I need some info on bead rollers

im helping a friend out with some tin work, he bought .040 black alu, and borrowed a bead roller from someone else (harbor freight model)
OK here's whats happening
when we make a run on a test piece the edges of the black in the alu show crack lines.
this has happened no matter what we do- change dies, put tape on the alu over the plastic, try running the bead in steps.
the first shot through you see a crack.
I think its the roller or dies them selves.
told him we should just buy a good electric one.
so I was thinking getting this one http://mittlerbros.com/bead_rollers.htm 24" and use their Nylatron dies