Engineering Gadgets on Instagram: "For effective metal tube bending without damage, the best machine is a mandrel bender because it uses an internal support tool to prevent the tube from collapsing, wrinkling, or deforming. For large-radius bends where high precision is not required, a roll bender is another effective option."

Expandable Mandrels: Tool for Grinding, Turning, and Milling

Pile Driving Part II: Pile Types and Guidelines - Pile Buck Magazine