Center Punch Tricks
Here's what my tool 'n die maker father and some experience have left with me:
The only reason a center punch dents, instead of making a nice pin-prick crater, is because you did not back up the material with some mass.
The caution of not using a center punch on aluminum is if you don't intend to drill it out. Think of all those pre-punched holes!; they're undersized so that drilling removes the stresses in the shear line. Center-punching does cause a bit of stress (it would on any material), but still can be used to identify parts and orientations on aluminum if you don't bludgeon the part to death. (These last two points are in the builder's manual, also.) Use a 2-ounce machinist hammer, gently.
The auto punches are a disaster waiting to happen. Since you have to apply pressure before they actuate, there's an increased possibility of skidding before they ding. And you can't control the force without fiddling with adjustments. It's far easier to position and control a sharp, fine point punch tapped with a light hammer. Also, you can walk a slightly mis-aimed punch across the surface by tipping the punch.
The secret: massive backup behind a well restrained or clamped part.
John Siebold