Hard surface confusion - slicing into convex/concave surfaces

Hello everyone.

I’m been learning how to model in blender for quite a few years now but achieving particular meshes/topology still really confuses me. I am hoping someone can help me understand how certain meshes can be created.

The render below (by Rizon Parein) is the kind of model/mesh that really confuses me. I don’t understand how a slice can be made through a convex or concave surface without creating horrible, uneven topology.
Forgive me if the description of my problem is confusing but if there is anyone out there that understands my confusion please speak up.

I know of the boolean modifier but that doesn’t help as it doesn’t seem to help with the creation clean topology.

Please help! :slight_smile:


Well, model the cuts in from the start and that shouldn’t be a problem.


Are you sure those are SDS (subdivision surface) meshes at all?

In a NURBS modeller these shapes can be done in seconds (well, minutes…) - just export them to a render engine of your choice afterwards and voilà! Topology would also not be immensely important in that case, because the NURBS modeller would export the meshes with a custom vertex normal map that provides the smooth shading. Unfortunately dealing with those custom vertex normal maps has never been one of Blender’s strengths…

Unfortunately the Boolean Modifier IS the easiest way to get the line of intersection. But you will need to fix the various problems inherent after applying it. (There’s an addon floating around out there but I’m not sure it works in current versions of Blender.)

One way is to do the Boolean, apply it and then use the resulting object as a guide to construct the final one with the curve in the proper place from the beginning.

And for the illustration in question there’s no reason not to have used a very high resolution mesh and just not do any Subdivision.

If he is using it in his portfolio you can be pretty sure that it’s not something super quick to do. I’m pretty sure that’s a vector drawing, not 3D.

Thanks for the replies.

I spent today considering your answers. JA12, your reply opened my eyes to what I should be modelling. You made me realise I need to consider the flow of the mesh earlier in my modelling. Thanks.

IkariShinji. The methods you mention, are they C4D? That sounds interesting. Thanks.

DruBan. I had a go at your suggestion and got a little lost. It did however, lead me to a new approach which I’m quite happy with: I modelled a bezier around the convex mesh then used the knife tool to cut where I wanted the intersection, then modeled the inside of the cutaway using beziers that I later convert to mesh and fill.

Here’s one of my results - not quite on par with Mr Parein but I think I’m getting there

Yeah, C4D has some nice NURBS functions, but being a hobbyist I find it just too expensive. I use MoI3D for all my NURBS needs.

I prepared a little video showing the basic workflow from MoI to a polygonal modeler and renderer (.mp4, 17 MB) - roughly 2 minutes to the final mesh and another 4 minutes for export, import and basic shading:
Sorry for the “silence” - I caught a cold and the coughing was so bad I had to turn off the microphone. Why did I import the mesh from MoI to modo and not to Blender? Well, because Blender sucks at dealing with imported CAD data (I’ll leave it at that, because I am tired ranting about this).

I hope this leaves you a bit less awestruck about this kind of hard surface modeling…:wink:
There are always several ways to skin a cat. Of course modeling those shapes in a polygonal modeler like Blender is entirely possible, but it is also tedious and lengthy while NURBS can be a real timesaver.

I was quite happy with my results above until I realised the shape I was cutting through was only convex on one axis (I hope that makes sense!). This meant when I came to slicing into a sphere or any other shape that was convex on multiple axis triangles started to appear.

After a bit more googling I found this thread:
http://lightwiki.com/forum/modeler/39-subdivisionmodeling-com-the-pole?limit=10&start=20

About a third of the way down the page Probiner mentions the problem I have had, but he goes into more detail and suggests a fix.
After having had a bit of a think about his post I realised the problem can be solved by turning the edge flow away from the slice.

This is the first result I came up with after trying this method of redirecting flow:

Here’s a render