Mold Making Rhino

Hi all,

Motivated by Kyle’s video in youtube about mold making with Rhino, i am trying to identify Rhino’s capabilities in making mold out of complex organic shape model.

  1. I have successfuly translated a mesh into solid:
  2. Made the Ribbon offset by following step by step process.
  3. I closed the surface an inner patch of the parting line.
  4. I tried out to boolean the 2 solids but it keeps failing.

Can someone advice why is this happening? I am sure that this is my lacking of knowledge and not the software but i cannot find the solution.

Thanks in advance.

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If you select the shape after patching the hole, is it a closed mesh? After that, did you try MeshBooleanDifference? If that fails, then pls send the file for inspection.

Yes, if i understood correctly it was a closed polysurface.
The models are polysurface not mesh.
I am assuming that the issue may be the Brep solid “head” file?

Here is the file, please excuse the sloppy layer cascade. (11.1 MB)

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It’s not clear from the model and description what you are trying to do. But if you run intersect between the two objects, you will see you get multiple (and not so clean) intersection curves. That’s the root of the problem.
Since you made a ribbon surface based on the original object, the intersection is going to be more or less on the edge of the surface, and the ribbon surface itself is messy as well. If you can simplify this surface there is a much higher chance to make this work.


I’m not seeing it.

I don’t think those are solid. But boolean doesn’t really require solids per say.

Not sure why you zipped an stp.

Ok I see the solid now:

interesting :thinking:

hmmmm :face_with_monocle:

Yeah I’m surprised it failed to boolean:

still checking.

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Point given :smiley:

In general i am trying to make a mold out of this “head”.
I dont know if the path followed is the correct to do so, if not (which is for sure) you are welcome to show the way!

Specifically, what i am trying to do is to “boolean difference” from the model “block with the shut offs”, the “head” model but it’s failing.

as mentioned, there are multiple intersections between the two if you run intersect. Try making the top surface of the shape you want the cut out of as simple as possible, and avoid any seams running close to on the head surfaces. One way you could do that is to replace all the top surfaces with a single surface. Maybe drape could help there.


I’m seeing a couple problems here.

One being the intersection point isn’t necessarily ideal for there to be a seam right at the point of intersection if you’re trying to boolean the two poly’s.

I think the seam should be created from the boolean, not necessarily prior to the boolean.

Also, the main object appears to not penetrate fully into the mold piece, but instead misses it per say.

The mold piece needs to encapsulate the whole backside in order for the boolean to capture the whole side the mold piece is intending to capture.

The ‘seam issue’ is less of a problem than the fact the backside of the part doesn’t fully penetrate the mold piece – imo. It’s possible if this other problem was solved then it might work.

Basically the part to be molded looks to be intersecting the mold piece twice, instead of once. And Rhino is probably not happy with that :sweat_smile:

I could be wrong though, Rhino might be less happy about the seam already being at the main point of intersection :sweat_smile:

Here’s another view:

So, step 1 would be to make sure your parting-line is exactly how you want it to be.

Then step 2 would be to split your part right at that line.

You might want to use Rhino8 new draft analysis parting line features.

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Yes, thats for sure that Rhino is not particuarly happy with my inputs there.

The strategy to be followed was planed as follows:

  1. Boolean intersection (without deleting the input). That way i would fill the gaps.
  2. Boolean union for the “Shutoffs” with the “gaps”
    3)Boolean difference from the (shutoffs+gups) the (head).
    And then i wakedup! :rofl:
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Wait… :open_mouth:
Is this possible to split this part right at the parting line???

Yeah, i tried to reproduce the parting line from the Draft analysis feature but it was outputted as many separate lines and discontinuities.

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Oh I see.

… There should be a way to add the curves, but I ran outa time.

I’ll bbl.

Yes, I’ve tried numerous times without success. I couldn’t achieve a clear and continuous parting line, but here’s what I did:

  • I joined the curves.
  • Rebuilt them for a more uniform parting line and deleted the input.
  • Tweaked it a bit to come closer to the edges.

Despite searching extensively on the forum, I couldn’t find a thread that demonstrates how to split a part for molding. :disguised_face:

On a positive note, I want to highlight that this is a vibrant community, and your prompt engagement has been a pleasantly surprising aspect!

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Drape looks pretty handy tool! Thanks.

The blue crv is the one I ended up with using the draft analysis feature, which would still need some work. The orange one is yours that you already provided, and I surmise you already have a fair amount of work into it. I can see they’re really close so I’ll focus on using the one you already provided.

I’m indeed going on a bit of a tangent here, cause I’m focusing on your parting line, while I could instead focus on your ‘ribbon offset’, but I guess I’m back tracking cause I feel like your parting line could be refined to potentially take a slightly different approach or even enhance the approach you already took.

Next I’m going to improve the ‘render mesh’, but here you can see that the parting line doesn’t follow the part as closely as it could.

