This is part of the series of 30 exercises developed during the 3D4KIDS program. One of the aims of this Erasmus+ program is to improve the knowledge of teachers regarding the 3d printing technology by developing some specific training materials. More info in the website: https://www.3d4kids.eu/ This activity is about drawing in diedric system intersections of solids (cylinders, prisms, cones, cubes, pyramids, tetrahedrons…) with planes in different angles. Students will have to draw the diedric projections of a solid intersected by a plane with a certain angle α. After the teacher explanation of the activity, students will use the 3D printed solids cut in two pieces, according to the intersection of the plane with a certain angle. Then, they will be able to see the resultant shape of the section in the solid.