The Bonded Grinding Wheel
Bonded wheels are aggressive. They are designed for one thing: removing metal quickly.
Pros: High material removal rate, cheaper per unit, durable.
Cons: Leaves a rough finish, high vibration, can gouge the workpiece.
The Flap Disc
Flap discs consist of overlapping pieces of coated abrasive (sandpaper) glued to a backing plate. They grind and finish in a single step.
Pros: Smoother finish, less vibration, cooler cutting, lower risk of gouging.
Cons: Higher cost per unit, slower material removal on heavy stock.
The Verdict
Use a bonded wheel when you need to remove heavy welds or bevel thick steel plates. Switch to a flap disc when you need to blend a weld into the surrounding metal smoothly before painting or polishing.