This is known as the Push/Pull Scale and Rotate (PSR) method. From https://help.sketchup.com/en/sketchup-best-practices-and-applied-principles,
“The Push/Pull Scale and Rotate (PSR) method can be very helpful in modeling organic and complex forms. This method requires good judgement on the part of the modeler when determining the amount of accuracy. The Push Pull tool in combination with the Scale tool allows quick linear concentric modeling. This method works especially well when you have plan, section, and elevation drawings of the object.
Begin by drawing a profile shape. Then use successive push/ pull operations and scale and/or rotate on the new extruded profile. Notice that the center method was used for the scaling operation (Ctrl modifier [Option key on Mac])
Over the course of several of these iterations the object takes shape. The interior edges have been softened and smoothed with Ctrl-Erase [Option-Erase on Mac]
The profile can be modified at any stage by adding vertices and then adjusting the shape with the Move tool on a vertex. You can also vary the profile by changing the scaling points from center to corner or side. This allows the profile to change asymmetrically over the shape.
This method is not limited to concentric forms. Much more complex forms can be modeled from a tennis shoe to an automobile.”
Here’s an example of modeling a pen from existing CAD geometry using this method: https://www.youtube.com/watch?v=OSd-GnKQDAI
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