ZBrushCentral

When a cylinder pipe passes through a surface, the hole closes

ZBrush Usage Questions
#1

How can I maintain a hole when a cylinder pipe passes through a surface? I tried masking where the hole has filled in, and deleting that geometry. It looks like there’s now a hole. But when I go to print the resulting SLA, the hole fills in with a one slice thickness (or a few slices, if the model is at an angle.) Below that surface, there’s the intended pipe geometry.

TLDR: I’m making molds for casting, with high temperature resin using Preform from Formlabs and a Form2 printer,

The workflow is to dupe the original model , then inflate it, Both tools are dynameshed. I then use boolean to subtract the original file from the inflated file.

Then flip the normals in the original file, so that I get a wall and a cavity, with the inner surface of the wall matching the outer surface of the model so I have a mold that will replicate the original file, in a cast. So far, so good.

I need to put in pipes so that I can fill the cavity with metal, and also have exits for air to pass through. The Cylinder Pipe IMM Primitive brush gives me great geometry, and I can use the gizmo to bend the pipes so that they work as needed. Just leaving me with the filled in hole at the intersection of the pipe and the outer surface.

If I let PreForm do the suggested repair, it flips the normals back, and I get a solid, so I ignore the “Repair” function, and let the print run with the reported errors, which are spurious. But I haven’t been able to get the pipe to maintain a hole through the surface.

Underneath that first slice(s) the pipe still has a hole. It’s a pipe with a cap at the intersection . It’s only when it passes through the shell geometry that it fills in.

Any ideas greatly appreciated.

#2

Hello Rob!

I appreciate the effort you went to to explain your process, but I may still be confused about what you want to do. I’m not certain, for instance, why the inflation and the flipping of normals is necessary. In my mind, it doesn’t seem like this should be that complicated.

Can you not just use Live Boolean directly to subtract whatever mesh you want from your “mold” object? As long as you’re working with closed volumes (not a mesh with an open hole), this should result in a solid, closed object with whatever negative space you placed there.

If I’m not grasping what your issue is, please illustrate it further with a screenshot showing the problem, if possible.

#3

I’ve been known to figure out the most complicated pathway to any objective, so I hear you. I flipped the normals so that Preform, Formlabs software, wouldn’t make the models solid again. Just a work around. I was surprised that it was necessary!

Attached is a screen grab of the mold, with a Cylinder Pipe penetrating. I manually select the polys that close the hole where it penetrates the surface and delete them. But the hole fills up again when imported to Preform.

I’ve uploaded one shot of the mold in Z, before I remove the blocking geometry, then 3 files that show the cylinder is hollow until it hits the mold surface, when Preform fills it in where it intersects, then leaves it hollow again.

Thanks so much for taking the time to play detective! I’m eager to learn if there’s a better workflow, as well as simple adjustment that would make the problem go away.

Zbrush%20-%20Llama%20with%20Cylinder%20Pipe
Zbrush - Llama with Cylinder Pipe.jpg1276×1534 368 KB
Preform-Cylinder%20hollow
Preform-Cylinder hollow.png1336×1090 55.2 KB
Preform-Hole%20starts%20to%20fill%20w%20this%20slice
Preform-Hole starts to fill w this slice.png1310×1320 137 KB
Preform-Cylinder%20filled%20in
Preform-Cylinder filled in.png1454×1618 1.38 MB

#4

I’m sorry, I don’t understand what I’m seeing here, or what the problem is. No manual deletion of any polygons should be necessary. Use Live Boolean with closed volumes. It will preview the resulting mesh, and you can make sure everything’s ok. If you’re producing a properly closed mesh in ZB, it should be closed in your target app. There shouldnt be any holes to fill in. If otherwise, it would seem to be some sort of issue in your target app.

One note though–if youre trying to cut a solid hole with that cylinder, the cylinder should be solid, not open in the middle.

#5

You may not understand, but you solved my problem anyway!

I just needed to do the feeder tubes in two steps.

  1. Boolean subtract a cylinder to make the hole, then

  2. Add a cylinder pipe sitting on top of the hole.

As for flipping the inner face, I’ll work on that separately. Most likely user error.

I was pretty sure the meshes well constructed and were water tight, but that just means I was sure, not that they were so. But for the nonce, I havre something that works.

Thanks so much!

#6

Well, I’m glad your issue is solved at any rate!