For aluminum or fiberglass don't use a standard router bit but a 3-flute carbide end mill. (Link below) The carbide lasts a long time and the 3 up-cut flutes clear out the chips. My machinist son put me on to these a couple of years ago and they work great. They work especially well on fiberglass. Only problem I have I the solid carbide shank is hard to grip in the router chuck. I scuff up the shiny shank just a bit with on my diamond whet stone and they stay put.