Tuesday, March 6, 2018

ITEC's Jerry Brown on Modeling for 3D Printing Best Practices

By Jerry Brown, Director of Media

More on Jerry Brown can be found here.

At ITEC Entertainment we often have the need to produce physical models of props, buildings, ride cars and more to tangibly visualize 3D models or prototype an item. 

Unlike 3D modeling for film or video, your models don't just have to look good, they need to be built a certain way so they can be physically 'replicated' in the real world with real world physics. Here are my 10 tips and best practice recommendations for when modeling items for 3D printing.

Tip #1: Models must be watertight with no holes. If the object you are creating is designed to have a hole (like a piggy bank), it must have an outside and an inside and have a defined thickness. The entire area must be closed watertight and void of missing polygons and/or unconnected polygons.

Tip #2: The object must be what is referred to as manifold – meaning that one edge of the object cannot share more than two faces. This sometimes occurs during modeling when extruding edges vs faces, OR when extruding faces inwards but not up or down. This causes a shared edge among several polygons. 3D printers don’t know how to interpret what is to be done with those. 

Tip #3: Normals must be oriented in the correct (outward) position. In the piggy bank example – the outside edge normal must face OUT, and the inside surface normal must face IN.

Tip #4: Don’t make detail too thin. Everything must have a thickness that is more than 2 to 4 millimeters. Some printers will not print very fine detail, especially if the detail is unsupported or sticking up by itself. For best results, avoid antennae, hair, strings, or wires, and other unsupported detail in your models. 

Tip #5: It is good practice not to overlap or intersect geometry. Instead, try to connect (Boolean) them. For example, if a gun barrel is sticking out of a tank top turret, try to connect the gun to the tank top instead of just placing it through. 3D Printers sometimes get confused on what object is printing (the gun or the turret), and will sometimes build up plastic in that one area. Keep this practice to a minimum and you will have better 3D print results. 

Tip #6: Be aware of overhangs. Most 3D printers print like an ink jet printer (one layer at a time on top of the previous layer). Overhangs will require the printer to make a ‘support’ which is built into most slicing software which is helpful to take into consideration when modeling. Most 3D printers can print a 45 degree angle without support and can also print spheres without the need for additional support structure. 

Tip #7: Consider modeling something in two or more pieces that can be glued or connected together after printing. This will help you avoid having to use supports. For example, a ship's hull can be printed in 2 pieces and then glued together. Or in the example below, this chess piece would have needed supports to print the top. By separating the piece at printing stage, and gluing the pieces together later, you will avoid the need for supports. 

Tip #8: 3D printers only print the data that is displayed as polygons. They do not print bump, normal, or displacement maps. If you create something using a third-party 3D sculpting and painting tool like Mudbox or ZBrush, you will need to convert to polygons first. Some modeling software like Maya has a mode called Smooth Mesh Preview, which will show how it will "render" but it will print without the smooth mesh preview and use the polygons.

Tip #9: Try to keep your polygon count to a reasonable level. The more polygons, the heavier the print increasing the chances of a software crash. 

Tip #10: Consider size restrictions. Most consumer desktop 3D printers can print an object at approx 6x6x6 inches, some a little larger, some a little smaller. Keep this in mind when creating a model. If you create a 10 inch action figure, you will find that very few desktop printers will print that size at the moment. If you need to print a larger item, consider splitting it up into several pieces and assembling after. NOTE - this is also a good idea for prints that take a very long time (over 10 hours) to print. Better to cut these up into smaller, two hour prints. There is nothing more frustrating than a fifteen hour print crashing in the fourteenth hour because of power failure, etc, and having to start all over!