I've heard that when you chop the trunk of a tree you are not supposed to chop at an angle, but instead straight across. Why is this so? Wouldn't you want to chop at an angle to develop better movement?
Another good read is Brent's article on growing trunks for bonsai. There is a section called How To Make The Cuts. he whole article is a great read. http://evergreengardenworks.com/trunks.htm