Multi Color 3D Printing with AI

If you landed here, you're probably looking for a way to create multi-color 3D prints without tearing your hair out in complex CAD software. You've got a Bambu Lab AMS or a Prusa MMU, and you want to use it.

Most AI 3D generators spit out a single mesh. A blob. That's useless for multi-color printing unless you want to spend hours painting in the slicer.

GrandpaCAD is different. It supports multi-part object generation natively. As far as I know, it's the only AI tool doing this right now.

Seeing What You Made

When you ask the AI for a multi-part model, it can be hard to see if the parts actually fit together or if they are just mashed inside each other.

I added a specific tool for this. In the top right corner of the viewport, there is a button with this icon:

Pressing that toggles an "exploded view." It pulls the parts away from the center so you can inspect the geometry of each individual component. It's a lifesaver for checking internal structures or ensuring a lid actually has a lip to sit on.

How to Get Good Results

Generating multi-color models requires a slightly different approach to prompting than single-piece statues. Here is what I've found works best.

Ask for Multiple Parts explicitly

Don't just say "a red and blue box." Say "a box with a separate lid." The AI understands the concept of assembly. If you want different colors, you usually want different physical parts (unless you are doing very advanced multi-material single-mesh stuff, but let's stick to parts for now).

Use Colors for Clarity

Tell the AI to color the parts differently. "Make the base red and the letters white."

This doesn't just help the AI understand context; it helps you. When the model generates, you can instantly see which part is which. If everything is grey, good luck figuring out if that cylinder is a separate insert or just a bump on the surface.

The No-Overlap Rule

This is the big one. Slicers hate overlapping geometry in multi-part prints. It confuses the toolpath generation.

You need to be specific about fit. Tell the AI: "Ensure there are no overlaps between the parts."

If you are making parts that need to fit together (like a peg in a hole), ask for tolerances. "Make the hole 0.2mm larger than the peg for a loose fit." The AI is surprisingly good at math when you give it explicit constraints.

General Design Tips

Even with AI doing the heavy lifting, the physics of FDM printing haven't changed.

Flat bottoms matter. If you are printing a multi-colored sign or logo, try to design it so the color changes happen on the first few layers (face down) or as a distinct swap at a certain height. This will save you a lot of wasted filament.

Avoid impossible overhangs. If you have a white insert going into a black shell, make sure both parts can actually be printed without support material getting trapped inside the interface.

Think about assembly. Sometimes it's easier to print two parts separately and glue them than to print them in place with a purge tower wasting half your filament. But if you want that print-in-place magic, make sure you leave a gap. A 0.3mm gap is usually enough to break parts free after printing.

It's still early days for AI CAD, but being able to describe a multi-part assembly and get a ready-to-slice 3MF file is a game changer for those of us with multi-material printers.