Mmmmm, i enchant like this:
1) Enchant weapon +4
2) Enchant another weapon till +6
3) When i reach the other weapon to +6, i enchant +4 to +5
4) Then i broke the +6 and get another weapon and i enchant to +6
5) When i reached the third weapon to +6, i enchant the first weapon from +5 to +6
6) And then like the points 3, 4, 5 ;D
The first weapon never broke ;D