A roll bender is a big machine that helps people make metal things that are curved. It works like a big pasta roller that you might use in the kitchen, but instead of making noodles, it helps you bend metal things into different shapes.
You put a long skinny piece of metal in between three big rollers on the machine. Then you turn a handle or push a button so the rollers start to turn. As the metal goes through the rollers, it bends and turns into the shape you want it to be.
Roll benders are really helpful for making things like pipes or tubes that need to be curved in a certain way. They can also be used to make things like chairs or table legs that have a curved design.
Roll benders are big and heavy machines, so you have to be careful when using them. A grown-up who knows how to use the machine safely has to help you. But with a roll bender, you can make all sorts of cool things out of metal!