Router bit bumpers with dried silicone obviously works for the bottoming out problem with router bits. An easier solution with no mess or fuss is to simply roll a small “O” ring onto the shaft. O rings from old water shut-off valves work great for 1/4″ shafts. Half inch shafts need a larger ring but they are not hard to collect. I save mine from water filters from my KitchenAid® refrigerator.
Halfmoon Bay, BC, Canada