What type of sander should be used for concave (inside) curves?

The Drum/Oscillating Spindle Sander is specifically designed for sanding curved edges and concave surfaces. Its unique design allows the spindle to rotate while also moving in an oscillating motion, which helps to effectively sand the inner curves without damaging the surrounding material. This capability makes it ideal for achieving smooth finishes on intricate shapes that would be challenging to sand with other tools.

In contrast, other types of sanders, like the Disc and Belt Sander, are generally better suited for flat surfaces or convex curves due to their flat sanding surfaces. A Surface Sander is also primarily intended for smoothing out large, flat areas, while the Orbital Sander is designed for general sanding tasks on flat surfaces and may not provide the precision needed for concave curves.