Creating groove at the middle of the mesh

Hello i have trouble with the mesh i am working on it. I need to create triangle shape groove at the middle of the inside face of this ring. I tried to extract wire frame and join curves at the middle but it didnt work properly. Is there any way to draw a curve at the middle of this mesh and use it as a refrence for creating groove?

That’s a really simple shape, so I would re-make it as NURBS instead of a mesh. I would find the center as near as possible, cut a section through the object (that goes through the center) and re-do section curves up so that they are simple and clean, then re-revolve the object so it is a clean NURBS polysurface. You should then also be able to create your groove as a revolved object and subtract it from the main object - or, even incorporate the groove in the main profile section before revolving it.

You will just have a much better time working in NURBS than meshes, and you can always convert it back to a mesh afterwards, if you really need a mesh for some reason.

Thanks for your answer. Acctual the real object i am working on is glasses and when i convert it to nurbs, it does not come properly. I couldnt upload the real object pic sorry for that.

Do you have a low poly version of that mesh, because high poly meshes are a nightmare to operate on?

Anyways, hard surface modelling mostly relies on two principles: creases and edge loops.
Creases as far as I know aren’t available in Rhino, but they behave like this:


Edge loops, when inserted near an existing edge turn that edge into a harder one (when subdivided). I’m not sure if Rhino can do that either?


Rhino isn’t the best program for mesh modelling and manipulations, even though it can handle meshes. I’m mostly using Blender for that these days.

For your specific case, the best way would probably be to select the edge that you want to inset and simply move it inwards, thus creating a triangular ridge.
Optionally you could also bevel the selected edge loop, and then move it inwards.

Hello, thanks for your answer. I did that to, extract one edge curve and use it but this time, there are some places that goes in the mesh and some place that stay out the mesh so i could not use it as well.

So you don’t have a low poly model? And where exactly do you want to make the inset?

Acctualy i dont know if it is low or high. I am trying to create groove on the frame so after print it from 3d printer. i can put lenses on it. This is the file. I would be very appreciated if you can check it
P1-0002.3dm (9.6 MB)

OK, considered low poly is usually a non-subdivided, simple mesh with just enough geometry to define a rough shape. Yours however is a high poly model with lots of faces which is hard to manipulate.

Like @Helvetosaur mentioned above, your best bet is probably to remodel with nurbs, especially since you need geometrical precision for stuff like fitting glasses inside a frame. Meshes aren’t that reliable, since they’re always just approximations of a form.
Once you have the nurbs model you can use Boolean operations to cut out the groves for the glasses.
For 3D-printing, you can then export a STL-file from your nurbs geometry.

Thank you very much for you help

Did you create the mesh model? If so how did you create it? Ir did you import it from elsewhere?

How is the groove located in the frame?

Create a NURBS curve on the mesh at the desired location of the center of the groove.
Draw triangle of the desired cross section of the groove. Make the triange normal tot he curve and have triangle extend above the groove.
Sweep1 the triangle around the curve to create a NURBS cutting object. If the swept shape twist add additional triangles around the curve to control the twist.
Mesh to convert the NURBS object to a mesh
MeshBooleanDifference to creat the groove in the frame mesh.

Hello, i import the mesh from somewhere else. I have trouble the creating center curve for the groove at the middle of the frame. I create one which is not %100 on the frame. ıt is not touching to the frame at same points and go through inside the frame in some points.(ı create this curve via extracting wireframe and join the curves which are approximately at the middle.) I try to illustrate the problem with pictures.
I also try to increase height of the crossection of the groove but in this time there are roughness at the edges of the groove.

curve3 curve1

How precise is the depth of the groove reqired to be?

To check the deviation of the curve from the mesh:
Use Divide to create many points on the curve.
PointDeviation and select the points as the object from which points are to be extracted, and the mesh as the object to check against. Set the values in the pop-up based on your requirements.

Note in V7 the curve does not have to be divided into points before using PointDeviation. The curve can be selected in the PointDeviaiton command as the object to extract points from.

This is the crossection of the groove, to be honest i could not understand completely how to do:)
Edit: i see what the pointdeviation command does but still could not the points on the mesh i mean clound not reduce the distance between points and mesh to 0.

Edit2: at some points, the hair is not visible and i cant move that point on the mesh

I have another problem now, i have 2 meshes that i want to boolean difference. But it doesnt work. The mesh i picked up secondly disspear all the time. I check both meshes with the MeshRepair and result is This mesh is a good mesh. Is it because the rhino cant manipulate the mesh objects?

Hello - do both meshes pass the Check command? Mesh intersection operations are not super reliable in V6 but should be a lot better in the V7 Beta -, you might give that a try.


Hi, yes both meshes pass the Check commands. Thank you for advise, i will try it and update the post.