APPENDIX B ■ APPENDIX B
Designing the Model
The first step in 3D printing is to create or obtain a 3D model. Think of this like making a document
on a word processor before printing it to a 2D printer. Figure B-5 shows the model of the Lego motor
coupler, which took about 30 minutes to design. You can download the printable file from
http://www.robotroom.com/SandwichStuff.html.
The model has a slot for the Lego cross axle, a hole for the set screw, a hole for the motor shaft, and
a small flat area inside that hole for the flat part of the motor shaft. Both the motor shaft and set screw
holes are slightly countersunk to make insertion easier. These features would require extra steps during
conventional machining, but do not significantly affect print time with 3D printers.
I made the coupler model using a free online tool called Tinkercad. Not surprisingly, there are plenty of
competitors, each with advantages and disadvantages. The advantage of Tinkercad is that it is free and easy
to learn. The disadvantage is that the model files are stored online only, and you should always be wary of
how long free tools (and your files) will be supported and available.
Adding and Subtracting
There are a variety of ways to design a 3D model. Artists and sculptors often require different techniques
than do engineers. For example, a 3D game model needs to be designed for computing performance and
aesthetics, whereas a robot part needs to be designed for fit and function.
For beginners, an easy to learn 3D technique is called constructive solid geometry. Put simply, you
place a primitive shape, such as a cube, sphere, or cylinder, and then you either add or subtract another
primitive shape. For example, take a cylinder and subtract a smaller cylinder to create a tube. See Figure B-6.
Figure B-5. A 3D model for a Lego cross-axle coupler designed in a CAD application