Join Ryan Kittleson for an in-depth discussion in this video Splitting up a model that is too big for a 3D printer, part of ZBrush: Tips & Tricks.
- I often need to print things large, but 3D printers have a limited build volume. In times like these I have to cut up models into smaller pieces so they can be printed and put back together afterwards. Let's see some techniques for that. So I've got my bull model here, and let's just see how big it is. Go into our move transpose line here. Let's look at it from a side view. Just draw out a new line, and you can see it's roughly seven inches long. But let's say that the printer we're printing on can only print up to five inches, like a cube of five inches on each side.
Now of course every 3D printer has a different build volume, but just for the sake of argument, let's say a cube of five inches is our maximum volume. So what I like to do in cases like this is to get a cube or a rectangular box into my scene and compare it with the model. So let's go into Sub Tool and let's go to Append to make a cube 3D, let's select it to make it active, and now we can come down to Geometry and take a look at its size. So by default, objects in ZBrush are two units, so let's go ahead and change this to five.
And if you need to change any of these dimensions feel free to set them to whatever is right for your printer, but five, five, five is good for me. Okay, so you can clearly see there's no way this bull is fitting into this print volume. So we're going to have to cut it in half. For this, let's go ahead and go back to our bull. We can hide that box for right now. Okay, now let's split the bull into two separate polygroups. So for this, let's get the slice rectangle brush. I'm going to hold down Control + Shift to get the select brushes that are used with that key combination, and let's go ahead and click on that and go to slice rectangle.
Okay, now with this active, what we can do is just click and drag over the bull, and just cut it anywhere in the middle. It doesn't have to be precisely any particular location. I usually just like to put those lines in places that have less detail, just so it's not going to get in the way of any particular shape, but since the middle section of the bull is relatively less detailed than the rest of it, that's a good place to put it. Okay, let's hit Shift + F to turn on wire frame and see what that did. Okay, great, so we've got two different polygroups here.
Okay, so now what we can do is split this into two. So let's go to Split and Groups Split. And this is okay. It's just letting us know it can't undo this. Alright great, so we've got this cut into two. Let's go ahead and hide one of these for right now. And now what we can do is just close this hole. So let's go into Geometry, Modify Topology, and Close Holes. Now this usually works pretty easy, pretty fast. Every once in a while you'll run into a problem where there's kind of a concave shape right here, where this close hole will fill in kind of a web across something like that.
So if that happens you might want to use the ZModeler brush, so I'll use the ZModeler brush on the next one. So let's switch to the first piece and we'll hide the one we just worked on. And now let's hit B + Z + M on the keyboard to get the ZModeler brush. That's okay, we can skip this note. And now let's zoom in really close here on one of these edges. Okay, and we can hover over an edge, hold down Spacebar, and let's go into Close mode.
And I'll just click on an edge. Now this algorithm that closes the holes through the ZModeler brush is a little bit more precise than the Close Holes though the Geometry sub-palette. So if you run into problems with the Close Holes through Geometry sub-palette, then go ahead and use the ZModeler brush. Usually if the concave shape isn't too pronounced, the Close Holes button does just fine, but if you run into a problem, the ZModeler brush is always there. Okay, let's see how these individual pieces fit inside the box.
Go back to our Move modifier here, and let's go into our SubTools, let's bring back the visibility on that box. We'll go into transparent mode so we can see the bull through the box, and you can see if we move the bull it definitely fits inside the box. And let's make sure this other piece goes in nicely as well. Alright, looks good. Now you can keep splitting as many times as you need to until all your parts fit nicely into the volume box.
But remember that most 3D printers require a little extra space for something called raft, which is kind of a foundation for the print, and also support structures. So don't try to make the pieces fill up exactly to the bounding box. Make sure your pieces are a little bit smaller than the maximum volume so that you have a little bit of room for those extra things. Okay, from here you would export these for 3D printing like any other time exporting for 3D printing, but I'll let you take it from here with that 'cause that goes into the whole 3D printing export, and that's a different thing.
But hopefully now you see how easy splitting up a model into smaller pieces can be.