From ZBrush to T-Splines to Rhino Closed Solid Polysurface

I wanted to CNC some faces, or gargoyles out of oak, and was trying to find a way to do this in Rhino. But after seeing some tutorials with Rhino 5 and T-Splines, that also used Zbrush to add some fine detail.

This is my test: First I modelled a North Wind style face (quickly in ZBrush) at a high resolution, then modified the export resolution (lower) and output it as a .obj file.

Some detail was lost but this was just a test… I then imported it into Rhino 5 with a T-Splines plugin. It imported the obj file as a Rhino Mesh (but one of all quads) which was accepted by the T-Splines Convert Tool when I made it a T-Splines Surfaces (thing). I then took it back through the T-Splines Convert process and made it a Closed Polysurface Solid.

To which I Split the back and Unioned it to the Poly Rectangle, quickly and without error.

The 3dm file is here:
Regards Greg


Why do you at all convert to Nurbs? The high res mesh should be just fine for milling.

To incorporate it with a frame that I fashioned in Rhino, and have them cut at the same time. To bypass some of the issues I have with combining meshes… To show that even T-Splines or for that matter just one piece of software can do all things, and to show a workflow that some jewellers were using to add detail to there projects.


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Here is the tutorial I refer to:

Regards, Greg

Hi, MrPelican, i couldn’t find a way to import mesh via T-Splines. What is a t-splines command to do that?
Thank you!

The mesh must be Quad based (4 sided poly) with few if any triangles. The tool you use to convert is the “convert” tool (found in the T-Splines "Create Set of Tools) (that has two directions NURBS and mesh to t-splines and the reverse).

You can either import an OBJ file (mesh) into Rhino 5 from another program or model service or generate a NURBS or mesh in Rhino5 and convert it to T-Splines with the Convert tool.

The importing of the file is done from the Rhino 5 File/Import. The conversion is done with the T-Splines Convert tool.

Also if the mesh has triangles try the “QuadrangulateMesh” command from Rhino 5 to reduce or eliminate them.


Sorry for the late reply! I see you had your reasons.
Often times I just wonder why people do certain things… Conversion of a mesh to Nurbs doesn’t improve anything. It neither makes it more accurate or more watertight, nor does it improve its milling or 3D printing properties.

I’ve never had much luck bringing even moderately high poly meshes in to T-Splines from ZBrush. The conversion to T-Splines and nurbs doesn’t seem to work. I can bring in Maya type low poly files though and they work fine.

That said the newest version of ZBrush due out next month will have major improvements to it’s low poly tools that should make a big difference in this work flow. I generally just do everything in ZBrush though… I just use Rhino for things that need to be very accurate or can’t be done another way.

T-splines was never intended a tool to convert high poly models to nurbs. The purpose of T-splines is to allow a relatively low polygonal representation to modify/deform a nurbs model. Integrity Ware’s PowerNurbs/PowerSurfacing produces a similar result with similar limitations.

High poly meshes can be converted to nurbs by Geomagic and Rapidform software.

T-Splines did a Webinar a couple of years ago turning a million poly mesh to nurbs and performing Rhino functions on it. I’ve never been able to replicate that, but also have never needed to.

I spoke directly with T-Splines a few times a while back (pre Autodesk). They indicated that a few hundred thousand polys was the maximum. Maybe they improved it?

Here’s the link to the 2011 Webinar that I was talking about-
ZBrush has come a long way since then and will be taking another leap very soon.

The reason I posted the workflow from ZBrush to Rhino (via T-Splines) was because I was having difficulty with “Organic Shapes” in Rhino. I do not expect Rhino to do everything, in terms of modeling any more than I expect ZBrush to do it all.

Also my CNC software resides in Rhino (as RhinoCam) so it is important to get the Organic shapes (that take no time in ZBrush) back to Rhino in some workable form.

Also since I am working in Hard Wood, I find the resolution needed to be medium to low poly count. There is always sandpaper to remove low resolution poly edges (which I have never seen), since the CNC software and machine has its own resolution limit (unless you are willing to let it run for 10 hours).

Regards Greg

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Thanks for that link.

Its not clear I was told a few hundred thousand polys max if it could handle millions. Although in retrospect it may have been because it was still a 32 bit application at the time. I made the inquiry before 2011, when the video was made. However, the head shown in that video has only 500,000 polys (as shown in ZBrush)

Perhaps if the detail has high frequency (like noise or texturing in the surface geometry) or is data coming from a 3d scanner, that may be pose an issue with a high poly count as compared to a low resolution mesh that has been subdivided to a higher poly count, where the topology would be fairly uniform.

I would like to hear from anyone that has experience getting a a relatively quick, useable nurbs model from a 3d scan (or a sculpture with a lot of surface texture in geometry) using Rhino and T-Splines.

I understand that in any case, you have to start with a good mesh, so no holes or poorly matched/registered surfaces if from multiple scans, so there may be significant time to prepare the mesh for a good conversion.

Conversion of a mesh to nurbs DOES improve its milling properties, in that many milling services will refuse to mill from a polygonal representation.

I have been told on many occasions that a mesh is simply not an acceptable format for cnc milling, as recently as a year ago. Having machined meshes with a million or more triangles on a cnc mill myself, over 10 years ago, I know now that any time I get this response it is because of a business decision, rather than a technical limitation of the equipment and software.

I note that when bringing in a closed quad mesh from ZBrush as a OBJ file, that Rhino had better success with the “MeshtoNURB” command then did the “Convert” Tool from T-Splines. And that the closed polysurface it derived went through a Boolean Difference with Solid success, and easily. In contrast, I have had issues with the Mesh related commands accomplishing the same result easily.

To my way of thinking, the Detail possible with Quads will not achieve the same fidelity as the naturally planar Triangle, and to even come close to that detail level would require smaller and many more quads (and its effect would bog model movement etc).


Quads vs Triangles:

Since Quads are the desired format of polygons for some printing (3D) options. I thought I would investigate the export and re-mesh options when developing a model for Rhino 5 to work with (from Zbrush), and the fidelity retained (or lost) in the process. (BTW, when using ZBrush… they call there “Models” … “Tools” and it seems they call there actual tools “Brushes”.
The 1.3 million Quad and the 2.6 million Tri are too much for most Boolean commands…(35 minutes to an hour plus, if you have the memory) But poly counts of 125,000 or less worked in a timely fashion.

And one of each so the difference is clear:


Hi Greg- if you have quads in Rhino, and you export to STL, the quads are triangulated automatically since that is what STL supports. The general arrangement is not modified in this process and no vertices are lost or moved. Dunno if that figures into your researches…


No, for 3D printing virtually all systems use .stl format which is entirely composed of triangles - as in Standard Triangle Language or Standard Tessellation Language. Quads may be preferred for creation, but at fabrication time, triangles are the rule.


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Thank you both for that understanding. I guess the reason that the transfer from T-Splines or Zbrush to Rhino is preferred to move in quads is so that Rhino can convert the quad mesh to polysurfaces? and that that would be preferred for further creation or manipulation?