values to 0
  5. Join the new mesh to the two other parts
  6. Run MatchMeshEdge on the joined object to split the edges at the appropriate places so the mesh is clean and closed.

BridgeMesh.3dm (483.5 KB)

In the current WIP, you can simply use the Bridge to command to bridge the two open edge loops to form a closed mesh with one command.

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@jeremy5 Here is the model’s link;

And below is what I will try to achieve. Its a sort of special purpose phone case (like a dashcam) and I am trying to fit my phone into it, printed it original size, but the bridge part on the bottom end (inverted U shaped) snapped since the phone is thicker than the model.

@Helvetosaur Thanks for the answer, I will try your steps, hope I can succeed.

Hi @alper4,

I downloaded the STL file from your link and imported it into Rhino 6 which reported:

Original STL mesh has 2001522 vertices and 667174 triangles.

This is much more complicated - and much denser - than your original example. I’m not a mesh expert but I think you will struggle with this dense a mesh in Rhino 6. For example, I cannot get it to split cleanly in the area I think you mean.

Maybe @Helvetosaur or another member of the community with greater mesh experience can be more help.


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In fact, I tried instant meshes software in hope to get something more usable, but it imported the obj file with some missing faces etc., So decided to try rhino. As you mentioned, the mesh is complicated, but what I am counting on is, the operation should be (sounds like) simple. 2D Split, move away, extrude (or loft) to fill gap. Of course, to my inexperienced eye. But thanks for the help and opinions!

Hi - if all else fails, you should be able to sub-object select (Ctrl+Shift) mesh faces along the cutting plane, then split disjoint meshes, move one part and finally fill the gap.

@Helvetosaur, followed your steps and get the following, which looks like what I want. The only concern is the black line at joined edges, am I doing something wrong at join, or is it looking normal?

uncheck Display > SurfaceEdges may be a solution.

“surface edges” is unselected already. My concern is not aesthetical, but worrying if this causes problems during 3D printing.

Tried it in the Rhino 7 WIP and the mesh split works cleanly, allowing bridge (new to R7) to be used to fill the gap:

If you have a Rhino 6 license you can use the R7 WIP, but it isn’t available if you are only running the R6 evaluation.


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Hi, thanks Jeremy, this is an interesting feature, but I am evaluating the 6. But I have managed to create the lofts according to measurements above. I hope it works flawlessly on the printer side. I want to be able to change length of the some lofts, later on. Is it possible to select just the loft area, after join applied? (via naming that part, etc. I did not join them yet)

Ok after successfully splitting and lofting in one axis, now tried another split, longitudinally, as seen below. I was planning to make 1mm splits to both sides to enlarge model 2mm in total, but unfortunately, dupborders command is creating/following some surfaces from former split too, the result is I cannot apply the loft to desired area.

I am not sure there can be a solution to this problem since latest dupBorders command is not creating the curves where I want, but still wanted to ask, if theres a way to select only open areas of the latest split meshes, prior to give dupBorder command ? (see what happens after dupborder, below)

case_fixed_Bridges.3dm (19.6 MB)

Another solution can be, scaling the whole model in one axis, but this time, fan screw holes are shifting and I dont know how to reposition them.
Any ideas?

Well, the real solution to this is to model the object yourself in Rhino using the original as a guide.

However, if after each stage, your mesh is closed, you will not get extra curves when you dup border after a split. The extra curves are coming from areas that are still open. Try MatchMeshEdge to see if you can get them to match and join.

Doing this kinds of stuff on a mesh object needs a thorough knowledge of what Rhino does with meshes, its weak spots and possible workarounds. Again you might be better off spending your time remodeling the object with Rhino surfaces. You will have a lot more control.

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