IMPORTANT LEARNING: Drill pilot holes just under 1/4" before using router bits (same size or slightly smaller than twist drill shank). I used 1/8" pilot holes and one bit broke as soon as it hit the metal. I drilled a larger pilot hole and the broken bit still centered the router for a good hole. Using 18 gauge mild steel and a 2 -inch slot, there was no problem like the others when drilling large pilot holes.