Another trick I have used is to take a piece of round bar stock (1/2" or 3/4") and grind a radius in the end that is slightly smaller than the radius of the curves in the grill. Clamp the bar in the vise and rest the grill bar on the radiused end of the bar and hammer it on the outside. Be careful not to beat on it too much or the metal stretches. This even works on things like dust caps for the front spindles or anything with a tight radius bend.