Blending surfaces

I’m attempting to build a seat and I can’t seem to get the two surfaces to blend to look like a natural fillet. Any suggestions??

I created the surfaces using NetworkSrf, which has been successful for me in the past, however the ends of the surface always seem to get a strange anomaly that I’m unsure how to resolve.

Any help would be greatly appreciated!!


I’ve attached a copy of the seat surfaces, if you’d like to take a look.

seat_needtofillet.3dm (721.0 KB)

Yeah… I’d try to find a way to make the shapes that does not force the surface to pinch in at the ends - a more rectangular shape with the oval perimeter trimmed, would be my choice. The curves are fairly lumpy and ‘all over the place’, especially the perimeter curves - is that a design decision, or should it be cleaner, ideally?


FWIW, it looks like it’s two shapes, try a solid offset, it’s an option for OffsetSrf, there are two surfaces there.

If you fill those as a solid (I don’t know how a novice too), then it will fillet but the solid offset is simple to test, arrows appear of which side, I flipped & offset 1mm & it thickened, it would chamfer at 0.2mm but not fillet.

To smooth the curves the tool I like is on the points tool button menu for the handlebar cursor, it can adjust in-out to the axis it represents and alter the hulls in two directions [a midpoint on the main axis is the in-out, the end is tricky to adjust, suggest saving under new names when something works].



The reason this is giving you so much trouble is that the very approach from square one is flawed. You’re trying to make the entire seat interior or exterior from one single surface, and just from a philosophical standpoint, the problems you’re having a direct result of that. Notice how your isocurves pinch in at the sides of the chair? This is called a singularity - meaning the points all end up stacked on top of each other there. There are a FEW instances where a singularity is fine, but this isn’t one of them. You’re essentially trying to describe a circle (the smooth perimeter of the seat) with a rectangle (NURBS surfaces should ideally be 4 sided).

There has been some confusion/discussion in the past on here as to when you should use trimmed surfaces, and when you should use untrimmed surfaces. This is a perfect example of an untrimmed surface being the wrong approach. If you look at the attached screenshot, you’ll see how I would approach this from a “patch layout” standpoint. Really, when you get down to it, the very first thing you should do for every model is try to imagine how your patches will be laid out, and where if needed you’ll have trims.

You can see that the bottom of the seat is made of one surface, that is trimmed by a second surface that forms the back and sides. Then, I’ve trimmed the upper corners of the sides so that the entire thing is smooth all the way around. Now, I’ve done this without any regard for the finer details of the shape you’re looking for, but this illustrates the correct approach to this problem. This surface will offset very easily, and will blend between the inner and outer surfaces with no problems.

Another point I would make is that for smooth/organic shapes like this, your best friend in the entire world is point editing. By using NetworkSrf to create your base surfaces, you’re really locking yourself into a terrible workflow, where it’s just curves in -> very dense/uneditable surfaces out. That’s probably a bit more of an advanced topic to tackle here, but the way that NetworkSrf has become a default/go to command for so many is baffling to me, and I wish someone had told me far earlier “don’t use NetworkSrf as a go-to.”

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As you can probably tell, I’ve only been working with Rhino for a short while. So the advice is great.

I work for a man by the name of Wendell Castle (he’s a well-known furniture maker/sculptor) and we’re currently trying to clean up scans of his hand-built models so we can easily carve the work on our 6-axis robot and then “shrink” the models and use them to print 3d models. My job is to make the forms as close to the original intent as possible, I’ve figured out a good workflow for the pods, just trying to figure out how to maintain the sculptural integrity of the seat forms. For Castle’s work the “rim” of the chair becomes a very important part in the end design, which is why my curves are a little bit odd looking.

Any suggestions on a better workflow? Like I said, I’m new to Rhino and haven’t built much from scratch, so details/commands would be greatly appreciated!!


original_scannedmodel.3dm (5.2 MB)

Wow, that’s uh, a lot to tackle! As someone who has been using using Rhino for about 7 years or so, and does laser scanning, I can tell you that perhaps the hardest thing to do is to convert sculptural style work to NURBS from laser scanned data.

Honestly, what I would propose would be to use a completely different technology. Since you are looking to scale them down for 3D printing, converting to NURBS is not actually necessary. All a 3D printer cares about is whether what you’re asking it to print is “watertight” - free of gaps or holes, so that it describes a closed solid. The problem with raw laser scanned data is that - as you can see in yours - there are often gaps or holes. Since you’re not looking to really EDIT his art (just scale it), really the best way to get from raw scan to 3d print ready…is to simply use a mesh/polygon editing package to make it watertight, and maybe smooth out some artifacts from the scanning process. ZBrush does a fantastic job of this, and so fast it’ll make your head spin. Seriously, there have been some projects very akin to yours that I’ve done, and I handed them off to Kevin Pasko (a top notch ZBrush dude) and he was able to finish them off in an astoundingly short time. I know you probably have a lot invested in this personally, but really, truly, Rhino is not the best fit for this type of job. I can put you in touch with Kevin if you want - he actually works with Kyle Houchens who is a moderator on here and works for McNeel as well. I love love love Rhino, I truly do, but this is a ZBrush job in my book, hands down.



HI Bridget - how much shrinking? Maybe cleaning up the scanned mesh, if needed, and simply printing that would be sufficient?


One other suggestion - if that version is the highest resolution version of the raw data you have, you might want to try tweaking your laser scanner settings (or tweaking your laser scanning vendor lol) - Just the areas that form the blend between the inner and outer surface of the seat get a bit chunky/faceted. If it was me, I would use a higher resolution scan. It’s not like night and day, but would be good to have.


@skyg – My predecessor attempted to use Z-Brush and basically butchered every form that was given to him, so we’re hesitant to go back to that.

@pascal – I’d love to simply fix the mesh, however we’re looking for a higher quality surface so we can print it in metals and polish them for possible sales. It doesn’t have to be perfect, just has to look close to the original model.

ZBrush is hard. Really hard. I can’t get my head wrapped around it. I know Kyle gave up on it. But Kevin is some sort of savant with it. And he would absolutely be able to polish/smooth the surfaces for higher quality prints. I can’t post what Kevin did for me due to NDA’s and such, but I still stand by my assertion that this is a ZBrush job, as long as you have a good ZBrush operator. If I was to estimate this job in hours for Rhino/NURBS, I would say it would take roughly 10X the time it would take to do it versus in Zbrush, maybe closer to 20X. Seriously, not exaggerating here.


I was able to get some usable surfaces… somehow. Is there a way to merge the surface edges? Or to create curves from the surface edges?

Hi Bridget - MergeEdge, MergeAllEdges, DupEdge, DupBorder.


Hi bdsheehan,

I did this in very short time. It is a quick shrink wrap around your scan. I used some button click/software tools to clean this up in Zbrush. Accuracy and refinement past this are all pretty simple. This is 3d printable. I work in a high end 3d print shop. I can clean this up and get you a quote if you want.

Is this in the neighborhood you are looking for?

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I see Kevin already offered you a solution.

Depending on your requirements, and if you are familiar with subdiv modeling, another way to do it could be by using a polygonal modeler and retopology tools - the shapes are rather simple and suitable for this type of approach. In this way ou can create a very minimal polygonal mesh and subdivide it to smooth it and increase details while automatically constraining it to the scanned geometry.

I have done a part in Modo very quickly- but this can be done in many apps, including Blender.

If you have access to T-Splines, you could use it for the same approach and/or for converting the mesh to NURBS (on the right in the picture below) for adding final cuts or details using Rhino.

Just another alternative.


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