Back at the day, engineers could make complicated technical drawings hand, they will have Computer Aided Design (CAD) software. CAD software is based on different contours. You start by drawing a technical 2-d shape of your own thing, then it is extruded and modifications can be achieved, including holes, threads and snaps. The AutoCAD alternative allows for more precise design. Because it's based on a specialized sketch of one's object, every thing has to be quantified and accurate. https://www.alcads.com/