I build firetrucks for a living. We holesaw stainless everyday all day. Buy good quality hole saws. We use Makita and Milwaukee. Don't even try to do your visor by hand . You will ruin both the saw and the visor. A drill press with a firm holddown would suit your project best.Back up your work with a wood block to keep from damaging the drill table. A 3" saw is rated to turn at 165 RPM, no faster. Slower is all right. While water will cool the saw it does nothing for lubrication and that is very inportant for saw life. Use a water soluable cutting oil and use it freely. Feed just fast enough to keep the saw cutting but not fast enough to stall the saw. Satinless will work harden almost instantly if you let the saw stop cutting. Figure about 3 holes to the saw in 18 gauge.