I started reading a series of at least 7 books in the late 1970's. I only had books 1,2,4 and 7 - got them at a used book store at the time, so they may have been written in the 50's or 60's as well. I remember the series starting out on earth, with the main character learning sword play from a master. I remember there being some move he learned that was unbeatable. At some point I believe he discovers a portal to another world through a trap door. His skill with a sword is important to his success on this new world. That's about all I can remember. It's not one of the more popular or better known series - I've already checked those off the list. Any help would be greatly appreciated. I'd really like to finish the series.