Here is an easy way to cut square ends to prep brake lines for flaring. An old door hinge will pinch the line tight without collapsing or marring the surface. Lay it down on the hinge pins- that will square it 90' to the hinge leaf. You only need to pinch it lightly in your vice to be secure. Lay a fine tooth wide hacksaw blade against the leaf, cut slow and easy. A cheap V-groove router bit makes an excellent deburring tool. The end of the line in the photo has been done with this technique; nice result, ready to flare. The line used here is the copper/zinc type; not cheap, but makes a really fine line. If your cut is a wee bit off 90', you can square this line with 220 grit on a flat surface. Oh yes, don't use the router bit in a router- by hand will do just fine.