How to Break Your SketchUp Model into Parts for 3D Printing
As you do more 3D printing with SketchUp, you’ll run into the need to split your model into parts. Some ideas are just too big to fit into your 3D printer’s build volume. Other ideas want to be 3D printed in a rainbow of colored plastic. And sometimes a model just needs to be split to make it easy to print.
Where to cut your SketchUp model
When subdividing a SketchUp model into printable parts, start by thinking about what you’re going to do with the seams. If you’re going to sand, paint, and finish the model, then have at it and cut wherever you want. But sanding and finishing is a huge amount of work, especially if you’ve never done it before. It’s much easier to make your cuts and seams look like they’re intentional parts of the model.
For a seam to look intentional, it has to work with the logic of the object. Every object has its own logic, an underlying order that informs how it’s shaped and structured. For example, the object is symmetrical left and right. A seam on the axis of symmetry is less objectionable than one that runs randomly in another direction. By following a line that’s already conceptually present in the object, the seam reinforces what the eye already perceives.
Another good place to hide a cut is at a change in elevation, curvature, or color. Placing a seam where the surface of a part is already interrupted or in transition will make it far less noticeable. This is the strategy most commonly employed for injection-molding parts.
Pick up something around you that’s made of plastic and find the seams where the parts come together. If you can imitate that type of seam, people will readily accept that your object is a “real” thing. It will feel correct among manufactured things in our injection-molded world, and you’ll fool people into thinking your 3D printed part came from a factory somewhere.
For very large constructions, the only option may be to establish a grid and cut into build-volume-size blocks. Sanding, finishing, and painting can work well on large parts, but expect to spend substantial time doing it right. If you’ve spent the energy to build something that big, it’s worth the extra time to make it amazing.
How to cut your SketchUp model
Cutting a model into parts is very similar to using the Intersect Faces tool to combine groups. You use a piece of geometry as a cutter that will be intersected with the larger object and become the new edges of the cut.
If your model is fairly simple and you have SketchUp Pro, you can use the Solid Tools to short-circuit this process. Create a solid block as a cutting object and use the Solid Tools → Trim command. Remember to run CleanUp3 and Solid Inspector2 on the new parts when you’re done. For more complex models, or users with SketchUp Make, use the Intersect Faces method:
- Select the group you want to cut and make a new group around it.
The original group becomes a subgroup.
- Working inside the new group, create geometry in the shape of the cut you want to make.
Work on top of the subgroup, so you place the cut correctly.
- When you’re done placing cuts, make the new geometry into its own group.
- Select the Cutter object and choose Edit → Intersect Faces with Context (or choose Edit from the context-click menu).
Doing so draws a line at every place where groups touch. These new lines of intersection exist outside the subgroups and aren’t stuck to anything yet.
- Inside each group, use Explode to stick the intersection lines, cutting object, and base object together.
The surface of the cutting object becomes the sides of the new part.
- Move back out to the master group and make as many copies of that group as the number of parts you’re dividing it into.
- In each copy, open the group for editing and erase everything you don’t need in that part. Do the same in the other parts.
Just make sure you don’t erase what the object needs to do its job.
- Run CleanUp3on the new parts and use Solid Inspector2 to check for any accidental holes.
- Position the parts back together to make sure everything lines up as expected.