Chapter 6: Boolean Operators

Anheben

So we now know a couple of tools for 3D construction within ACAD. In this exercise, we want to take a closer look at all the tools, that we did not touch so far. We will try to build our column another way this time. We again start with attaching the topview of a column and as a reference take the reference file. As discussed in Chapter 2, we'll do a redrawing of the column on another layer as a start. If you want, you can also use the other shape on the right side.

Instead of creating individual barrels by extrusion, we will this time create a one piece column, that will get a bit thinner on top. For that, we will change to 3D view and copy our redrawing exactly on top of the original one, but at a height, that seems reasonable for us. We then want to scale the upper shape a bit smaller, in order to have a column that gets thinner on top. Select your shape and use the Skalieren/Scale tool of the Start menu. ACAD wants to know the base point for scaling. If you enter 0,0,0 in the command line, you'll have a good point of reference. If you move your mouse up and down, the scaled shape should move into view. As you can see, the closer you get to the absolute zero point, the smaller the shape gets. Try to scale the shape just a little bit down, not too much.

We can now try to connect these two shapes by the use of a new tool called Anheben. Select the tool from the 3D-Werkzeuge menu and then click the bottom and after that the top shape and press Enter twice. You should see a result like on the screenshot on the side. Actually we are not done yet, so press CTRL+Z to undo your result, so that you again see only the two shapes on top of each other. We want to use the tool now to not only create the shaft of the column, but also the Echinus. To do that, we need one copy and a couple of cirlces.

First of all, make a copy of the upper shape and place it slightly above the original one. Then change in to top view and create a simple circle that is slightly larger in diameter then the Doric Column shape. This will be our Echinus base and should be placed also equally slightly on top of the last shape. For better understanding: The red lines are the Doric shapes and the blue lines are the circles. We now want to copy the first circle, move it up and make it slightly larger. We repeat that step one more time, to get the maximum diameter of the Echinus. The next copy should also be placed slightly on top but scaled a bit down again. The last circle, should simple be a copy of the first circle and placed on top.

Try to redo now the Anheben tool, but this time select all the shapes from bottom to the top in that order and press Enter two times. Isn't that nice? If you take a closer look, you can clearly see the transistion between the Doric shape and the circle shape, which is nice and smooth. This tool is great for something like that, where you want to get a more dynamic result. Basically, you only have to put a cube on top as an Abacus and you are done.

Boolean tools

We also want to have a closer look on the Boolean Tools. Boolean Tools basically mean modelling with boolean operators: AND, OR, NOT. These operators are used within mathematics, but we can also use them with 3D modelling. In AutoCAD these operators are called Intersect (AND), Union (OR) and Subtract (NOT).

Let's have a look at them. If you create a box and on each of the upper four corners a sphere, we can experiment with the Union and Subtract tool. Select the Union tool from the 3D Tools menu. Remember, if you do not have the 3D tools visible, you have to turn them on first. Also remember: The shortcut for 3D snapping in AutoCAD is the F4 key. Try to build the spheres in a way, that their centre point is exactly at the corner of the box. After selecting the tool, you can select the objects you want to union (or combine). So select two of the spheres plus the box and hit Enter.

It doesn't look like much, but if you hover with your mouse over the object, you'll see that the box and two of the spheres are now just one object. So, now let's try something else. Select the Subtract tool and then first the box (with the two connected spheres) and hit enter and then one of the remaining loose spheres and hit enter. You can repeat the process for the other remaining sphere and your result should look something like this.

So far for the Union and Subtract tool. In the following example, we want to take a look at the third Boolean Tool of AutoCAD.

Create a sphere and a cube. I want you to stick the cube into the sphere like in the screenshot on the side. So the cube should stick inside of the sphere with one of its corners. Then select the Intersect tool and then both objects and hit enter. You are left with only the part of both objects that did intersect. Great no? If you are a perfectionist, try to construct a combination of sphere and cube, where the corner of the cube is exactly in the centre of the sphere...

Now these tools offer us a great opportunity to up our modelling game. Sometimes it makes sense to combine tools and sometimes it doesn't. In any case, modelling (or rather sketching) in 3D can have some valuable use-cases. I already said it and will say it again: AutoCAD is not the best 3D software out there, but it can be certainly used to sketch things in 3D or to visualise what you already have done in AutoCAD anyway. To deepen our knowledge of the 3D modelling tools of AutoCAD, there is only one last challenge: try to rebuild the objects down below and have fun!