3D Printing with ZBrush
Illustration by John Hersey

Cutting a hole in the model


3D Printing with ZBrush

with Ryan Kittleson

Video: Cutting a hole in the model

In order for a model to be hollow, there has to be And we'll just draw in the rest of the mask to fill in this area.

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Watch the Online Video Course 3D Printing with ZBrush
1h 14m Intermediate May 30, 2014

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Prepare your models for 3D printing with ZBrush, the popular program for 3D modeling and digital sculpting. Learn how to measure your models with real world units, so everything prints at the right size; save on material costs by hollowing out your models; and make sure your colors print true. Author/artist/3D aficionado Ryan Kittleson also shares some advanced tips and tricks for getting the best results from your particular printer.

This course was created by Ryan Kittleson. We're honored to host this training in our library.

Topics include:
  • Combining multiple objects
  • Sizing an object with real-world units
  • Fixing parts that are too thin
  • Cutting models into smaller pieces
  • Making models hollow
  • Working with color 3D prints
3D + Animation
Ryan Kittleson

Cutting a hole in the model

In order for a model to be hollow, there has to be an opening for the unused material to come out from the inside. Let's see how to cut a hole in the model. Now, there's a bit of prep work to do before creating the hole. I have my model in one, single sub-tool. However, each of these pieces, like the hair, the head, the jacket, are all separate objects. It's going to be easier to work on them if I break them into separate sub-tools. If your model is all one conjoined surface, that's fine too, you can leave it the way it is.

But I'm going to go to split under the sub tool menu and go to split to similar parts. Okay, so now I've got a separate sub tool for each of the parts of the model. Next thing you want to do is identify if your surfaces are open or closed. So, for example, we can see that this model is all closed surfaces, there's no open edges. So we need to cut some open edges into it. I've got the jacket object selected. And what I want to do is cut a hole in the base. So, I'm going to go ahead and make my brush size a little bit bigger by holding down the right bracket key, just getting a bigger brush here.

And let's hold down control. And let's draw a mask here on the base. It doesn't have to extremely pretty. Just something to give us a nice opening here. And we'll just draw in the rest of the mask to fill in this area. Okay now let's get this cut out. So for this I'm going to go to geometry and we're going to go to edge loop, and edge loop mask border. So that's going to just neaten up the border of that selected area. And now let's delete this area. This also makes a new poly group where the masked area was. So what I can do is Ctrl+Shift+click on this and then Ctrl+Shift+click one more time to invert that selection, and now I can delete the hidden part.

To do that let's go to the geometry palette, and we'll go to Modify Topology, and Del Hidden. Okay, so that puts a nice clean hole in the model. Let's do this one more time for the head. You can see now we've only got an opening for the jacket, we need to make a hole in the head as well so material can go all the way through. So I'm going to Alt+click on the head sub tool. And now we need to select all the polygons here. We need to max these off. All the ones that are inside the jacket. let's make it easier to see this. Let's go to transform and let's turn on transparency mode.

This is going to make everything that is not the current subtool transparent. So now I can mask off everything that's on the head that's inside the jacket. Okay, let's go through that process again. Let's go to Geometry > EdgeLoop > EdgeLoop Masked Border. Ctrl+Shift-click on the mask. Ctrl+Shift-click on it one more time to invert that selection. Then go to modify topology under geometry, and Del hidden. Okay let's go back up to transform and turn off the transparency mode.

Okay, so you can see we now have a hole that's going through the jacket, and then into the head. Go ahead and repeat these steps, until you've got a hole through the head, into the hair. And a hole in the hair, as well. Don't worry about the eyes, or the eyebrows, or the teeth. These objects are too small to make a difference if you try to make' em hollow. So your model might already have an open surface. Depending on how you made it, there might be an opening already and if so, you don't have to worry about this stuff. There is only one other concern you might have, and that is the hole might need to be a certain minimum size.

If you look on the Shapeways website, you can see that different materials have a different minimum hole size. So you might want to go into your transpose tool and measure the size of that hole to make sure it's big enough. You'll see our hole is about almost 7 units across. So just make sure there's hole going all the way through the model. And that it's big enough to let out the material that's on the inside.

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