We have a bit about endmills at:
Please note that most drill bits aren’t suited to use at the speeds at which trim routers/spindles spin — you’ll want to use an up-cut endmill for metal for chip clearance (straight is okay if the pockets aren’t too deep).
Usually you use a slightly smaller endmill and machine as a pocket — ideally leaving a roughing clearance and taking a finishing pass — that avoids a lot of potential problems. See: Adding geometry to cut as a pocket with a finishing pass