I removed a hub yesterday using my home-made hub puller, and it was so tight that it took over an hour to get it off. However, after getting it off, it went right back on very smoothly. If you can't get the hub back on without beating on it, you have some other problem. As has been said, be sure that the axle is rust-free, clean and no burrs on the key slot. Be sure to clean the inside of the hub as well. Try sliding it on without the woodruff key. Does it go on easily? If so, the problem may be the key. Once you get the hub to slide on the axle and key easily, coat the axle with a good anti-seize compound before attaching the hub with the set screw.