The ability to make freehand drawings is space is probably the most celebrated feature of the 3D printing pen. It is also the most difficult. Making drawings in empty space is extremely difficult. You will need to practice quite a lot before you can make nice shapes like the ones that you see in the advertisements. So don't be discouraged if your first attempts don't look very good.

To begin a 3D sketch, you need to start with a solid anchor point. Make a large dot of plastic on the paper. Then slowly lift the pen into the air while extruding at the slow speed. You need to move your hand at the same speed that the extruder pushes out the plastic.

To make a straight line, hold the body of the pen in line with the plastic and very gently pull on it. A small amount of tension will keep the line of plastic straight while it cools. When you reach the point where you want the line to end, stop extruding plastic and hold the pen still for a few seconds. The plastic needs to cool and resolidify before it can support its own weight. You can help the plastic to cool more quickly by gently blowing on it or by having a small fan pointed at your work area. Once the plastic has hardened, pull the pen away. The melted plastic in the nozzle may leave a small point or trail off in a string from the pen. You can just trim this off with scissors or wire cutters.

Making a curved line is more difficult. Again, start by making a thick bead on the paper to use as an anchor point. Lift up the pen from the paper while extruding at the slow speed setting. Move the pen in the direction that you want the plastic to initially go as if you were making a straight line. Once you have extruded about an inch of plastic, stop. As the plastic begins to cool you need to move it into the appropriate shape. You can speed up the cooling process by gently blowing on the plastic or by having a small fan pointed at your work space. Once the first bit of plastic has been worked into the appropriate shape, extrude another inch and shape that section. Continue this process until you have completed a large section. You will eventually need to create another anchor point because there is only so weight that one point can support.

When you want to join two pieces of plastic, hold the pen at the junction for a few seconds. This will allow the heat from the tip to partially remelt the first piece and fuse the two sections of plastic together.

The most difficult part of creating freehand sketches in space is working at the right speed. You need to move your hand at the same speed that the extruder puts out the plastic. Otherwise it will sag. You have to move the pen around to shape the plastic as it is cooling. So you need to intuitively know how quickly the plastic will cool and solidify. This takes a lot practice to get down.