In Blender, you can use many tools to shape a model as much as you want. You also have some aids when modeling based on a 2D drawing. However, did you know you can have a 3D guide in Blender? Well then, how to use the Knife project Tool.
The Knife Project Tool is not like the Knife or Bisect tool; it takes open edges of one object and uses them to make cuts into another primitive.
But first, let’s be clear: an open edge, also known as a wire edge, isn’t attached to anything around; you can see it on a flat surface like a plane or a text object. In contrast, the common meshes, like cubes, spheres, cylinders, and so on, are Manifold Objects, which means that every edge in the figure is connected to another face.
Therefore, the Knife project Tool only works from an object with a wire edge because this is the guide to shape the other figure; and how it will transform the manifold will depend on the perspective and the view angle you’ll be at the moment to make the operation. To enable this tool, you only need to follow the steps below:
Then you can look at what you just did with the tool. Now the model you chose has cut points, edges, and drawn faces directly where you located the wire edge object. Hereafter you can do whatever you want with the new faces and shapes created, like extruding, deleting, etc.
Note: Remember that you can do this process even from a funky angle in Perspective view.
However, you can also hit number five (5) to go to the Side Orthographic View, which will help you to modify your object straighter.
And finally, if you want to add a wire edge figure, you can press Shift + A to bring up the Add Menu, select the “Circle”, and in the pop-up in the left bottom corner, change the values of vertices, radius, etc:
There you have it. You can add and transform tour meshes in almost any way you can imagine. Good Luck!