These are approximately the settings I like to use with ‘render meshes’ and mesh conversions in general. Sometimes I change a few of the settings for unique situations but this is basically my standard parameter configuration for this, so I can have a nice accurate visual. Especially when analyzing parting lines relative to the geometry with which they reside:

Now that I’m thinking more about it, I might use your ribbon to make a new parting line. I could try modifying this original parting line and ‘pulling’ it closer to the surfaces and such, but those many surfaces add alot of complexity. The ‘pull’ command might not work very well. So, maybe an intersection of the ‘ribbon’ might be the best approach. I’ll see what happens…

I got to order some tooling for a colleague bbl.

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I feel that you r make it way too complicated and at the same time don’t spend time where it’s needed.
I made a small example that shows how I generally create a mold. I deformed a simple part so the parting surface would be more a challenge.
Mold example.3dm (8.6 MB)
Every step is represented by a layer.

  1. Make sure you forget word boolean. They are useful tools but they have their place. I use them about once very other month.
  2. Check your units and file tolerance. Before you start because there’s no way to go back.
  3. Using the draft analysis, generate a parting line, like you did. But use it as a guide. Check how I tweeked it so it sometimes follow a surface edge and other times it goes over some “zig-zag” that would prevent a clean parting surface. The goal is to have a parting line that stays on the part .
  4. Copy the part two times to have a top and bottom cavity.
  5. Trim the part with the parting line, keeping the bottom of it. You will have to extract some (or all) surfaces to get it to trim.
  6. Repeat with the other copy of the part but keeping the top. Save :wink: Join the two halves of the part; if a closed polysurface is the result you’re doing well, if not investigate. Undo the Join.
  7. Generate the parting surface. You can be lucky and get a valid surface with Ribbon. Second try is a loft between an ellipse and the parting line. But most of the time you’ll have to use Sweep2: one rail is the parting line, the other is a simple shape outside the mold (here I use an ellipse) and draw straight lines between the two curves. The placement of the lines is to ensure the parting surface won’t fold over itself. Several tries may be necessary.
  8. Trim the parting surface with the mold. Split the mold with the parting surface.
  9. Copy the parting surface. Join one copy with the bottom cavity of the part and the bottom half of the mold, the other with the top cavity and top half of the mold.
    Good luck!

others have chimed in here with good info, but I’ll add… when I was doing this type of work, we always split the part with the parting line so we have the halves of the parts 1st…

then ribbon offset from the edge of the part, then create the rest of the molds from that…

the boolean at the end is not necessary, when you split the original part to start with.

of course, this all becomes moot if your molds can be cut from a mesh, simply shrinkwrap your result and do a mesh boolean from the mold with the original part.


@Babis_T For this shape, since it has a very irregular outline, this approach might also be useful: creating a patched surface from a rectangle and the parting line:

parting-surface.3dm (450.6 KB)


Big thanks for the mold-making tips! Got some awesome advice on the forum. I’m going to try them out tomorrow and will loop back with how it goes. Your support is awesome!


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Here’s an example:

Getting a bad opening here though so might increase density of the ribbon and try again:

I got another bad intersection here:

So, from here I’d have to really put more time into creating a cleaner partingline/ribbon etc. to then refine a nice intersection for a final parting/splitting-line.

It’s definitely doable, it just takes time. I was just trying some shortcuts to see if I could do it faster.

The ‘splitting ribbon’ is key.

Ironically, this type of work is literally and in fact exactly how I started using Rhino every single day, day in an day out in 2008/2009.

Back in those days I was a beginner (with Rhino), and one of the first big jobs I did with R4 is, I spent about 1-2 weeks building specific ‘splitting ribbons’ on a particular-highly-classified-mesh-model using R4.

At the time, I didn’t know for sure if the mesh would split successfully when I was done, but I had faith that it would. And low and behold after I was done putting the necessary time into the ‘splitting ribbons’ it worked! and the mesh indeed split! I was so excited of that success in those days.

Of course in those days, I was using the ‘fin’ command though, to get the surfaces upto a point, and most likely modified them using the control points and ‘moveUVN’ etc.

Now that I think more about it, I think I had to literally sketch every parting line by hand onto the mesh or something and do some type of offset. I basically remember making dozens of parting lines all meticulously by hand in order to split a particular mesh. It was crazy at the time, especially considering how newby I was with Rhino. :smiling_face_with_tear:

So, my point is, this is basically how I know the task shown here in this thread will work – it’s simply a matter of time, and there will be some beautiful parting lines and the part will be split :smiley:

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Hello Marc,

What a detailed process along with the consept mold model given? Wow :saluting_face:
I have been trying now for almos 4-5 hours to replicate the Trim as you did on your model, but nothing.

I assume that i dont fully understand on how the trim tool is working, so i can reproduce / tweak a parting line in a way that i can get a result in my model. (Nevertheless, i manage to reproduce the trim on your model)

My last attempt was the “Interpolate curve on surface” creating a curve from one surface to another by following the “mid” color of the “DraftAngleAnalysis”. After a few hours effort, i got desperate and gave up on this. :melting_face:

Do you think it may be the model it self?

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