Modules

At some point, things are going to get complex. You are going to have objects twisted around other objects, modifying other objects that are used in combination with yet more objects.

It helps then that openSCAD supports modules to organize stuff. Modules are simply a bunch of instructions that go together.

To illustrate how they work, let's make a funnel as shown in Figure 7.

Figure 7: A funnel built using modules.

A funnel is made up by two parts: a hollow, cut-off conical object that I am going to call the hat (I couldn't find formal names for the parts of a funnel, so I am improvising here), and a hollow cylinder I am calling the pipe.

Turns out both the hat and the pipe can be made entirely from cylinders, since the hat, for openSCAD, is a cylinder with two different diameters at each end. As you need it to be hollow, you make another cylinder with a slightly smaller radius at both ends and subtract that from the bigger one. The module for that would look like Listing 3.

module hat () {
  difference () {
    cylinder (r1=8, r2=2, h=10, center=true, $fn=50);
    cylinder (r1=7.5, r2=1.5, h=10, center=true, $fn=50);
  }
}

The pipe module is even simpler (Listing 4), but you do have to remember to translate the lower end of the pipe to the top of the hat (line 2).

01 module pipe () {
02   translate ([0,0,10]) {
03     difference () {
04       cylinder (r=2, h=10, center=true, $fn=50);
05       cylinder (r=1.5, h=10, center=true, $fn=50);
06     }
07   }
08 }

With these two modules, you can create a funnel () module that calls the other two (Listing 5, lines 17 to 20). Then call the funnel () module to actually show something in the preview pane (Listing 5, line 22).

01 module hat () {
02   difference () {
03     cylinder (r1=8, r2=2, h=10, center=true, $fn=50);
04     cylinder (r1=7.5, r2=1.5, h=10, center=true, $fn=50);
05   }
06 }
07
08 module pipe () {
09   translate ([0,0,10]) {
10     difference () {
11       cylinder (r=2, h=10, center=true, $fn=50);
12       cylinder (r=1.5, h=10, center=true, $fn=50);
13     }
14   }
15 }
16
17 module funnel () {
18   hat ();
19   pipe ();
20 }
21
22 funnel ();

You can take this modularity further and save a set of modules into a separate .scad file altogether. You can then import them back into other files using either the include or the use methods.

The include </path/to/file.scad> method imports the whole thing, modules and commands that are not in modules, integrating the whole imported file into your current file. The use </path/to/file.scad> method, on the other hand, only imports the modules so you can use them as library modules with the code in your current file.

This means that, to get a funnel with include, all you have to do is:

include <funnel.scad>;

To do the same with use, you would also have to call the funnel () method like this:

use <funnel.scad>;
funnel ();

Conclusion

This article has covered the most essential bits and pieces of the OpenSCAD language. With this and the user manual's excellent documentation [5], you should be able to start creating your first 3D pieces.

That said, there is quite a lot more to learn regarding OpenSCAD. We'll be looking at more advanced things in next month's issue. We will also be creating a real piece to print and showing how you can go all the way from concept to real physical object.

Until then, have fun!