I believe the OPs Ryobi has a 1/4" collet. At least all that I've seen. As for a 11/2" bit w/1/4" Shank is asking for problems. These are not sturdy routers to begin with. I've had one for years. I don't use it as much as my smaller routers.You can purchase a longer bit. I took a quick look at the MLCS catalog and they have a straight bit with a .5" shank that is 1.25" long. I'm just a hobby woodworker and don't have a lot of router experience but it seems like lot of material you trying to remove. I think I get a longer bit and try doing it in a couple of passes. I'm sure someone with have a better plan.