While developing the My Little Monster app, we gathered a substantial amount of information on color 3D printing. We wanted to share this with everyone. Enjoy.
Brief summary: Mineral powder or sandstone is the only material capable of full-color 3D prints. Produced on Z-Corp printers, models are created by printing binder material and colored ink layer-by-layer into a bed of gypsum-based powder. After printing, the models are finished with a cyanoacrylate (super glue) sealant to ensure durability and vivid colors. The final product is a hard, brittle material that works great for figurines.
Stratasys released their first color 3D printer early 2014. Object500 prints objects smooth like plastic with vibrant colors. Unfortunately, it’s about 7 times more expensive than Zcorp printers. It is designed for prototyping and professionals.
STEP 1: THE MODEL (using Autodesk Maya.)
Begin by setting your Maya units to millimeters: Window > Settings/Preferences > Preferences > Settings
Measuring is an integral part of modeling for 3D printing. You are going to continually use the distance tool to make sure that all of your items are big/thick enough to print. Measuring Tool: -Create > Measure Tools > Distance Tool.)
The minimum thickness that your model can be is 2mm. Anything thinner than that will be too brittle and break.
Your model needs to be watertight. (if you were to fill your model with water, would it leak?) Every surface in your model needs to be closed. Even if two objects overlap or intersect, they both have to be closed.
In addition, the face normals of the object need to point in the correct direction: outward of your object. When printing, the direction of the face normals determines what’s the ‘inside’ and ‘outside’ of your object.
Will it stand?
If your model is going to stand, like Monstermatic monsters, make sure the base (feet if he is standing) is flat and will support the entire model. Very fat characters on two very thin legs will probably snap and break.
If your model won’t stand on its own, you can add a base to your model. Again, make sure that the center of the mass is well inside the base area (ideally at the center) to make sure it won’t topple over. However, a base will require additional material so it’ll also raise the price of your object. Even a small base with a diameter of 5cm and a height of 2mm (minimum thickness required for color printing) gets expensive rather quickly.
The sandstone material is very delicate, so any embossed or engraved details must be at least 0.4mm. Anything less than that will not show up on the print. What is considered a detail? It’s kind of a grey area that is hard to describe, but the rule of thumb is usually anything that is twice as wide as it is tall.
STEP 2: THE TEXTURE
Just like in any ‘2D’ color printing process, printed colors may differ from the ones on your screen. Each pixel on your screen is composed of Red, Green and Blue colors (RGB), while full color sandstone printing uses Cyan, Magenta, Yellow and ‘Key’ (Black). The translation from one set of colors to the other will shift colors slightly, and makes some bright colors more subdued.
Tips to produce better colors:
•CMYK is best at producing bright, well defined colors. It’s best to have hard edges to your colors, limiting gradients and shading.
•Some colors are just hard to print: brown, brown tones, and flesh tones are difficult to produce and sometimes inconsistent because these colors require mixing all 4 inks (CMYK).
Small details will be lost in the printing.
Even though the resolution of the inkjet printhead is around 300DPI, the effective resolution of the transferred texture map is probably closer to 50DPI. Of course, it is all relative to size. Some details that will get lost on a 63.5mm model will show up nicely on a 152mm model.
C. Make sure all materials have a texture assigned to it. Materials without a texture file assigned to it will show up gray.(Even single colored materials)
STEP 3: THE SCALE
Maya units (in, cm, mm) don’t translate to real printable units. For our model, we had to scale down the mesh to 36% its size. (this percentage worked for us, it may be different for you)
STEP 4: THE EXPORT
ACCEPTED FORMATS FOR FULL COLOR 3D PRINTING:
.X3D, .X3DB, .X3DV, .WRL, .OBJ
NOTE: Maya exports .VRML2 (similar file type as a .WRL) but doesn’t export it correctly.
.OBJs are the best format to export from Maya. However, at this time, not all of the third-party 3D print companies accept .OBJ files.
Here is a way around this.
A. Select the mesh to print and export as an .obj (File > Export Selection…)
Default settings are fine
Save to an empty folder (This is important in keeping things organized)
Maya will spit out an .obj (the mesh), an .mtl (the material file), and it’s connected textures.
B. Open MeshLab (http://meshlab.sourceforge.net/)
C. Convert the .obj into an .x3d file (File > Export mesh as…).
D. Export as .x3d. (uncheck all of the boxes except for TexCoord under Wedge) Hit okay.
E.Export into the same folder that the .OBJ is in.
F. Grab .x3d file and all of its textures and create a zip folder. (DO NOT create a folder, throw files in folder, and create zip folder from that folder)