3D Designer

Language Basics

Here too the basics are, well, basic:

cube (5);

prints a cube with sides measuring 5 units. In my case, that translates to millimeters when I send it to my printer. The cube's lower left-hand corner on its front face is at the [0, 0, 0] position (Figure 1 again), so the cube is drawn to the right, up, and back from the viewer's initial point of view.

Although this is the default, you can add another parameter to the cube as follows:

cube (5, center = true);

to make the center of the cube coincide with [0, 0, 0], and then the cube is drawn around its central reference point.

You can also create in a similar way spheres, cylinders, and polyhedrons, the latter being customized 3D shapes.

To make the object appear in the preview pane, press the render button in the toolbar at the top of the script editor pane (second from right), or in the toolbar under the preview pane (second from left). You can also hit the F6 key.

You can move things around with the translate () function and rotate them with the rotate() function. To make this work, you embed the shape you want to modify within the function that modifies it. Listing 1 shows several ways you can do that.

  • In Method 1, you simply put all the commands on one line, with the inner-most nested element last and moving outwards as you move backwards to the beginning of the line.
  • Method 2 is a bit clearer, as it uses a notation similar to JavaScript or C/C++, where you user braces ({}) to enclose nested blocks of code. As we are on the topic of C/C++, notice how the OpenSCAD's language uses C/C++ style comments, with // to indicate a line comment and /* ... */ for multiple lines of comments.
  • Method 3 is similar to Python, as you use indentation at the beginning of the line to indicate which block of code is nested within which container.

In our example, you may be tempted to think that there is some sort of invisible 3D cursor at work. When you write

translate ([x, y, z])

it moves said cursor to coordinate x, y, and z. Then, when the renderer executes

rotate ([a, b, c])

it rotates the cursor in 3D space and then draws the cube.

However, that is not what happens. In fact, the renderer executes commands inner-most first and moves out from there. Think of it like this: The renderer first locates the object it has to actually draw. The operation nearest to the object gets applied first, then the next to nearest, and so on, until all operations have modified the object. In the example above, that would be the rotation is applied first and then the translation.

This is important, because the order in which modifications are applied to a body matter. In fact,

translate ([5, 5, 5]) rotate([45, 45, 45]) cube (5);

will give you a quite different result to:

rotate([45, 45, 45]) translate ([5, 5, 5]) cube (5);

Figure 2 shows both. The green cube shows what happens when you rotate first and then translate, and the red cube shows what happens when you translate and then rotate. They are in different positions because with the green cube, you rotate the cube while it is still located at [0, 0, 0] and then move it to where you want it to be (which is what you probably wanted to do all along). With the red cube, you move the object and then rotate, but the rotation takes the original point as its reference, so it moves the cube on a 45 degree arc measuring 5, with its origin at [0, 0, 0].

Figure 2: The order in which you apply modifiers to your objects can change where they are located.

Adding and Subtracting

There are several ways of creating complex parts in OpenSCAD. One of them is by adding, intersecting, and subtracting one object from another. Listing 2 shows a cube that has had a sphere subtracted from it (Figure 3).

Listing 2

Cube Minus Sphere

difference () {
  cube (10, center = true);
  sphere (6.5, center = true);
}
Figure 3: A cube that has had a sphere subtracted from it.

The way this works is that the second object (sphere ()) is subtracted from the first (cube ()). Notice that, due to OpenSCAD's scripting nature, objects never "go away" when you operate on them. In fact, you can still show subtracted pieces by typing a # in front of them and then hitting Preview (the F5 key). The "ghost" objects will show up as a translucent piece in the display pane (Figure 4).

Figure 4: You can show subtracted pieces as translucent bodies by using the # in front of the commands that create them.

Another way of showing all the bodies that make up a piece is by marking the checkbox at View | Thrown together in the menu.

The other two Boolean operations available are intersection (), in which you are left with an object that shares the space common to the two original objects (Figure 5), and union (), which just melds both objects together.

Figure 5: A cube intersected by a sphere leaves the space that both objects share.

Special Variables

You will notice that the sphere in the example above is looking a bit chunky. There are several inbuilt variables that can help with that. $fn, for example, sets the number of subdivisions in a curve. Use it like this

sphere (6.5, $fn=25);

to create a sphere with 25 subdivisions on each of its parallels.

In Figure 6, you can see what three spheres look like with, from left to right, the $fn variable set to 5, 25, and 50. The "sphere" (to call it something) on the left has north and south poles and an equator made from pentagons. Meanwhile, the sphere with a $fn of 50 looks much more sphere-like.

Figure 6: Use the $fn variable to make curved surfaces smoother.

You may be tempted to make $fn equal to 500 or 1000 to get a perfectly smooth sphere. Don't do that. Anything over 100 will eat up cycles from your CPU like candy, probably crashing your system. Besides, you are producing objects to print on a 3D printer. You'd need a crazily precise printer to be able to distinguish between a sphere with a $fn of 50 and another with a $fn of 500.

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