Assuming you’ve followed the build instructions to the letter and purchased all of the recommended items and stuck the landing on the build too…
Plunging is difficult. Lead in from the side, Ramp, or Trochoidal milling only.
I’ve never used HSS bits in aluminum. Too many reasons to go into, but suffice it to say that Carbide and Ti coated carbide are the endmills to use. Start with a single flute if you can. Try 6061 aluminum. It machines far better than the big box store extruded stuff.
Al Machinability Quicky
I’ve only had luck with High Speed Machining tool paths in Aluminum. I remember sweating rather profusely while questioning my sanity running high feed rates I normally reserved for plywood.
Keep at it. Unfortunately, this isn’t a one size fits all effort.