This is why patent drawings are an absolute must.
Involving shading techniques For preparing the patent illustrations, the illustrator often uses shading techniques.
Even though you can avoid using shading techniques for your patent drawings, it helps in improving the patent drawing quality.
Extensive use of rough sketchIf you think that the illustration is drawn at once, you may be wrong.
The patent examiners still use conventional methods and this required you to prepare your drawings in the conventional method.
However, there is no hard and fast rule about not incorporating any 3D model in your drawing.